Fig. 7.Possible distribution in Illinoian (inset) and Sangamonian times of the ancestor of theSorexvagrans-ornatus-longirostris-veraepaciscomplex. Approximate southern boundary of Illinoian glaciation marked by heavy line.In the ensuing Sangamonian interglacial age all glaciers retreated or disappeared thereby opening up extensive areas in the north and in the higher mountains which were occupied by a boreal fauna, includingS. vagrans. Concurrently the Great Basin, and probably also much of the Columbian Plateau, became dry, and desert conditions developed, perhaps much as they are today. Increasing aridity eliminated shrew habitat in most places between the Rocky Mountains and the Sierra Nevada-Cascade mountain chain with the result that the geographic range of the species resembled an inverted "U", one arm lying along the Rocky Mountains and the other along the Cascade-Sierra Nevada axis; the connection between the two arms was in British Columbia (seefig. 7). At presentSorex vagransdoes occur in isolated places in the Great Basin, but its existence there is tenuous and seemingly dependent upon the occurrence of permanent water such as Ruby Lake and Reese River. With such an arrangement as this it can readily be seen that gene flow between the eastern and western arms of the "U" would be greatly reduced by distance; consequently differentiation between the two might be expected.Fig. 8.Possible distribution ofSorexvagransat two different times in the Wisconsinan Age. Left, early Wisconsinan; right, mid-Wisconsinan.Wisconsinan glaciation again rendered Canada uninhabitable, and it is quite possible that extensive areas in the Rocky Mountains, the Cascades and the Sierra Nevada were heavily glaciated. With the elimination of the northern part of the "U", the eastern andwestern arms became isolated, if not by the width of the Columbian Plateau at least by the glaciated Cascade Mountains. At the same time extensive areas on the Colorado Plateau and much of the area south to the Mexican highlands were again occupied by the species. Finally the Great Basin, again being well-watered, provided suitable habitat for, and was reoccupied by,Sorex vagrans(seefig. 8). This reoccupation of the Great Basin took place probably from the Colorado Plateau and mountains of Arizona and Utah, since the present day shrews of the speciesS. vagransin the Great Basin closely resemble Rocky Mountain shrews but differ markedly from the large endemic subspecies of the Pacific Coast.Finally, with the waning of Wisconsinan ice, the species again was able to occupy northern and montane areas as it had during Sangamonian times. Again dessication of the Great Basin caused drastic restriction of shrew habitat. The small, marsh-dwelling kind of wandering shrew which had developed there around the lakes of Wisconsinan time occupied suitable habitat all the way to the Pacific coast where its range came into contact with that of the western arm of the Sangamonian "U."-pattern of shrew distribution (seefig. 9). The animals of this western segment and the new arrivals from the east were by this time so different from one another that the two kinds lived in the same areas without interbreeding. The descendants of the original western arm now are known asSorex vagrans sonomae,S. v. pacificus,S. v. yaquinae, andS. v. bairdi. The newcomers from the east are known asS. v. vagrans,S. v. halicoetes,S. v. paludivagusandS. v. vancouverensis.In addition to occupying the Pacific Coast from San Francisco Bay north to the Fraser Delta, the Great Basin subspecies populated the Columbia Plateau and the western foothills of the central and northern Rockies. By so doing that subspecies came into secondary contact with its own parent stock with which it was still in reproductive continuity in Utah. In some places in British Columbia differentiation between the two kinds had proceeded to such an extent that some reproductive isolation was effected, but in many other places the two interbred. The Rocky Mountain form spread north and west and occupied the Cascades and coastal lowlands in southwestern British Columbia and in Washington. Here the differentiation between the Rocky Mountain subspecies and the Great Basin subspecies was great enough to cause complete reproductive isolation.Fig. 9.Probable changes in the distribution ofSorex vagransconcurrent with and following the dissipation of Wisconsinan ice. Dark arrows in Washington, Idaho, Oregon, and California, showsS. v. vagrans.Deglaciation of the Sierra Nevada opened it up for reoccupation from the east bySorex vagranss of the Great Basin. In response to the montane environment the subspeciesobscuroides, resembling the subspeciesobscurusof the