[C]Breeds farther west in North America in other types of vegetation.Influence of Riparian WoodlandAlthough the largest single element of the Kansan avifauna that reaches distributional limits in Kansas is made up of birds of the eastern deciduous forest, several species of the eastern woodlands are present in Kansas along the east-west river drainages in riparian woodland; the species are listed inTable 8. Twenty-one kinds are involved if we include the Cooper Hawk, Yellow-billed Cuckoo, Orchard Oriole, Summer Tanager, Rufous-sided Towhee, and Chipping Sparrow, all of which breed farther to the west but are present in western Kansas only along river drainages. This leaves 15 species of eastern deciduous woodlands that occur west in Kansas alongriparian woodland (versus30 species that drop out chiefly where eastern woodland drops out). These 15 species are about one-third of all woodland birds in western Kansas. Riparian woodland does not seem to afford first-rate habitat for most of the eastern woodland species that do occur; breeding density seems to be much lower than in well-situated eastern woodland.The importance of these linear woodlands as avenues for gene-flow between eastern and western populations, especially of species-pairs (grosbeaks, flickers, orioles, and buntings), is obviously great. Likewise significant is the existence of these alleys for dispersal from the west of certain species (for instance, the Black-billed Magpie and the Scrub Jay) into new but potentially suitable areas.BREEDING SEASONSIntroductionAn examination of breeding seasons or schedules is properly undertaken at several levels. The fundamental description of variation in breeding schedules must itself be detailed in several ways and beyond this there are causal factors needing examination. The material below is a summary of the information on breeding schedules of birds in Kansas, treated descriptively and analytically in ways now thought to be of use.Almost any event in actual reproductive activity has been used in the following report; nestbuilding, egg-laying, incubation, brooding of young, feeding of young out of the nest are considered to be of equal status. To any such event days are added or subtracted from the date of observation so as to yield the date when the clutch under consideration was completed.Such corrected dates can be used in making histograms that show the time of primary breeding activity, or the "egg-season." All such schedules are generalizations; data are used for a species from any year of observation, whether 50 years ago or less than one year ago. One advantage of such procedure is that averages and modes are thus more nearly representative of the basic temporal adaptations of the species involved, as is explained below.When information on the schedule of a species from one year is lumped with information from another year or other years, two (and ordinarily more than two) frequency distributions are used to make one frequency distribution. The great advantage here is that the frequency distribution composed of two or more frequency distributions is more stable than any one of its components. Second, the peak of the season, the mode of egg-laying, is represented morebroadly than it would have been for any one year alone. Third, the extremes of breeding activity are fairly shown as of minute frequency and thus of limited importance, which would not be true if just one year were graphed. All these considerations combine to support the idea that general schedules in fact represent the basic temporal adaptations of a species much better than schedules for one year only.Variation in Breeding SeasonsIn the chronology of breeding seasons of birds, there are three basic variables: time at which seasons begin, time at which seasons end, and time in which the major breeding effort occurs. These variables have been examined in one population through time (Lack, 1947; Snow, 1955; Johnston, 1956), in several populations of many species over wide geographic ranges (Baker, 1938; Moreau, 1950; Davis, 1953), and in several populations of one species (Lack,loc. cit.; Paynter, 1954; Johnston, 1954). The analysis below is concerned with breeding of many kinds of birds of an arbitrarily defined area and with the influence of certain ecologic and zoogeographic factors on the breeding seasons for those several species.The Influence of Seasonal Status.—Here we are interested in whether a species is broadly resident or migrant in Kansas; 70 species are available for analysis.Resident SpeciesTwenty-four species, furnishing 875 records of breeding, are here considered to be resident birds in northeastern Kansas. These species are Cooper Hawk, Red-tailed Hawk, Prairie Chicken, Bobwhite, Rock Dove, Great Horned Owl, Red-bellied Woodpecker, Hairy Woodpecker, Downy Woodpecker, Horned Lark, Blue Jay, Common Crow, Black-billed Magpie, Black-capped Chickadee, Tufted Titmouse, Carolina Wren, Bewick Wren, Mockingbird, Eastern Bluebird, Loggerhead Shrike, Starling, House Sparrow, Eastern Meadowlark, and Cardinal. The distribution of completed clutches (Fig. 1) runs from mid-January to mid-September, with a modal period in the first third of May. Conspicuous breeding activity occurs from mid-April to the first third of June.Migrant SpeciesForty-six species, furnishing 2,522 records of breeding, are considered to be migrant in northeastern Kansas. These species are Great Blue Heron, Green Heron, Swainson Hawk, American Coot,Killdeer, Upland Plover, American Avocet, Least Tern, Yellow-billed Cuckoo, Black-billed Cuckoo, Burrowing Owl, Common Nighthawk, Chimney Swift, Red-headed Woodpecker, Eastern Kingbird, Western Kingbird, Scissor-tailed Flycatcher, Great Crested Flycatcher, Eastern Phoebe, Eastern Wood Pewee, Bank Swallow, Rough-winged Swallow, Barn Swallow, Purple Martin, Brown Thrasher, Catbird, House Wren, Robin, Wood Thrush, Blue-gray Gnatcatcher, Bell Vireo, Warbling Vireo, Prothonotary Warbler, Yellow Warbler, Chat, Western Meadowlark, Red-winged Blackbird, Orchard Oriole, Baltimore Oriole, Common Grackle, Black-headed Grosbeak, Indigo Bunting, Dickcissel, Lark Sparrow, and Field Sparrow. The distribution of completed clutches runs from mid-March to the first third of September, with a modal period of egg-laying in the first third of June (Fig. 1). Conspicuous breeding activity occurs from the first third of May to the last third of June.The Influence of Dominant Foraging Adaptation.—Five categories here considered reflect broad foraging adaptation: woodland species, taking invertebrate foods in the breeding season from woody vegetation or the soil within wooded habitats; grassland species, taking invertebrate foods in the breeding season from within grassland situations; limnic species, foraging within marshy or aquatic habitats; aerial species, foraging on aerial arthropods; raptors, feeding on vertebrates or large insects.RaptorsSix species, furnishing 174 records of breeding, are here considered, as follows: Cooper Hawk, Red-tailed Hawk, Swainson Hawk, Great Horned Owl, Burrowing Owl, and Loggerhead Shrike. The distribution of clutches (Fig. 1) runs from mid-January to the first third of July and is bimodal. One period of egg-laying occurs in mid-February and a second in the last third of April. Such a distribution indicates that two basically independent groups of birds are being considered. The first peak of laying reflects activities of the large raptors, and the second peak is that of the insectivorous Burrowing Owl and Loggerhead Shrike. The peak for these two birds is most nearly coincident with that for grassland species, a category to which the Burrowing Owl might well be relegated.Fig. 1. Histograms representing breeding schedules of ten categories of Kansan birds.Fig. 1.—Histograms representing breeding schedules of ten categories of Kansan birds. Heights of columns indicate percentage of total of clutches of eggs, and widths indicate ten-day intervals of time, with the 5th, 15th, and 25th of each month as medians. The occurrences of monthly means of temperature and precipitation are indicated at the bottom of the figure.Limnic SpeciesSix species, the Great Blue Heron, Green Heron, American Coot, American Avocet, Least Tern and Red-winged Blackbird, furnish264 records of breeding. The distribution of clutches (Fig. 1) runs from mid-March to the last third of July and is bimodal. This is another heterogeneous assemblage of birds; the Great Blue Heron is responsible for the first peak, in the first third of April. The other five species, however, show fair consistency and their peak of egg-laying almost coincides with peaks for aerial foragers, woodland species, and migrants, considered elsewhere in this section.Grassland SpeciesTen species, Greater Prairie Chicken, Bobwhite, Killdeer, Upland Plover, Horned Lark, Starling, Eastern Meadowlark, Western Meadowlark, Common Grackle, and Dickcissel, furnish 404 records of breeding activity. The distribution of clutches (Fig. 1) runs from the first of March to mid-September. The peak of egg-laying occurs in the first third of May. This is coincident with the peak for resident species, perhaps a reflection of the fact that half the species in the present category are residents in northeastern Kansas.Woodland SpeciesIn this category are included species characteristic of woodland edge. Thirty-four species, furnishing 1,882 records of breeding, are here treated: Yellow-billed Cuckoo, Black-billed Cuckoo, "flicker" (includes birds thought to be relatively pure red-shafted, pure yellow-shafted, as well as clear hybrids), Red-bellied Woodpecker, Red-headed Woodpecker, Hairy Woodpecker, Downy Woodpecker, Blue Jay, Black-billed Magpie, Common Crow, Black-capped Chickadee, Tufted Titmouse, Carolina Wren, Bewick Wren, House Wren, Brown Thrasher, Catbird, Mockingbird, Robin, Wood Thrush, Eastern Bluebird, Blue-gray Gnatcatcher, Bell Vireo, Warbling Vireo, Prothonotary Warbler, Yellow Warbler, Chat, Orchard Oriole, Baltimore Oriole, Cardinal, Black-headed Grosbeak, Indigo Bunting, Lark Sparrow, and Field Sparrow. The distribution of clutches runs from the first third of March to mid-September (Fig. 1). The modal period for completed clutches is the first third of June. Conspicuous breeding activity occurs from the first third of May to mid-June. The distribution of the season in time is almost identical with that for migrant species, reflecting the large number of migrant species in woodland habitats in Kansas.Aerial ForagersTwelve species, Common Nighthawk, Chimney Swift, Eastern Kingbird, Western Kingbird, Scissor-tailed Flycatcher, Great Crested Flycatcher, Eastern Phoebe, Eastern Wood Pewee, BankSwallow, Rough-winged Swallow, Barn Swallow, and Purple Martin, furnish 587 records of breeding. The distribution of clutches (Fig. 1) extends from the last third of March to the first third of August, and the modal date of clutches is in the first third of June. Conspicuous breeding activity occurs from the end of May to the end of June. The peak of nesting essentially coincides with that characteristic of migrants.Zoogeographic CategoriesThree categories of Mayr (1946) are of use in analyzing trends in breeding schedules of birds in Kansas. These categories of presumed ultimate evolutionary origin are the "Old World Element," the "North American Element," and the "South American Element." Not always have I agreed with Mayr's assignments of species to these categories, and such differences are noted. There is some obvious overlap between these categories and those discussed previously.Old World ElementEighteen species, Red-tailed Hawk, Rock Dove, Great Horned Owl, Hairy Woodpecker, Downy Woodpecker, Black-billed Magpie, Common Crow, Black-capped Chickadee, Tufted Titmouse, Robin, Loggerhead Shrike, Starling, House Sparrow, Bank Swallow, Barn Swallow, and Blue-gray Gnatcatcher, furnish 969 records of breeding (Fig. 1). Species for which I have records but which are not here listed are the Blue Jay and the Wood Thrush, both of which I consider to be better placed with the North American Element. The distribution of completed clutches runs from mid-January to the first third of August, and shows a tendency toward bimodality. The second, smaller peak is due to the inclusion of relatively large samples of three migrant species (Robin, Bank Swallow, and Barn Swallow). The timing of the breeding seasons of these three species is in every respect like that of most other migrants; if they are removed from the present sample the bimodality disappears, indicating an increase in homogeneity of the unit.North American ElementTwenty-six species, Greater Prairie Chicken, Bobwhite, "flicker," Rough-winged Swallow, Purple Martin, Blue Jay, Carolina Wren, Bewick Wren, House Wren, Mockingbird, Catbird, Brown Thrasher, Wood Thrush, Bell Vireo, Warbling Vireo, Prothonotary Warbler, Yellow Warbler, Chat, Eastern Meadowlark, Western Meadowlark, Red-winged Blackbird, Orchard Oriole, Baltimore Oriole, CommonGrackle, Lark Sparrow, and Field Sparrow, furnish 1,233 records of breeding (Fig. 1). The distribution of completed clutches runs from the first third of April to the first third of September. The modal date for completion of clutches is June 1.South American ElementTwelve species, Eastern Kingbird, Western Kingbird, Scissor-tailed Flycatcher, Great Crested Flycatcher, Yellow-bellied Flycatcher, Traill Flycatcher, Eastern Wood Pewee, Eastern Phoebe, Cardinal, Black-headed Grosbeak, Rose-breasted Grosbeak, and Indigo Bunting, furnish 552 records of breeding (Fig. 1). The curve representing this summary schedule is bimodal, wholly as a result of including the Eastern Phoebe and the Cardinal with this sample.Relationship of Schedules to Temperature and PrecipitationIn outlining the ten categories above, attention has been given to certain similarities and differences in the frequency distributions. A slightly more refined way of comparing the frequency distributions is to relate them to other, seasonally variable phenomena. Figure 1 shows the frequency distributions of egg-laying of these ten categories of birds in terms of the regular changes in mean temperature and mean precipitation characteristic of the environments in which these birds live in the breeding season.Table 9shows that there are two basic groups of birds according to peak of egg-laying and incidence of precipitation; raptors, birds of Eurasian origin, resident birds, and birds of grassland habitats tend to have their peaks of egg-laying prior to the peak of spring-summer rains, and the other six categories tend to have their peaks of egg-laying occur in the time of spring-summer rains. Regarding temperature, there are four categories of birds; these are evident in the table.Some of the correspondences deserve comment. Residents and grassland species both breed before the rains come and before mean temperatures reach 70°F., and this correspondence probably results from most of the grassland species being residents. Contrariwise, most birds of Eurasian stocks are residents, but not all residents are of such stocks; the two groups are discrete when mean temperature at breeding is considered. Woodland birds, aerial foragers, and birds of South American evolutionary stocks breed after temperatures surpass 70°F. on the average. Almost all such species are migrants, but many migrants have different temporal characteristics, and the categories thus are shown to be discrete on the basis of temperature at time of breeding.The change through spring and summer of temperature and precipitation delineates the inception and waxing of the growing season of vegetation and of the subsequent arthropod populations, on which most of the birds feed in the breeding season. The temporal characteristics of growing seasons in North America have been treated by Hopkins (1938) and have been related to timing of breeding seasons in Song Sparrows (Passerella melodia) of the Pacific coast of North America (Johnston, 1954).Significance of Phylogeny to Breeding SchedulesEvidence from a variety of sources demonstrates that timing of breeding seasons is either broadly or specifically genetically-determined. For some species in some situations major environmental variables are paramount in regulating timing of breeding, but in others the innate, regulatory "clock" is less closely tied to conspicuous exogenous stimuli. The work by Miller (1955a, 1955b, 1960) with several species ofZonotrichiastrongly indicates that endogenous timing is most important for these birds, and there is ecological evidence for Song Sparrows that supports the same point (Johnston, 1954, 1956). It is, in any event, possible to treat breeding schedules as species-specific characters, for any one geographic area.In an attempt to relate a breeding schedule to previous ancestral modes, that is by extension to phylogeny, it is necessary to know how often ancestral adaptations can persist in the face of necessity to adapt to present environmental conditions. It is necessary to know how conservative or how immediately plastic breeding schedules can be. The disadvantage of using available information about configurations of breeding seasons (as shown in Figs. 3 to 9) is that it is extremely difficult to compare visually at one time more than six or eight histograms as to the trenchant similarities and differences regarding times of inception and cessation of breeding, and time of peak egg-laying. It is possible, however, to reduce these three variables to one variable (as described below), which allows the necessary comparisons to be made more easily; this variable may be called thebreeding index.Calculation of Breeding IndexThe chronological year is broken roughly into ten-day intervals numbered 1 to 36. The histogram describing the temporal occurrence of the breeding season of a species in our area usually will lie within intervals 7 to 25. The modal date for completion of clutches is given a value corresponding to the number of ten-dayintervals beyond interval 7 (March 1-10); this describes the modal variable. The date of completion of 83 per cent of all clutches is given a value corresponding to the number of ten-day intervals it lies from interval 11 (April 11-20); this describes the 83 per cent variable (and is a measure of the length of the season in terms of its inception). The breeding index can then be calculated as follows:I =Xm+Xsd,where:I is the breeding index,Xmis the modal variable, andXsdis the 83 per cent variable.This is obviously an arbitrary scheme to gain a simple measure of beginning, peak, and end of a breeding season. Other schemes could be devised whereby different absolute values would be involved, but the relative nature of the results would be preserved. The values under the present system for 73 species of Kansan birds run from -5 to +22; early modal dates and cessation to breeding give low values, late dates high values.Within this framework there are other, presumably subordinate, factors that influence the values of breeding indices, as follows:1. Migratory habit. Any migrant tends to arrive on breeding grounds relatively late, hence migrants ordinarily have higher index values than do residents.2. Colonial breeding. The strong synchrony of colonially-breeding species tends to move the modal egg-date toward the time of inception of breeding; as a result colonially-breeding species probably have lower index values than they would have if not colonial.3. Single-broodedness. Species having only one brood per season tend to have shorter seasons than double-brooded species, and their index values tend to be lower than those of double-brooded species.Migratory habit unquestionably has considerable influence on index values in some species. It is not, however, as important as other matters, such as the condition of the food substratum or sensitivity of the pituitary-gonadal mechanism, in determining timing and mode of breeding activity. The schedule of the Purple Martin is the extreme example showing that time of spring arrival on breeding grounds is not necessarily related to time of inception of breeding. It should be emphasized that the factors leading to northward migratory movement may be involved in timing of the annual gonadal and reproductive cycle.Figure 2 presents a graphic summary of values of breedingindices for many groups of Kansan birds. The values for species of a given family have been linked by a horizontal line. The length of this line is proportional to the degree to which the index values for the species concerned resemble one another. Note that the plottings for the Picidae, Corvidae, Turdidae, Tyrannidae, and Icteridae each contain one point that is well-removed from a cluster of points. This can be interpreted as a measure of the frequency of adaptive plasticity versus adaptive conservatism; five of the 24 plottings show a plastic character, 19 a conservative. There are 26 plottings that show temporal consistency, all of which may be taken as evidence of adaptive (or relictual) conservatism of the species in question.Fig. 2.