Rockies, developed.Desiccation of the intermontane parts of New Mexico, Arizona, and Chihuahua, left "marooned" populations ofSorex vagranson suitable mountain ranges. In this waySorex vagrans orizabaemay have been isolated in southern Mexico. The isolated populations of Arizona and New Mexico differentiatedin situinto the subspeciesmonticolaandneomexicanus.Western Canada and Alaska were populated by shrews which originated in the habitable parts of the Rocky Mountains and Colorado Plateau during Wisconsinan time (as opposed to shrews originating, as subspecies, in the Great Basin or on the Pacific Coast). These shrews differentiated into the currently recognized subspecies of the west coast and coastal islands of British Columbia and Alaska in response to the different environments in these places, many of which were isolated; the subspeciesisolatus,mixtus,setosus,longicauda,elassodon,prevostensis,malitiosus, andalaskensisare thought to have originated in this fashion after the areas now occupied by them were freed of Wisconsinan ice.This group of shrews from the Rocky Mountains probably came into contact with the Pacific coastal segment of the species somewhere in northwestern Oregon. The clinal decrease in size fromS. v. pacificustoS. v. setosusseems steepest in this area. Upon the establishment of this contact reproductive continuity was resumed, probably because the temporal separation of the two stocks involved was not so great as, say, that betweenS. v. vagransandS. v. pacificus, and in addition the morphological differentiation was not so great.On the eastern side of the Rockies the montane stock moved northeastward, occupying suitable territory opened up by the dissolution of the Laurentide ice sheet. Still later changes in the character of the northern plains owing to desiccation divided the range of the species and isolatedS. v. soperiin Manitoba and central Saskatchewan and a population ofS. v. obscurus, in the Cypress Hills. A number of semi-isolated stocks in central Montana became differentiated as a recognizable subspecies there.A number of other boreal mammals have geographic ranges which resemble that ofSorex vagrans, except that the geographic ranges of subspecies do not overlap. Because of the general similaritiesof these geographic ranges, it is pertinent to examine the reasons suggested by students to account for the present geographic distributions of some of these other boreal species.The red squirrel genus,Tamiasciurus, has a Rocky Mountain (and northern coniferous forest) species,T. hudsonicus, that occurs all along the Rocky Mountain chain and northward into Alaska. In the Cascade Mountains of Washington and British Columbia this species meets the range of a well marked western species,T. douglasii, with no evidence of intergradation. Dalquest (1948:86) attributes the divergence of the two species to separation in a glacial age but feels that the degree of difference between the two is too great to have all taken place during the Wisconsinan. Perhaps he has overemphasized the importance of the differences between the two, but, be that as it may, it seems that the two kinds differentiated during a glacial age when they were isolated, perhaps by ice on the Cascades into a coastal population and an inland population. One difference between the distribution of the red squirrels and vagrant shrew is that the squirrel of the Sierra Nevada is the species of the Pacific Coast, whereas the vagrant shrew of the Sierra Nevada was derived from the Great Basin population, which in turn was derived from the Rocky Mountain kind. Red squirrels do not occur on any of the boreal montane "islands" of Nevada. During the pluvial periods when hydrosere-loving shrews populated the Great Basin, that region may have been a treeless grassland. Vagrant shrews, then as now, probably depended on hydrosere communities, while red squirrels required trees. Therefore the shrews were able to traverse the Great Basin, while the Sierran red squirrels were of necessity derived from the coastal population.The ecological requirements of jumping mice, genusZapus, and the subspecies ofSorex vagransthat dwell in hydroseres are essentially similar. The speciesZapus princepslives in the Rocky Mountains, the Great Basin, the Sierra Nevada, and north to Yukon (Krutzsch, 1954:395). Its geographic range is similar to that of the montane and basin segments ofS. vagrans. The speciesZ. trinotatusoccurs along the Pacific coast and in the Cascades north to southwestern British Columbia. Its distribution thus coincides in general with that of the large red coastal subspecies ofS. vagrans. Krutzsch (1954:368-369) thought that these two kinds of jumping mice were first separated by the formation of the Cascade Mountains and the Sierra Nevada and finally by Pleistocene glaciation. The Sierran jumping mouse (Zapus princeps), as is the Sierran vagrant shrew, is more closely related to the jumping mouse of theGreat Basin and of the Rocky Mountains than it is to the jumping mouse (Z. trinotatus) of the Pacific Coast, just as the Sierran vagrant shrew is related to the shrew of the Great Basin and Rocky Mountains. The jumping mouse also is limited in its distribution by hydrosere communities, not by forests.In western North America there are two species of water or marsh shrews:Sorex palustrisandS. bendiri. They have been placed in separate subgenera, but, as pointed out beyond, are closely related and here are placed in the same subgenus. The speciespalustrisis found throughout the Rocky Mountains, north into Alaska, across the Great Basin into the Sierra Nevada, and west to the Pacific coast in Washington. The speciesbendiriis found from northwestern California north along the Pacific coast to southwestern British Columbia and east to the Cascades. Where the ranges of the two species overlap in western Washington they do not interbreed so far as is known, and are somewhat different in their ecology,bendiribeing a lowland, andpalustrisbeing a montane, species. The two species probably were separated in a glacial period as seems to have been the case with the wandering shrews. Also, the water shrew of the Sierra Nevada is derived from that of the Great Basin and Rocky Mountains.Sorex palustrisis tied closely in its distribution to hydrosere communities and is not dependent upon the presence of forests.Red-backed mice, genusClethrionomys, occur throughout the Rocky Mountains and west to the Cascades in Washington as the speciesC. gapperi. The speciesC. californicusis found along the Pacific Coast from California north to the Olympic Peninsula. Where the ranges of the two species meet in Washington they seem not to intergrade. In some glacial interval these two species may have evolved in the same manner as has been described for the species ofZapusand those ofTamiasciurus. NoClethrionomysare found in the Sierra Nevada, nor are red-backed mice found in the boreal islands of the Great Basin. It is not known whyClethrionomys californicusdoes not occur in the Sierra Nevada. Some boreal birds have distributional patterns similar to those of the mammalian examples cited above. One kind of sapsucker,Sphyrapicus varius nuchalis, occurs in the Rocky Mountains north into British Columbia and west to the Cascades and Sierra Nevada. A related kind,S. varius ruber, occurs along the Pacific Coast from California north into British Columbia. Recently Howell (1952) has shown that some intergradation takes place betweenruberandnuchalisin Washington and British Columbia, although they do not intergradefreely. Previously the two kinds were thought not to intergrade and were regarded as two species. The two kinds intergrade also in northeastern California, although in that stateS. v. daggeti, rather thanS. v. ruber, is involved in the intergradation. Howell considered the two kinds to be conspecific with one another as well as with the easternS. varius. He attributed a measure of the distinctness ofnuchalisandruberto their separation during a glacial period, but felt that the separation was much older than Wisconsinan. Whatever the time of separation, the pattern seems clear:nuchalisandruber(as well asvarius) were separated into montane, coastal, and eastern segments respectively, probably by glaciation (it seems to me in the Pleistocene), and have since re-established contact with one another.The grouse genusDendrogapusis divided into a Great Basin species,D. obscurus, which extends northward into British Columbia, and a Rocky Mountain species,D. fuliginosus, that is found in the Sierra Nevada and northward along the coast and Cascades into British Columbia. Although the two kinds have at times been considered conspecific, they differ in voice, hooting mechanism, and characters of the downy young, and so far no actual intergradation between the two has been shown (Grinnell and Miller, 1944:113). These grouse thus seem to offer additional evidence for a Pleistocene, possibly Wisconsinan, separation of the boreal fauna into a Rocky Mountain and a Pacific coastal segment.A notable sidelight on these data is the frequency with which species in the Sierra Nevada have their closest relatives in the Rocky Mountains, rather than in the geographically nearer Cascades or coastal areas. This similarity in fauna of the Sierra Nevada and the Rockies was noted long ago by Merriam (1899:86).RELATIONSHIPS WITH OTHER SPECIESDuring the Sangamonian interval, isolated segments of the once widespread ancestralSorex vagransquite possibly persisted in such places as the Sierra Nevada, coastal southern California, the mountains of Arizona, New Mexico, and southern Mexico, and in the Black Hills (seefig. 