—Breeding indices for Kansan birds.Fig.2.—Breeding indices for Kansan birds. Vertical hash-marks indicate the value of breeding index for a given species; horizontal lines show the range of values of breeding index for families and orders.ConclusionSuch patterns of breeding chronology support the idea that seasonal response to the necessities of breeding is conservative more often than plastic. Most students of breeding schedules believe that since these are highly adaptive, they must also be capable of flexibility to meet variable environments within the range of the species. Such thinking receives support when different geographic localities are considered for one species (Johnston, 1954), or when specific features of a special environment are considered (see Miller, 1960; Johnston, 1956).Yet, if one, relatively restricted locality is considered, as in the present study, evidence of a conservative characteristic in breeding schedules can be detected. This conservatism may result from the historic genetic "burden" of the species; that is to say, previous adaptive peaks may in part be evident in the matrix of contemporary adaptation. Adaptive relicts of morphological nature have been many times documented, but characteristics associated with seasonality and timing schedules have not.In any event, genetic relationships are evident in the configuration of breeding seasons of many species here treated. Thus, any consideration of variation in breeding schedules must be sensitive to the limits, whether broad or restricting, that the heritage of a species sets on its present chronological adaptation.Regulation of Breeding SchedulesRegulation of breeding schedules in birds always involves some exogenous, environmental timing or triggering mechanism. Broad limits to functional reproductive activity seem to be set by the photoperiod—neuroendocrine system. This basic, predominately extra-equatorial, regulator can be ignored by temperate-zone species only if they possess chronological adaptation to special, aperiodic environmental conditions, as does the Red Crossbill (Loxia curvirostra; see McCabe and McCabe, 1933; H. B. Tordoff, ms.), for which the chief consideration seems to be availability of conifer seeds. Environmental phonomena otherwise known to trigger breeding activity include rainfall (Davis, 1953; Williamson, 1956), presence of suitable nesting material (Marshall and Disney, 1957; Lehrman, 1958), temperature (Nice, 1937), and presence of a mate (Lehrman, Brody, and Wortis, 1961). Such regulators, or environmental oscillators, are the "phasing factors" of the physiologic clock that dictate the temporal occurrence of primary reproductive activity.None of the regulators mentioned above has been specifically investigated for any Kansan bird, but it is reasonable to suppose that, in these temperate-zone species, the photoperiod is the most important general phasing factor in seasonal breeding. Although gonadal response and seasonal restriction of breeding are set by the photoperiod, specific temporal relationships are dictated by more immediate environmental variables.Table 9.—Relationship Between Environmental Factors and Timing of Breeding in Birds of KansasOccurrence of Peak of Egg-layingWhen Precipitation is:When Mean Temperature (F.) is:LightHeavy< 55°< 70°± 70°> 70°RaptorsxxO. W. ElementxxResidentsxxGrassland speciesxxMarshland speciesxxN. Amer. ElementxxMigrantsxxWoodland speciesxxAerial foragersxxS. Amer. ElementxxTable 9, as already noted, shows the gross relationships between certain groups of birds, certain arbitrary indicators of seasonal temperature-humidity conditions bearing significantly on the growing season, and occurrence in time of peak of egg-laying by the birds involved. Some species and groups of Kansan birds breed chiefly under cool-dry environmental conditions, and some under warm-wet environmental conditions. Within each of these categories some variation occurs. Thus, raptors and boreally-adapted species (the Eurasian zoogeographic element) breed under cool conditions prior to rains, and residents and grassland species breed under slightly warmer conditions prior to rains; limnic species, species derived from North American evolutionary stocks, and migrants tend to breed in the cooler segment of the warm-wet period, and woodland birds, aerial foragers, and species derived from South American evolutionary stocks tend to breed in the warmer segment of the warm-wet period.So much, then, for relationships between birds and their environmentsat a descriptive level. It would be useful at this point to examine how environmental variables relate to timing of breeding. Certain independent lines of investigation indicate that birds have a well-developed internal timing device; most convincing is the work of Schmidt-Koenig (1960) and the others who have shown that the endogenous clock of birds can be shifted in its periodicity forward or backward in time. This and much other evidence (see Brown, 1960) indicate that many fundamental periodic regulators are extrinsic to the animal; it is thus permissible for present purposes to consider any expression of variation in timing as dependent on environmental oscillators. It is not hereby meant to ignore the fact that differential responses to dominant environmental variables occur within a species, indicating endogenous control over timing of breeding. The work by Miller (1960:518) with three populations of the White-crowned Sparrow, revealing innately different responses to vernal photoperiodic increase, is especially important in this regard. For the moment, however, we may consider exogenous controls only.Any exogenous control, or environmental variable, can be looked on simply as a timing oscillator. Such variables show regular or irregular periodic activity, and the independent actions as a whole result in the more-or-less variable annual schedule of breeding for any species at any one place. It would seem that some oscillators are linked to one another, but there is a real question concerning the over-all degree to which linkage is present. It is significant that frequency distributions of breeding activity of various species and groups of birds take on the shape of a skewed normal curve. The more information is added to such distributions, the more nearly they approach being wholly normal, with irregularities tending to disappear. This kind of response itself is evidence that most of the variables influencing the distribution are not mutually linked.This conclusion is warranted if we examine what would happen to frequency distributions if the variables or oscillators regulating timing were linked. The frequency distribution of breeding activity in birds is described by a nonlinear curve (a normal distribution is nonlinear). Let us assume that each of the environmental variables is a nonlinear oscillator, as is probable. A set of nonlinear oscillators mutually entrained or coupled and operating with reference to a given phenomenon would result in that phenomenon being described by a frequency distribution much more stable than if it were regulated by any one oscillator alone. However, the frequency distribution of a setof coupled nonlinear oscillators is non-normal (Wiener, 1958).We do not obtain such distributions in describing breeding activity, so we may say that the oscillators regulating such activity are not coupled. Present distribution, habitat preference, residency status, foraging adaptation, previous zoogeographic history, and relicts of ancestral adaptation, all bear on the character of the breeding schedule of any bird species. The emphasis above on multiple regulation of breeding schedules conceivably reflects the true picture, but any such emphasis is made at the expense of taking one factor as basic, or reducing the many to one, in order to manufacture simplicity.ACCOUNTS OF SPECIESIn each account below information is given concerning status, habitat, geographic distribution, seasonal occurrence, schedule of egg-laying, number of eggs laid, and sites of nests, as these pertain to Kansas, unless otherwise stated. The ways in which some of these points were elucidated are as follows.1.—Breeding schedule. Frequency distributions of egg-laying in time are calculated on the basis of dates of completed clutches, as described earlier (p. 588). Any event in the series of actions of nesting—nestbuilding, egg-laying, incubation, brooding, feeding young out of nests—can be manipulated by adding or subtracting days to or from the date of record to yield the probable date of completion of the clutch. The resulting data are grouped into class intervals of ten days. Extreme dates here given for egg-laying may be as much as nine days off in accuracy, but the error does not often exceed five days. Extreme dates indicated here may be taken as actual or predicted extremes. The raw data used are on file at the Museum of Natural History and are available for use by any qualified individual.2.—Dates of occurrence. First and last annual occurrences in the State for migrant species are indicated by both a range of dates and a median date. Twenty to 30 dates of first observation in spring are available for most of the common species, and 10 to 20 dates of last observation in autumn are at hand for such species. The median dates, earlier than and subsequent to which an equal number of observations are available, are reliable indicators of the dates on which a species is likely to be seen first in the State in an average year.3.—Clutch-size. Information on number of eggs is given for each species according to the mode, followed by the mean, the range, and the size of the sample.4.—Distribution in Kansas. Information on distribution in the breeding season within the borders of Kansas is given in accounts below chiefly by reference to one or more counties of the State. Location of counties can be made by referring to Figure 10.Pied-billed Grebe:Podilymbus podiceps podiceps(Linnaeus).—This is a common but local summer resident, in and on ponds, marshes, streams, ditches, and lakes. The species can be seen in the State at any time, but usually arrives in the period March 1 to April 13 (the median is March 21), and departs southward in the period October 13 to November 18 (the median is October 24).Breeding schedule.—Nineteen records of breeding span the period May 1 to June 30; the modal date for egg-laying is May 15.Number of eggs.—Clutch-size is 4 to 10 eggs.Nests are floating masses of marsh vegetation (cattail, smartweed, duckweed, filamentous green algae, and the like), kept green on top by addition of fresh material, in or at the edge of emergent marsh vegetation.Double-crested Cormorant:Phalacrocorax auritus auritus(Lesson).—This is a transient, but has been found nesting on one occasion in Barton County (Tordoff, 1956:311).Breeding schedule.—Eggs were laid in July and August in the one known nesting effort.Number of eggs.—Clutch-size is 2 to 4 eggs (Davie, 1898).Great Blue Heron:Ardea herodiasLinnaeus.—This common summer resident nests in tall trees along rivers, streams, and marshes. The sector of greatest abundance is the Flint Hills.A. h. herodiasLinnaeus occurs in extreme northeastern Kansas,A. h. wardiRidgway breeds in southeastern Kansas, andA. h. treganzaiCourt breeds in western Kansas; specimens showing intermediate morphology have been taken from the central part of the State. Occurrence in time, exclusive of the few that overwinter in Kansas, is shown inTable 10.Breeding schedule.—Seventy-seven records of breeding span the period March 1 to April 30 (Fig. 3); the modal date of egg-laying is April 5.Number of eggs.—Clutch-size is 4 eggs (4.4, 3-6; 36).Nests are placed in crotches of sycamore, cottonwood, elm, hackberry, oak, and walnut, from 30 to 60 feet high; the average height is about 40 feet.Table 10.—Occurrence in Time of Summer Resident Herons in KansasSpeciesArrivalDepartureRangeMedianRangeMedianGreat Blue HeronFeb. 4-Apr. 8Mar. 20Oct. 10-Nov. 29Oct. 23Green HeronMar. 29-May 4Apr. 27Sept. 1-Oct. 30Sept. 9Common EgretApr. 8-May 12Apr. 2Sept. 4-Sept. 30Sept. 21Black-crowned Night HeronMar. 27-May 18Apr. 25Sept. 10-Nov. 11Sept. 25Yellow-crowned Night HeronApr. 15-May 18Apr. 27................American BitternApr. 4-May 9May 1Oct. 6-Dec. 12Oct. 16Least BitternApr. 9-May 22Apr. 8Oct. 24........Green Heron:Butorides virescens virescens(Linnaeus).—This is a common summer resident about streams, lakes, and marshes throughout the State. Some characteristics of the temporal occurrence of this species are indicated inTable 10.Breeding schedule.—Twenty-eight records of breeding span the period April 21 to June 20 (Fig. 3); the modal date of completion of clutches is May 5.Number of eggs.—Clutch-size is 3 eggs (3.1, 3-5; 17).Nests are placed about 10 feet high (two to 35 feet) in willow, cottonwood, elm, and the like.Little Blue Heron:Florida caerulea caerulea(Linnaeus).—This is chiefly a postbreeding summer visitant, but there is one record of breeding in Finney County (Tordoff, 1956:312).Breeding schedule.—There is no information on breeding schedule in Kansas or in adjacent areas.Number of eggs.—Clutch-size is 2 to 4 eggs (Davie, 1898).Nests are placed in trees and bushes at various heights above the ground.Common Egret:Casmerodius albus egretta(Gmelin).—This is a postbreeding summer visitant, but has been found nesting once in Cowley County (Johnston, 1960:10). Occurrence in time is listed inTable 10.Breeding schedule.—There is no information on breeding schedule in Kansas.Number of eggs.—Clutch-size is 2 to 4 eggs (Davie, 1898).Nests are placed in trees, usually above 20 feet in height; the one instance of nesting in the State was within a colony of Great Blue Herons.Snowy Egret:Leucophoyx thula thula(Molina).—This postbreeding summer visitant has been found nesting once in Finney County (Tordoff, 1956:312).Breeding schedule.—There is no information on breeding schedule in the State.Number of eggs.—Clutch-size is 2 to 5 eggs (Davie, 1898).Nests in Kansas are placed among those of Great Blue Herons.Black-crowned Night Heron:Nycticorax nycticorax hoactli(Gmelin).—This is a locally common summer resident around marshes and riparian habitats. Characteristics of the occurrence of the species in time are given inTable 10.Breeding schedule.—Eggs are laid in the period May 1 to August 10.Number of eggs.—Clutch-size is about 4 eggs.Nests are placed at medium elevations in riparian trees, in Kansas chiefly cottonwood, or in beds of emergent marsh vegetation.Yellow-crowned Night Heron:Nyctanassa violacea violacea(Linnaeus).—This is a local summer resident in riparian habitats, chiefly in southeastern Kansas. Specimens taken in the breeding season and records of nesting come from Meade, Stafford, Doniphan, Douglas, Greenwood, Woodson, Labette, and Cherokee counties. Characteristics ofoccurrence in time in Kansas are shown inTable 10.Breeding schedule.—Eggs are laid in May and June.Number of eggs.—Clutch-size is about 4 eggs.Nests are placed in riparian trees.Least Bittern:Ixobrychus exilis exilis(Gmelin).—This is a local summer resident in marshland. Characteristics of its occurrence in time are indicated inTable 10.Breeding schedule.—Eleven records of breeding span the period May 21 to July 20; the modal date of egg-laying seems to be in the first week of June.Number of eggs.—Clutch-size is about 4 eggs.Nests are placed in dense emergent vegetation a few inches to a foot above the surface of the water.American Bittern:Botaurus lentiginosus(Rackett).—This is a local summer resident in marshes and heavy grassland. The species occurs temporally according to characteristics as listed inTable 10.Breeding schedule.—Eggs are laid in May and probably in June.Number of eggs.—Clutch-size is 3 or 4 eggs.Nests are placed on the ground in heavy cover.White-faced Ibis:Plegadis chihi(Vieillot).—This is a local summer resident in marshland; actual records of breeding come only from Barton County (Nossaman, 1952:7; Zuvanich, 1963; M. Schwilling, personal communication, July, 1962). The species has been recorded in the State from April 17 to October 6.Breeding schedule.—Twenty-five breeding records are for June and early July.Number of eggs.—Clutch-size is about 4 eggs (3.9, 3-4; 24).Nests are placed in emergent marsh vegetation near the surface of the water, in Barton County in extensive cattail beds harboring also Black-crowned Night Herons.Mallard:Anas platyrhynchos platyrhynchosLinnaeus.—This is a local summer resident around marshes. The time of greatest abundance is October to April, but most birds move north for breeding.Breeding schedule.—Fifteen records of breeding span the period April 1 to June 10; the modal date of egg-laying is in the first ten days of May.Number of eggs.—Clutch-size varies widely; first clutches are of about 12 eggs. Brood sizes vary from 3 to 12 individuals in Kansas.Nests are placed on the ground surface, in pasture grasses, marsh grasses, cattail, sedge, and smartweed.Pintail:Anas acutaLinnaeus.—This is a local summer resident in marshland. The time of greatest abundance is from September to May, but most birds move north for breeding.Breeding schedule.—Eleven records of breeding span the period April 21 to June 10; the peak of egg-laying seems to be in the period May 1 to 10.Number of eggs.—Clutch-size is around 10 eggs. Brood sizes vary from 3 to 8 individuals in Kansas.Nests are placed on the ground surface, in cover of marsh grass,cattail, or sedge.Blue-winged Teal:Anas discors discorsLinnaeus.—This summer resident is locally common around marshes and ponds. The species arrives in spring in the period March 9 to April 5 (the median is March 23); birds are last seen sometime between October 7 and November 26 (the median is October 20).Breeding schedule.—Twenty-two records of breeding span the period May 1 to May 30; the peak of egg-laying is around May 15. It is doubtful that the present data indicate the full extent of the egg-season in this duck.Number of eggs.—Clutch-size is 8 to 12 eggs.Nests are placed on the ground surface, in cover of grasses, cattail and sedges.Shoveler:Anas clypeataLinnaeus.—This is an irregular and local summer resident, around marshes. Most individuals seen in the State are passage migrants. Breeding records are from Barton and Finney counties.Breeding schedule.—Seasonal limits are unknown for the Shoveler in Kansas.Number of eggs.—Clutch-size is about 8 eggs (Davie, 1898).Nests are placed on the ground surface in cover of marsh vegetation.Wood Duck:Aix sponsa(Linnaeus).—This is an uncommon summer resident around wooded streams and ponds in eastern Kansas. Nesting records and specimens taken in the breeding season come from east of stations in Pottawatomie, Coffey, and Woodson counties. Most nesting records at present come from the Marais des Cygnes Wildlife Refuge, Linn County. The species is present in the State from March 5 to December 8.Breeding schedule.—Eleven records of breeding span the period March 21 to May 10; the peak of egg-laying is probably in mid-April. The present data are inadequate for showing the full span of the breeding season.Number of eggs.—Clutch-size is around 15 eggs, varying from 10 to 23 in the sample at hand.Nests are placed in crevices and hollows in trees near water, 10 to 70 feet high.Redhead:Aythya americana(Eyton).—This duck nested at Cheyenne Bottoms, Barton County, 1962: 9 eggs found May 31 (M. Schwilling); also reported to have nested at Cheyenne Bottoms about 1928 (Tordoff, 1956:316).Canvasback:Aythya valisineria(Wilson).—This duck nested at Cheyenne Bottoms, Barton County, 1962: 14 eggs found June 20 (M. Schwilling).Ruddy Duck:Oxyura jamaicensis rubida(Wilson).—This is a local summer resident in marshland; numbers seem generally higher in western than in eastern Kansas. The season of greatest abundance is March through November, but numbers are conspicuously reduced in midsummer.Breeding schedule.—Eggs are known to be laid in May and June.Number of eggs.—Clutch-size is about 10 eggs (Davie, 1898).Nests are placed near the edge of water, either in or on emergent marsh vegetation; nests of other marshland birds, such as coots, are sometimes appropriated (Davie, 1898).Turkey Vulture:Cathartes aura teterFriedmann.—This summer resident is common throughout Kansas. Occurrence in time is indicated inTable 11.Breeding schedule.—Fifteen records of breeding span the periodApril 21 to June 10; earlier records will doubtless be found, to judge from the frequency distribution of the present sample. The peak of egg-laying is perhaps around May 1.Number of eggs.—Clutch-size is 2 eggs (1.8, 1-2; 12).Nests are placed in holes and crevices in trees and cliffs, on rocky ledges, and the like.
[C]Breeds farther west in North America in other types of vegetation.