6). One might expect that by Wisconsinan time these populations would have become reproductively isolated from their parent stock. They would therefore have remained specifically distinct when WisconsinanSorex vagrans, reoccupied these outlying areas, and may still be found isolated in places peripheral to the range of the ancestral species.Fig. 10.Probable distribution ofS.veraepacis,S. longirostris, and theS. ornatusgroup (stipple) and of their Wisconsinan ancestors (lines). Heavy line indicates limits of Wisconsinan glaciation.In fact, we do find species closely related toSorex vagransin just such places today (fig. 10). ProbablySorex ornatus, including members of theornatusgroup such asS. trigonirostris,S. sinuosus,S. willeti,S. tenellus, andS. nanus, and alsoS. veraepacis, arose by separation from the ancestralvagransstock in Sangamonian time. Probably the easternS. longirostrisarose in a like manner. The ancestor ofS. ornatusmay have been isolated in southwestern California during Sangamonian time, spread north and south during the Wisconsinan age, and afterward given rise toS. trigonirostrisand the modernS. ornatuscomplex of California and Baja California. In at least one place reproductive isolation betweenornatusand the invadingS. vagranshas broken down (Rudd, 1953); the place is a salt marsh along San Pablo Bay, where a hybrid population betweenS. vagransandS. sinuosus, anornatusderivative, has formed.Sorex tenellusmay have been isolated in the Sierra Nevada in the Sangamonianinterval, moved into the valleys east of the mountains during the Wisconsinan age, and become restricted to its present range since the retreat of the last ice.Sorex nanusmay have occurred in the Black Hills and isolated mountains of Arizona and New Mexico during the Sangamonian interval and remained in these general areas during the Wisconsinan age. Its present range is peripheral to the main body of the Rockies and the Colorado Plateau.The eastern speciesSorex longirostrishas many similarities with shrews of theornatus-vagransstock.S. l. longirostrisis close in many ways toS. nanus. Indeed, the differences between the speciesS. nanus,S. ornatus, andS. longirostrisseem to me to be of the same magnitude and indicate a similar period of differentiation from a common ancestor. The ancestor ofS. longirostrismay have gained access to the eastern United States in the Illinoian Ageviathe northern Great Plains south of the glacial boundary (fig. 7). The ancestor ofSorex veraepacisof southern Mexico probably reached that area in Illinoian time as part of the ancestralvagransstock and probably attained its differentiation during the Sangamonian interval.All the kinds of shrews so far discussed, including theS. vagranscomplex, might thus be thought of as having had a common ancestor in the Illinoian Age. This entire group of shrews has the third unicuspid smaller than the fourth, a pigmented ridge from the apex to the cingulum of each upper unicuspid, and, in most individuals, lacks a post-mandibular foramen in the lower jaw (Findley, 1953:636-637). The pigment is not always prominent inS. longirostris.Two other species of North American shrews,Sorex palustris, the water shrew, andSorex bendiri, the marsh shrew, show these three characters to a greater or lesser degree, and it seems that these two species and thevagrans-ornatus-veraepacisgroup had a common ancestor, probably before Illinoian time for reasons stated beyond. I judge, however, that far from being subgenerically distinct as they have been considered to be,S. palustrisandS. bendiriare actually closely related species of the same subgenus and may have differentiated from one another because of separation into eastern (palustris) and western (bendiri) segments in the Sangamonian interval, much as has been postulated concerning the eastern and western stocks ofSorex vagrans. Indeed, Jackson (1928:192) has noted that in the Pacific northwest the characters of the two kinds approach one another and become differences of degree only.The widespread speciesSorex cinereusresembles all the foregoing species in the ridges on the unicuspid teeth and in the lack of a post-mandibular foramen, but differs from those other species inhaving the third upper unicuspid larger than the fourth. The subspeciesS. cinereus ohionensis, however, often has the sizes of these teeth reversed. WithS. cinereusI includeS. preblei(eastern Oregon) andS. lyelli(Sierra Nevada), both obviously closely related tocinereusas Jackson (1928:37) recognized when he included them in thecinereusgroup.Sorex milleri(Coahuila and central western Nuevo Leon) seems to me to resembleS. cinereusmore than it does other species of North AmericanSorex, and I judge that it also belongs to thecinereusgroup.Sorex cinereusand its close relatives seem more closely related to the species which have thus far been discussed than they do to such other North American species asS. arcticus,S. fumeus,S. trowbridgii,S. merriami, and the members of theS. saussureigroup; most of these five species last mentioned possess a post-mandibular foramen, lack pigmented unicuspid ridges, and have the third unicuspid larger than the fourth. Because of the morphological resemblances mentioned above, it seems likely to me thatS. cinereusand thevagrans-ornatus-veraepacis-palustriscomplex had a common ancestor in early Pleistocene time.Sorex cinereushas recently been considered to be conspecific with the Old WorldS. caecutiensLaxmann (Van den Brink, 1953) which name, being the older, would apply to the circumpolar species.Hibbard (1944:719) recoveredS. cinereusand a species ofNeosorex(a name formerly applied to the water shrew) from the Pleistocene (late Kansan) Cudahy Fauna. This indicates that the ancestors of the modernS. cinereusand of the water shrew had diverged from one another before that time. Brown (1908:172) recordedS. cinereusandS. obscurusfrom the Conard Fissure in Arkansas. These materials were deposited probably at a later time than was the Cudahy Fauna. TheS. obscurusfrom Conard Fissure probably represents the ancestralS. vagransstock which I think reached eastern United States in Illinoian time and gave rise toS. longirostris. The Conard Fissure material was deposited at a time (Illinoian?) when northern faunas extended farther south than they do today.All of the species mentioned as having structural characters in common withS. vagransseem to have arisen from a common ancestor which had already differentiated from the ancestor of such species asS. arcticus,S. saussurei, and others. Consequently all are here included in a single subgenus. The oldest generic name applied to a shrew of this group, other than the nameSorex, isOtisorexDeKay, 1842, type speciesOtisorex platyrhinusDeKay, asynonym ofSorex cinereus. The subgenus can be characterized as follows.SubgenusOtisorexDeKay1842.OtisorexDeKay, Zoology of New York, pt. 1, Mammalia, p. 22, and pl. 5, fig. 1. Type,Otisorex platyrhinusDeKay (=Sorex cinereusKerr).Third unicuspid usually smaller than fourth; upper unicuspids usually with pigmented ridge extending from apices medially to cingula, uninterrupted by antero-posterior groove; post-mandibular foramen usually absent. Includes the speciesS. cinereus,S. longirostris,S. vagrans,S. ornatus,S. tenellus,S. trigonirostris,S. nanus,S. juncensis,S. willeti,S. sinuosus,S. veraepacis,S. palustris,S. bendiri,S. alaskanus, andS. pribilofensis.Figs. 11-14.Characters of the subgeneraSorexandOtisorex.Fig. 11.Medial view of right ramus ofSorex (Otisorex) vagrans. × 14.Fig. 12.Medial view of right ramus ofSorex (Sorex) arcticus. × 14.Fig. 13.Anterior view of left second upper unicuspid ofSorex (Otisorex)vagrans. × 45.Fig. 14.Anterior view of left second upper unicuspid ofSorex (Sorex)arcticus. × 45.Other species ofSorexnow occurring in North America differ fromOtisorexin having the 3rd unicuspid usually larger than 4th, in lacking a pigmented ridge from the apices to the cingula of the upper unicuspids, and in usually possessing a well-developed post-mandibular foramen. Exceptions to the last mentioned character areS. fumeusandS. dispar. The subgenusSorexin North America should include only the following species:S. jacksoni,S. tundrensis,S. arcticus,S. gaspensis,S. dispar,S. fumeus,S. trowbridgii,S. merriami, and all the members of the MexicanS. saussureigroup.The subgeneraOtisorexandSorexprobably separated in early Pleistocene or late Pliocene.Sorexis unknown in North America earlier than the late Pliocene (Simpson, 1945:51).In the genusMicrosorexthe characters of the subgenusOtisorexare carried to an extreme; the unicuspid ridges are prominent and end in distinct cusplets, and the 3rd unicuspid is not merely smaller than the 4th, but is reduced almost to the vanishing point. In addition, the post-mandibular foramen is absent. Although it is closer structurally toOtisorexthan toSorex, the recognition ofMicrosorexas a distinct genus seems warranted.Figure 15is intended to represent graphically some of the relationships discussed above. It must be re-emphasized that much of it is purely speculative, especially as regards actual time when various separations took place. It will be noted that I have indicated most