Influence of Riparian Woodland
Although the largest single element of the Kansan avifauna that reaches distributional limits in Kansas is made up of birds of the eastern deciduous forest, several species of the eastern woodlands are present in Kansas along the east-west river drainages in riparian woodland; the species are listed inTable 8. Twenty-one kinds are involved if we include the Cooper Hawk, Yellow-billed Cuckoo, Orchard Oriole, Summer Tanager, Rufous-sided Towhee, and Chipping Sparrow, all of which breed farther to the west but are present in western Kansas only along river drainages. This leaves 15 species of eastern deciduous woodlands that occur west in Kansas alongriparian woodland (versus30 species that drop out chiefly where eastern woodland drops out). These 15 species are about one-third of all woodland birds in western Kansas. Riparian woodland does not seem to afford first-rate habitat for most of the eastern woodland species that do occur; breeding density seems to be much lower than in well-situated eastern woodland.
The importance of these linear woodlands as avenues for gene-flow between eastern and western populations, especially of species-pairs (grosbeaks, flickers, orioles, and buntings), is obviously great. Likewise significant is the existence of these alleys for dispersal from the west of certain species (for instance, the Black-billed Magpie and the Scrub Jay) into new but potentially suitable areas.
BREEDING SEASONS
Introduction
An examination of breeding seasons or schedules is properly undertaken at several levels. The fundamental description of variation in breeding schedules must itself be detailed in several ways and beyond this there are causal factors needing examination. The material below is a summary of the information on breeding schedules of birds in Kansas, treated descriptively and analytically in ways now thought to be of use.
Almost any event in actual reproductive activity has been used in the following report; nestbuilding, egg-laying, incubation, brooding of young, feeding of young out of the nest are considered to be of equal status. To any such event days are added or subtracted from the date of observation so as to yield the date when the clutch under consideration was completed.
Such corrected dates can be used in making histograms that show the time of primary breeding activity, or the "egg-season." All such schedules are generalizations; data are used for a species from any year of observation, whether 50 years ago or less than one year ago. One advantage of such procedure is that averages and modes are thus more nearly representative of the basic temporal adaptations of the species involved, as is explained below.
When information on the schedule of a species from one year is lumped with information from another year or other years, two (and ordinarily more than two) frequency distributions are used to make one frequency distribution. The great advantage here is that the frequency distribution composed of two or more frequency distributions is more stable than any one of its components. Second, the peak of the season, the mode of egg-laying, is represented morebroadly than it would have been for any one year alone. Third, the extremes of breeding activity are fairly shown as of minute frequency and thus of limited importance, which would not be true if just one year were graphed. All these considerations combine to support the idea that general schedules in fact represent the basic temporal adaptations of a species much better than schedules for one year only.
Variation in Breeding Seasons
In the chronology of breeding seasons of birds, there are three basic variables: time at which seasons begin, time at which seasons end, and time in which the major breeding effort occurs. These variables have been examined in one population through time (Lack, 1947; Snow, 1955; Johnston, 1956), in several populations of many species over wide geographic ranges (Baker, 1938; Moreau, 1950; Davis, 1953), and in several populations of one species (Lack,loc. cit.; Paynter, 1954; Johnston, 1954). The analysis below is concerned with breeding of many kinds of birds of an arbitrarily defined area and with the influence of certain ecologic and zoogeographic factors on the breeding seasons for those several species.
The Influence of Seasonal Status.—Here we are interested in whether a species is broadly resident or migrant in Kansas; 70 species are available for analysis.
Resident Species
Twenty-four species, furnishing 875 records of breeding, are here considered to be resident birds in northeastern Kansas. These species are Cooper Hawk, Red-tailed Hawk, Prairie Chicken, Bobwhite, Rock Dove, Great Horned Owl, Red-bellied Woodpecker, Hairy Woodpecker, Downy Woodpecker, Horned Lark, Blue Jay, Common Crow, Black-billed Magpie, Black-capped Chickadee, Tufted Titmouse, Carolina Wren, Bewick Wren, Mockingbird, Eastern Bluebird, Loggerhead Shrike, Starling, House Sparrow, Eastern Meadowlark, and Cardinal. The distribution of completed clutches (Fig. 1) runs from mid-January to mid-September, with a modal period in the first third of May. Conspicuous breeding activity occurs from mid-April to the first third of June.
Migrant Species
Forty-six species, furnishing 2,522 records of breeding, are considered to be migrant in northeastern Kansas. These species are Great Blue Heron, Green Heron, Swainson Hawk, American Coot,Killdeer, Upland Plover, American Avocet, Least Tern, Yellow-billed Cuckoo, Black-billed Cuckoo, Burrowing Owl, Common Nighthawk, Chimney Swift, Red-headed Woodpecker, Eastern Kingbird, Western Kingbird, Scissor-tailed Flycatcher, Great Crested Flycatcher, Eastern Phoebe, Eastern Wood Pewee, Bank Swallow, Rough-winged Swallow, Barn Swallow, Purple Martin, Brown Thrasher, Catbird, House Wren, Robin, Wood Thrush, Blue-gray Gnatcatcher, Bell Vireo, Warbling Vireo, Prothonotary Warbler, Yellow Warbler, Chat, Western Meadowlark, Red-winged Blackbird, Orchard Oriole, Baltimore Oriole, Common Grackle, Black-headed Grosbeak, Indigo Bunting, Dickcissel, Lark Sparrow, and Field Sparrow. The distribution of completed clutches runs from mid-March to the first third of September, with a modal period of egg-laying in the first third of June (Fig. 1). Conspicuous breeding activity occurs from the first third of May to the last third of June.
The Influence of Dominant Foraging Adaptation.—Five categories here considered reflect broad foraging adaptation: woodland species, taking invertebrate foods in the breeding season from woody vegetation or the soil within wooded habitats; grassland species, taking invertebrate foods in the breeding season from within grassland situations; limnic species, foraging within marshy or aquatic habitats; aerial species, foraging on aerial arthropods; raptors, feeding on vertebrates or large insects.
Raptors
Six species, furnishing 174 records of breeding, are here considered, as follows: Cooper Hawk, Red-tailed Hawk, Swainson Hawk, Great Horned Owl, Burrowing Owl, and Loggerhead Shrike. The distribution of clutches (Fig. 1) runs from mid-January to the first third of July and is bimodal. One period of egg-laying occurs in mid-February and a second in the last third of April. Such a distribution indicates that two basically independent groups of birds are being considered. The first peak of laying reflects activities of the large raptors, and the second peak is that of the insectivorous Burrowing Owl and Loggerhead Shrike. The peak for these two birds is most nearly coincident with that for grassland species, a category to which the Burrowing Owl might well be relegated.
Fig. 1. Histograms representing breeding schedules of ten categories of Kansan birds.Fig. 1.—Histograms representing breeding schedules of ten categories of Kansan birds. Heights of columns indicate percentage of total of clutches of eggs, and widths indicate ten-day intervals of time, with the 5th, 15th, and 25th of each month as medians. The occurrences of monthly means of temperature and precipitation are indicated at the bottom of the figure.
Limnic Species
Six species, the Great Blue Heron, Green Heron, American Coot, American Avocet, Least Tern and Red-winged Blackbird, furnish264 records of breeding. The distribution of clutches (Fig. 1) runs from mid-March to the last third of July and is bimodal. This is another heterogeneous assemblage of birds; the Great Blue Heron is responsible for the first peak, in the first third of April. The other five species, however, show fair consistency and their peak of egg-laying almost coincides with peaks for aerial foragers, woodland species, and migrants, considered elsewhere in this section.
Grassland Species
Ten species, Greater Prairie Chicken, Bobwhite, Killdeer, Upland Plover, Horned Lark, Starling, Eastern Meadowlark, Western Meadowlark, Common Grackle, and Dickcissel, furnish 404 records of breeding activity. The distribution of clutches (Fig. 1) runs from the first of March to mid-September. The peak of egg-laying occurs in the first third of May. This is coincident with the peak for resident species, perhaps a reflection of the fact that half the species in the present category are residents in northeastern Kansas.
Woodland Species
In this category are included species characteristic of woodland edge. Thirty-four species, furnishing 1,882 records of breeding, are here treated: Yellow-billed Cuckoo, Black-billed Cuckoo, "flicker" (includes birds thought to be relatively pure red-shafted, pure yellow-shafted, as well as clear hybrids), Red-bellied Woodpecker, Red-headed Woodpecker, Hairy Woodpecker, Downy Woodpecker, Blue Jay, Black-billed Magpie, Common Crow, Black-capped Chickadee, Tufted Titmouse, Carolina Wren, Bewick Wren, House Wren, Brown Thrasher, Catbird, Mockingbird, Robin, Wood Thrush, Eastern Bluebird, Blue-gray Gnatcatcher, Bell Vireo, Warbling Vireo, Prothonotary Warbler, Yellow Warbler, Chat, Orchard Oriole, Baltimore Oriole, Cardinal, Black-headed Grosbeak, Indigo Bunting, Lark Sparrow, and Field Sparrow. The distribution of clutches runs from the first third of March to mid-September (Fig. 1). The modal period for completed clutches is the first third of June. Conspicuous breeding activity occurs from the first third of May to mid-June. The distribution of the season in time is almost identical with that for migrant species, reflecting the large number of migrant species in woodland habitats in Kansas.
Aerial Foragers
Twelve species, Common Nighthawk, Chimney Swift, Eastern Kingbird, Western Kingbird, Scissor-tailed Flycatcher, Great Crested Flycatcher, Eastern Phoebe, Eastern Wood Pewee, BankSwallow, Rough-winged Swallow, Barn Swallow, and Purple Martin, furnish 587 records of breeding. The distribution of clutches (Fig. 1) extends from the last third of March to the first third of August, and the modal date of clutches is in the first third of June. Conspicuous breeding activity occurs from the end of May to the end of June. The peak of nesting essentially coincides with that characteristic of migrants.
Zoogeographic Categories
Three categories of Mayr (1946) are of use in analyzing trends in breeding schedules of birds in Kansas. These categories of presumed ultimate evolutionary origin are the "Old World Element," the "North American Element," and the "South American Element." Not always have I agreed with Mayr's assignments of species to these categories, and such differences are noted. There is some obvious overlap between these categories and those discussed previously.
Old World Element
Eighteen species, Red-tailed Hawk, Rock Dove, Great Horned Owl, Hairy Woodpecker, Downy Woodpecker, Black-billed Magpie, Common Crow, Black-capped Chickadee, Tufted Titmouse, Robin, Loggerhead Shrike, Starling, House Sparrow, Bank Swallow, Barn Swallow, and Blue-gray Gnatcatcher, furnish 969 records of breeding (Fig. 1). Species for which I have records but which are not here listed are the Blue Jay and the Wood Thrush, both of which I consider to be better placed with the North American Element. The distribution of completed clutches runs from mid-January to the first third of August, and shows a tendency toward bimodality. The second, smaller peak is due to the inclusion of relatively large samples of three migrant species (Robin, Bank Swallow, and Barn Swallow). The timing of the breeding seasons of these three species is in every respect like that of most other migrants; if they are removed from the present sample the bimodality disappears, indicating an increase in homogeneity of the unit.
North American Element
Twenty-six species, Greater Prairie Chicken, Bobwhite, "flicker," Rough-winged Swallow, Purple Martin, Blue Jay, Carolina Wren, Bewick Wren, House Wren, Mockingbird, Catbird, Brown Thrasher, Wood Thrush, Bell Vireo, Warbling Vireo, Prothonotary Warbler, Yellow Warbler, Chat, Eastern Meadowlark, Western Meadowlark, Red-winged Blackbird, Orchard Oriole, Baltimore Oriole, CommonGrackle, Lark Sparrow, and Field Sparrow, furnish 1,233 records of breeding (Fig. 1). The distribution of completed clutches runs from the first third of April to the first third of September. The modal date for completion of clutches is June 1.
South American Element
Twelve species, Eastern Kingbird, Western Kingbird, Scissor-tailed Flycatcher, Great Crested Flycatcher, Yellow-bellied Flycatcher, Traill Flycatcher, Eastern Wood Pewee, Eastern Phoebe, Cardinal, Black-headed Grosbeak, Rose-breasted Grosbeak, and Indigo Bunting, furnish 552 records of breeding (Fig. 1). The curve representing this summary schedule is bimodal, wholly as a result of including the Eastern Phoebe and the Cardinal with this sample.
Relationship of Schedules to Temperature and Precipitation
In outlining the ten categories above, attention has been given to certain similarities and differences in the frequency distributions. A slightly more refined way of comparing the frequency distributions is to relate them to other, seasonally variable phenomena. Figure 1 shows the frequency distributions of egg-laying of these ten categories of birds in terms of the regular changes in mean temperature and mean precipitation characteristic of the environments in which these birds live in the breeding season.
Table 9shows that there are two basic groups of birds according to peak of egg-laying and incidence of precipitation; raptors, birds of Eurasian origin, resident birds, and birds of grassland habitats tend to have their peaks of egg-laying prior to the peak of spring-summer rains, and the other six categories tend to have their peaks of egg-laying occur in the time of spring-summer rains. Regarding temperature, there are four categories of birds; these are evident in the table.
Some of the correspondences deserve comment. Residents and grassland species both breed before the rains come and before mean temperatures reach 70°F., and this correspondence probably results from most of the grassland species being residents. Contrariwise, most birds of Eurasian stocks are residents, but not all residents are of such stocks; the two groups are discrete when mean temperature at breeding is considered. Woodland birds, aerial foragers, and birds of South American evolutionary stocks breed after temperatures surpass 70°F. on the average. Almost all such species are migrants, but many migrants have different temporal characteristics, and the categories thus are shown to be discrete on the basis of temperature at time of breeding.The change through spring and summer of temperature and precipitation delineates the inception and waxing of the growing season of vegetation and of the subsequent arthropod populations, on which most of the birds feed in the breeding season. The temporal characteristics of growing seasons in North America have been treated by Hopkins (1938) and have been related to timing of breeding seasons in Song Sparrows (Passerella melodia) of the Pacific coast of North America (Johnston, 1954).
Significance of Phylogeny to Breeding Schedules
Evidence from a variety of sources demonstrates that timing of breeding seasons is either broadly or specifically genetically-determined. For some species in some situations major environmental variables are paramount in regulating timing of breeding, but in others the innate, regulatory "clock" is less closely tied to conspicuous exogenous stimuli. The work by Miller (1955a, 1955b, 1960) with several species ofZonotrichiastrongly indicates that endogenous timing is most important for these birds, and there is ecological evidence for Song Sparrows that supports the same point (Johnston, 1954, 1956). It is, in any event, possible to treat breeding schedules as species-specific characters, for any one geographic area.
In an attempt to relate a breeding schedule to previous ancestral modes, that is by extension to phylogeny, it is necessary to know how often ancestral adaptations can persist in the face of necessity to adapt to present environmental conditions. It is necessary to know how conservative or how immediately plastic breeding schedules can be. The disadvantage of using available information about configurations of breeding seasons (as shown in Figs. 3 to 9) is that it is extremely difficult to compare visually at one time more than six or eight histograms as to the trenchant similarities and differences regarding times of inception and cessation of breeding, and time of peak egg-laying. It is possible, however, to reduce these three variables to one variable (as described below), which allows the necessary comparisons to be made more easily; this variable may be called thebreeding index.
Calculation of Breeding Index
The chronological year is broken roughly into ten-day intervals numbered 1 to 36. The histogram describing the temporal occurrence of the breeding season of a species in our area usually will lie within intervals 7 to 25. The modal date for completion of clutches is given a value corresponding to the number of ten-dayintervals beyond interval 7 (March 1-10); this describes the modal variable. The date of completion of 83 per cent of all clutches is given a value corresponding to the number of ten-day intervals it lies from interval 11 (April 11-20); this describes the 83 per cent variable (and is a measure of the length of the season in terms of its inception). The breeding index can then be calculated as follows:
I =Xm+Xsd,where:I is the breeding index,Xmis the modal variable, andXsdis the 83 per cent variable.
This is obviously an arbitrary scheme to gain a simple measure of beginning, peak, and end of a breeding season. Other schemes could be devised whereby different absolute values would be involved, but the relative nature of the results would be preserved. The values under the present system for 73 species of Kansan birds run from -5 to +22; early modal dates and cessation to breeding give low values, late dates high values.
Within this framework there are other, presumably subordinate, factors that influence the values of breeding indices, as follows:
1. Migratory habit. Any migrant tends to arrive on breeding grounds relatively late, hence migrants ordinarily have higher index values than do residents.
2. Colonial breeding. The strong synchrony of colonially-breeding species tends to move the modal egg-date toward the time of inception of breeding; as a result colonially-breeding species probably have lower index values than they would have if not colonial.
3. Single-broodedness. Species having only one brood per season tend to have shorter seasons than double-brooded species, and their index values tend to be lower than those of double-brooded species.
Migratory habit unquestionably has considerable influence on index values in some species. It is not, however, as important as other matters, such as the condition of the food substratum or sensitivity of the pituitary-gonadal mechanism, in determining timing and mode of breeding activity. The schedule of the Purple Martin is the extreme example showing that time of spring arrival on breeding grounds is not necessarily related to time of inception of breeding. It should be emphasized that the factors leading to northward migratory movement may be involved in timing of the annual gonadal and reproductive cycle.
Figure 2 presents a graphic summary of values of breedingindices for many groups of Kansan birds. The values for species of a given family have been linked by a horizontal line. The length of this line is proportional to the degree to which the index values for the species concerned resemble one another. Note that the plottings for the Picidae, Corvidae, Turdidae, Tyrannidae, and Icteridae each contain one point that is well-removed from a cluster of points. This can be interpreted as a measure of the frequency of adaptive plasticity versus adaptive conservatism; five of the 24 plottings show a plastic character, 19 a conservative. There are 26 plottings that show temporal consistency, all of which may be taken as evidence of adaptive (or relictual) conservatism of the species in question.
Fig. 2.—Breeding indices for Kansan birds.Fig.2.—Breeding indices for Kansan birds. Vertical hash-marks indicate the value of breeding index for a given species; horizontal lines show the range of values of breeding index for families and orders.
Conclusion
Such patterns of breeding chronology support the idea that seasonal response to the necessities of breeding is conservative more often than plastic. Most students of breeding schedules believe that since these are highly adaptive, they must also be capable of flexibility to meet variable environments within the range of the species. Such thinking receives support when different geographic localities are considered for one species (Johnston, 1954), or when specific features of a special environment are considered (see Miller, 1960; Johnston, 1956).
Yet, if one, relatively restricted locality is considered, as in the present study, evidence of a conservative characteristic in breeding schedules can be detected. This conservatism may result from the historic genetic "burden" of the species; that is to say, previous adaptive peaks may in part be evident in the matrix of contemporary adaptation. Adaptive relicts of morphological nature have been many times documented, but characteristics associated with seasonality and timing schedules have not.
In any event, genetic relationships are evident in the configuration of breeding seasons of many species here treated. Thus, any consideration of variation in breeding schedules must be sensitive to the limits, whether broad or restricting, that the heritage of a species sets on its present chronological adaptation.
Regulation of Breeding Schedules
Regulation of breeding schedules in birds always involves some exogenous, environmental timing or triggering mechanism. Broad limits to functional reproductive activity seem to be set by the photoperiod—neuroendocrine system. This basic, predominately extra-equatorial, regulator can be ignored by temperate-zone species only if they possess chronological adaptation to special, aperiodic environmental conditions, as does the Red Crossbill (Loxia curvirostra; see McCabe and McCabe, 1933; H. B. Tordoff, ms.), for which the chief consideration seems to be availability of conifer seeds. Environmental phonomena otherwise known to trigger breeding activity include rainfall (Davis, 1953; Williamson, 1956), presence of suitable nesting material (Marshall and Disney, 1957; Lehrman, 1958), temperature (Nice, 1937), and presence of a mate (Lehrman, Brody, and Wortis, 1961). Such regulators, or environmental oscillators, are the "phasing factors" of the physiologic clock that dictate the temporal occurrence of primary reproductive activity.
None of the regulators mentioned above has been specifically investigated for any Kansan bird, but it is reasonable to suppose that, in these temperate-zone species, the photoperiod is the most important general phasing factor in seasonal breeding. Although gonadal response and seasonal restriction of breeding are set by the photoperiod, specific temporal relationships are dictated by more immediate environmental variables.
Table 9.—Relationship Between Environmental Factors and Timing of Breeding in Birds of KansasOccurrence of Peak of Egg-layingWhen Precipitation is:When Mean Temperature (F.) is:LightHeavy< 55°< 70°± 70°> 70°RaptorsxxO. W. ElementxxResidentsxxGrassland speciesxxMarshland speciesxxN. Amer. ElementxxMigrantsxxWoodland speciesxxAerial foragersxxS. Amer. Elementxx
Table 9.—Relationship Between Environmental Factors and Timing of Breeding in Birds of Kansas
Table 9, as already noted, shows the gross relationships between certain groups of birds, certain arbitrary indicators of seasonal temperature-humidity conditions bearing significantly on the growing season, and occurrence in time of peak of egg-laying by the birds involved. Some species and groups of Kansan birds breed chiefly under cool-dry environmental conditions, and some under warm-wet environmental conditions. Within each of these categories some variation occurs. Thus, raptors and boreally-adapted species (the Eurasian zoogeographic element) breed under cool conditions prior to rains, and residents and grassland species breed under slightly warmer conditions prior to rains; limnic species, species derived from North American evolutionary stocks, and migrants tend to breed in the cooler segment of the warm-wet period, and woodland birds, aerial foragers, and species derived from South American evolutionary stocks tend to breed in the warmer segment of the warm-wet period.
So much, then, for relationships between birds and their environmentsat a descriptive level. It would be useful at this point to examine how environmental variables relate to timing of breeding. Certain independent lines of investigation indicate that birds have a well-developed internal timing device; most convincing is the work of Schmidt-Koenig (1960) and the others who have shown that the endogenous clock of birds can be shifted in its periodicity forward or backward in time. This and much other evidence (see Brown, 1960) indicate that many fundamental periodic regulators are extrinsic to the animal; it is thus permissible for present purposes to consider any expression of variation in timing as dependent on environmental oscillators. It is not hereby meant to ignore the fact that differential responses to dominant environmental variables occur within a species, indicating endogenous control over timing of breeding. The work by Miller (1960:518) with three populations of the White-crowned Sparrow, revealing innately different responses to vernal photoperiodic increase, is especially important in this regard. For the moment, however, we may consider exogenous controls only.
Any exogenous control, or environmental variable, can be looked on simply as a timing oscillator. Such variables show regular or irregular periodic activity, and the independent actions as a whole result in the more-or-less variable annual schedule of breeding for any species at any one place. It would seem that some oscillators are linked to one another, but there is a real question concerning the over-all degree to which linkage is present. It is significant that frequency distributions of breeding activity of various species and groups of birds take on the shape of a skewed normal curve. The more information is added to such distributions, the more nearly they approach being wholly normal, with irregularities tending to disappear. This kind of response itself is evidence that most of the variables influencing the distribution are not mutually linked.
This conclusion is warranted if we examine what would happen to frequency distributions if the variables or oscillators regulating timing were linked. The frequency distribution of breeding activity in birds is described by a nonlinear curve (a normal distribution is nonlinear). Let us assume that each of the environmental variables is a nonlinear oscillator, as is probable. A set of nonlinear oscillators mutually entrained or coupled and operating with reference to a given phenomenon would result in that phenomenon being described by a frequency distribution much more stable than if it were regulated by any one oscillator alone. However, the frequency distribution of a setof coupled nonlinear oscillators is non-normal (Wiener, 1958).
We do not obtain such distributions in describing breeding activity, so we may say that the oscillators regulating such activity are not coupled. Present distribution, habitat preference, residency status, foraging adaptation, previous zoogeographic history, and relicts of ancestral adaptation, all bear on the character of the breeding schedule of any bird species. The emphasis above on multiple regulation of breeding schedules conceivably reflects the true picture, but any such emphasis is made at the expense of taking one factor as basic, or reducing the many to one, in order to manufacture simplicity.
ACCOUNTS OF SPECIES
In each account below information is given concerning status, habitat, geographic distribution, seasonal occurrence, schedule of egg-laying, number of eggs laid, and sites of nests, as these pertain to Kansas, unless otherwise stated. The ways in which some of these points were elucidated are as follows.
1.—Breeding schedule. Frequency distributions of egg-laying in time are calculated on the basis of dates of completed clutches, as described earlier (p. 588). Any event in the series of actions of nesting—nestbuilding, egg-laying, incubation, brooding, feeding young out of nests—can be manipulated by adding or subtracting days to or from the date of record to yield the probable date of completion of the clutch. The resulting data are grouped into class intervals of ten days. Extreme dates here given for egg-laying may be as much as nine days off in accuracy, but the error does not often exceed five days. Extreme dates indicated here may be taken as actual or predicted extremes. The raw data used are on file at the Museum of Natural History and are available for use by any qualified individual.
2.—Dates of occurrence. First and last annual occurrences in the State for migrant species are indicated by both a range of dates and a median date. Twenty to 30 dates of first observation in spring are available for most of the common species, and 10 to 20 dates of last observation in autumn are at hand for such species. The median dates, earlier than and subsequent to which an equal number of observations are available, are reliable indicators of the dates on which a species is likely to be seen first in the State in an average year.
3.—Clutch-size. Information on number of eggs is given for each species according to the mode, followed by the mean, the range, and the size of the sample.
4.—Distribution in Kansas. Information on distribution in the breeding season within the borders of Kansas is given in accounts below chiefly by reference to one or more counties of the State. Location of counties can be made by referring to Figure 10.
Pied-billed Grebe:Podilymbus podiceps podiceps(Linnaeus).—This is a common but local summer resident, in and on ponds, marshes, streams, ditches, and lakes. The species can be seen in the State at any time, but usually arrives in the period March 1 to April 13 (the median is March 21), and departs southward in the period October 13 to November 18 (the median is October 24).
Breeding schedule.—Nineteen records of breeding span the period May 1 to June 30; the modal date for egg-laying is May 15.
Number of eggs.—Clutch-size is 4 to 10 eggs.
Nests are floating masses of marsh vegetation (cattail, smartweed, duckweed, filamentous green algae, and the like), kept green on top by addition of fresh material, in or at the edge of emergent marsh vegetation.
Double-crested Cormorant:Phalacrocorax auritus auritus(Lesson).—This is a transient, but has been found nesting on one occasion in Barton County (Tordoff, 1956:311).
Breeding schedule.—Eggs were laid in July and August in the one known nesting effort.
Number of eggs.—Clutch-size is 2 to 4 eggs (Davie, 1898).
Great Blue Heron:Ardea herodiasLinnaeus.—This common summer resident nests in tall trees along rivers, streams, and marshes. The sector of greatest abundance is the Flint Hills.A. h. herodiasLinnaeus occurs in extreme northeastern Kansas,A. h. wardiRidgway breeds in southeastern Kansas, andA. h. treganzaiCourt breeds in western Kansas; specimens showing intermediate morphology have been taken from the central part of the State. Occurrence in time, exclusive of the few that overwinter in Kansas, is shown inTable 10.
Breeding schedule.—Seventy-seven records of breeding span the period March 1 to April 30 (Fig. 3); the modal date of egg-laying is April 5.
Number of eggs.—Clutch-size is 4 eggs (4.4, 3-6; 36).
Nests are placed in crotches of sycamore, cottonwood, elm, hackberry, oak, and walnut, from 30 to 60 feet high; the average height is about 40 feet.
Table 10.—Occurrence in Time of Summer Resident Herons in KansasSpeciesArrivalDepartureRangeMedianRangeMedianGreat Blue HeronFeb. 4-Apr. 8Mar. 20Oct. 10-Nov. 29Oct. 23Green HeronMar. 29-May 4Apr. 27Sept. 1-Oct. 30Sept. 9Common EgretApr. 8-May 12Apr. 2Sept. 4-Sept. 30Sept. 21Black-crowned Night HeronMar. 27-May 18Apr. 25Sept. 10-Nov. 11Sept. 25Yellow-crowned Night HeronApr. 15-May 18Apr. 27................American BitternApr. 4-May 9May 1Oct. 6-Dec. 12Oct. 16Least BitternApr. 9-May 22Apr. 8Oct. 24........
Table 10.—Occurrence in Time of Summer Resident Herons in Kansas
Green Heron:Butorides virescens virescens(Linnaeus).—This is a common summer resident about streams, lakes, and marshes throughout the State. Some characteristics of the temporal occurrence of this species are indicated inTable 10.
Breeding schedule.—Twenty-eight records of breeding span the period April 21 to June 20 (Fig. 3); the modal date of completion of clutches is May 5.
Number of eggs.—Clutch-size is 3 eggs (3.1, 3-5; 17).
Nests are placed about 10 feet high (two to 35 feet) in willow, cottonwood, elm, and the like.
Little Blue Heron:Florida caerulea caerulea(Linnaeus).—This is chiefly a postbreeding summer visitant, but there is one record of breeding in Finney County (Tordoff, 1956:312).
Breeding schedule.—There is no information on breeding schedule in Kansas or in adjacent areas.
Number of eggs.—Clutch-size is 2 to 4 eggs (Davie, 1898).
Nests are placed in trees and bushes at various heights above the ground.
Common Egret:Casmerodius albus egretta(Gmelin).—This is a postbreeding summer visitant, but has been found nesting once in Cowley County (Johnston, 1960:10). Occurrence in time is listed inTable 10.
Breeding schedule.—There is no information on breeding schedule in Kansas.
Number of eggs.—Clutch-size is 2 to 4 eggs (Davie, 1898).
Nests are placed in trees, usually above 20 feet in height; the one instance of nesting in the State was within a colony of Great Blue Herons.
Snowy Egret:Leucophoyx thula thula(Molina).—This postbreeding summer visitant has been found nesting once in Finney County (Tordoff, 1956:312).
Breeding schedule.—There is no information on breeding schedule in the State.
Number of eggs.—Clutch-size is 2 to 5 eggs (Davie, 1898).
Nests in Kansas are placed among those of Great Blue Herons.
Black-crowned Night Heron:Nycticorax nycticorax hoactli(Gmelin).—This is a locally common summer resident around marshes and riparian habitats. Characteristics of the occurrence of the species in time are given inTable 10.
Breeding schedule.—Eggs are laid in the period May 1 to August 10.
Number of eggs.—Clutch-size is about 4 eggs.
Nests are placed at medium elevations in riparian trees, in Kansas chiefly cottonwood, or in beds of emergent marsh vegetation.
Yellow-crowned Night Heron:Nyctanassa violacea violacea(Linnaeus).—This is a local summer resident in riparian habitats, chiefly in southeastern Kansas. Specimens taken in the breeding season and records of nesting come from Meade, Stafford, Doniphan, Douglas, Greenwood, Woodson, Labette, and Cherokee counties. Characteristics ofoccurrence in time in Kansas are shown inTable 10.Breeding schedule.—Eggs are laid in May and June.
Number of eggs.—Clutch-size is about 4 eggs.
Nests are placed in riparian trees.
Least Bittern:Ixobrychus exilis exilis(Gmelin).—This is a local summer resident in marshland. Characteristics of its occurrence in time are indicated inTable 10.
Breeding schedule.—Eleven records of breeding span the period May 21 to July 20; the modal date of egg-laying seems to be in the first week of June.
Number of eggs.—Clutch-size is about 4 eggs.
Nests are placed in dense emergent vegetation a few inches to a foot above the surface of the water.
American Bittern:Botaurus lentiginosus(Rackett).—This is a local summer resident in marshes and heavy grassland. The species occurs temporally according to characteristics as listed inTable 10.
Breeding schedule.—Eggs are laid in May and probably in June.
Number of eggs.—Clutch-size is 3 or 4 eggs.
Nests are placed on the ground in heavy cover.
White-faced Ibis:Plegadis chihi(Vieillot).—This is a local summer resident in marshland; actual records of breeding come only from Barton County (Nossaman, 1952:7; Zuvanich, 1963; M. Schwilling, personal communication, July, 1962). The species has been recorded in the State from April 17 to October 6.
Breeding schedule.—Twenty-five breeding records are for June and early July.
Number of eggs.—Clutch-size is about 4 eggs (3.9, 3-4; 24).
Nests are placed in emergent marsh vegetation near the surface of the water, in Barton County in extensive cattail beds harboring also Black-crowned Night Herons.
Mallard:Anas platyrhynchos platyrhynchosLinnaeus.—This is a local summer resident around marshes. The time of greatest abundance is October to April, but most birds move north for breeding.
Breeding schedule.—Fifteen records of breeding span the period April 1 to June 10; the modal date of egg-laying is in the first ten days of May.
Number of eggs.—Clutch-size varies widely; first clutches are of about 12 eggs. Brood sizes vary from 3 to 12 individuals in Kansas.
Nests are placed on the ground surface, in pasture grasses, marsh grasses, cattail, sedge, and smartweed.
Pintail:Anas acutaLinnaeus.—This is a local summer resident in marshland. The time of greatest abundance is from September to May, but most birds move north for breeding.
Breeding schedule.—Eleven records of breeding span the period April 21 to June 10; the peak of egg-laying seems to be in the period May 1 to 10.
Number of eggs.—Clutch-size is around 10 eggs. Brood sizes vary from 3 to 8 individuals in Kansas.
Nests are placed on the ground surface, in cover of marsh grass,cattail, or sedge.
Blue-winged Teal:Anas discors discorsLinnaeus.—This summer resident is locally common around marshes and ponds. The species arrives in spring in the period March 9 to April 5 (the median is March 23); birds are last seen sometime between October 7 and November 26 (the median is October 20).
Breeding schedule.—Twenty-two records of breeding span the period May 1 to May 30; the peak of egg-laying is around May 15. It is doubtful that the present data indicate the full extent of the egg-season in this duck.
Number of eggs.—Clutch-size is 8 to 12 eggs.
Nests are placed on the ground surface, in cover of grasses, cattail and sedges.
Shoveler:Anas clypeataLinnaeus.—This is an irregular and local summer resident, around marshes. Most individuals seen in the State are passage migrants. Breeding records are from Barton and Finney counties.
Breeding schedule.—Seasonal limits are unknown for the Shoveler in Kansas.
Number of eggs.—Clutch-size is about 8 eggs (Davie, 1898).
Nests are placed on the ground surface in cover of marsh vegetation.
Wood Duck:Aix sponsa(Linnaeus).—This is an uncommon summer resident around wooded streams and ponds in eastern Kansas. Nesting records and specimens taken in the breeding season come from east of stations in Pottawatomie, Coffey, and Woodson counties. Most nesting records at present come from the Marais des Cygnes Wildlife Refuge, Linn County. The species is present in the State from March 5 to December 8.
Breeding schedule.—Eleven records of breeding span the period March 21 to May 10; the peak of egg-laying is probably in mid-April. The present data are inadequate for showing the full span of the breeding season.
Number of eggs.—Clutch-size is around 15 eggs, varying from 10 to 23 in the sample at hand.
Nests are placed in crevices and hollows in trees near water, 10 to 70 feet high.
Redhead:Aythya americana(Eyton).—This duck nested at Cheyenne Bottoms, Barton County, 1962: 9 eggs found May 31 (M. Schwilling); also reported to have nested at Cheyenne Bottoms about 1928 (Tordoff, 1956:316).
Canvasback:Aythya valisineria(Wilson).—This duck nested at Cheyenne Bottoms, Barton County, 1962: 14 eggs found June 20 (M. Schwilling).
Ruddy Duck:Oxyura jamaicensis rubida(Wilson).—This is a local summer resident in marshland; numbers seem generally higher in western than in eastern Kansas. The season of greatest abundance is March through November, but numbers are conspicuously reduced in midsummer.
Breeding schedule.—Eggs are known to be laid in May and June.
Number of eggs.—Clutch-size is about 10 eggs (Davie, 1898).
Nests are placed near the edge of water, either in or on emergent marsh vegetation; nests of other marshland birds, such as coots, are sometimes appropriated (Davie, 1898).
Turkey Vulture:Cathartes aura teterFriedmann.—This summer resident is common throughout Kansas. Occurrence in time is indicated inTable 11.
Breeding schedule.—Fifteen records of breeding span the periodApril 21 to June 10; earlier records will doubtless be found, to judge from the frequency distribution of the present sample. The peak of egg-laying is perhaps around May 1.
Number of eggs.—Clutch-size is 2 eggs (1.8, 1-2; 12).
Nests are placed in holes and crevices in trees and cliffs, on rocky ledges, and the like.