separations as having taken place in interglacial ages. They are generally regarded as periods of warmth and aridity and, therefore, probably are times of segmentation of the ranges of boreal mammals and hence times exceptionally favorable to the process of speciation. Glacial ages, characterized by extensive and continuous areas of boreal habitat, probably were times of relatively unrestricted gene flow between many populations of boreal mammals and hence not favorable to rapid speciation.Sorex vagransWandering ShrewThe size of the wandering shrew varies from small in the subspeciesmonticolaandvagransto large in the subspeciespacificus. The tail makes up from a little more than a third to almost half of the total length. The color pattern ranges from tricolored through bicolored to almost monocolored. Color ranges from reddish (Sayal or Snuff Brown) to grayish in summer pelage and from black to light gray in winter. Diagnostic dental characters include: 3rd upper unicuspid smaller than 4th, and unicuspids, except 5th, with a pigmented ridge extending from near apex of each tooth medially to cingulum and sometimes ending as internal cusplet.S. vagransdiffers from membersof theornatusgroup in less flattened skull, and in more ventrally situated foramen magnum that encroaches more on the basioccipital and less on the supraoccipital. The wandering shrew differs fromS. trowbridgiiandS. saussureiin the dental characters mentioned above. These dental characters also serve to distinguishS. vagransreadily fromS. cinereus,S. merriami, andS. arcticuswhich may occur withvagrans. The large marsh shrew and water shrew,S. palustrisandS. bendiri, can be distinguished at a glance fromS. vagransby larger size and darker color.Fig. 15.Diagrammatic representation of the probable phylogeny ofSorex vagransand its near relatives.In the following treatment of the 29 subspecies ofSorex vagrans, the subspecies are arranged in geographic sequence, beginning with the southernmost large subspecies on the California coast and proceeding clockwise, north, east, south, and then west back to the starting point.Sorex vagrans sonomaeJacksonSorex pacificus sonomaeJackson, Jour. Mamm., 2:162, August 19, 1921.Type.—Adult female, skin and skull; No. 19658, Mus. Vert. Zool.; obtained on July 2, 1913, by Alfred C. Shelton, from Gualala, on the Sonoma County side of the Gualala River, Sonoma Co., California.Range.—Coastal California from Point Reyes north to Point Arena.Diagnosis.—Size large; average and extreme measurements of 3 topotypes are: total length, 141.7 (141-143); tail, 59 (54-63); hind foot, 17 (17-17). Color reddish in summer, somewhat grayer in winter.Fig. 16.Probable geographic ranges of 16 subspecies ofSorex vagrans.Guide to subspecies1.S. v. shumaginensis2.S. v. obscurus3.S. v. alascensis4.S. v. soperi5.S. v. isolatus6.S. v. setosus7.S. v. bairdi8.S. v. permiliensis9.S. v. yaquinae10.S. v. pacificus11.S. v. sonomae12.S. v. longiquus13.S. v. parvidens14.S. v. monticola15.S. v. neomexicanus16.S. v. orizabaeComparisons.—Differs fromS. v. pacificus, with which it intergrades to the north, in average smaller size and somewhat darker color; differs from the sympatricS. v. vagransin much larger size and more reddish color in both summer and winter.Remarks.—This subspecies inhabits the Transition Life-zone below 300 feet, and occurs on moist ground in forests and beneath dense vegetation.Marginal records.—California: Point Arena (Grinnell, 1933:82); Monte Rio (Jackson, 1928:144); Inverness (Grinnell, 1933:82).Sorex vagrans pacificusCouesSorex pacificusCoues, Bull. U. S. Geol. and Geog. Surv. Terr., 3 (3):650, May 15, 1877.Sorex pacificus pacificus, Jackson, Jour. Mamm., 2:162, August 19, 1921.Type.—Adult, sex unknown, skin and skull; No. 3266 U. S. Nat. Mus.; date of capture unknown; received from E. P. Vollum and catalogued on March 8, 1858; obtained at Ft. Umpqua, mouth of Umpqua River, Douglas Co., Oregon.Range.—Coast of California and Oregon from Mendocino north to Gardiner.Diagnosis.—Size large, largest of the species; average and extreme measurements of 8 specimens from Orick, Humboldt Co., California, are: total length, 143.1 (134-154); tail, 65.5 (59-72); hind foot, 17.5 (16-19). Color reddish in summer, browner or grayer in winter.Comparisons.—See account ofS. v. sonomaefor comparison with that subspecies; averaging larger in all dimensions thanS. v. yaquinaewith which it intergrades to the north; much larger and has more reddish than the sympatricS. v. vagrans.Remarks.—This subspecies occurs in the Canadian and Transition life-zones below 1500 ft. where there is found moist ground in or adjacent to heavy forests.Specimens examined.—Total number, 76.Oregon:Douglas Co.: Umpqua, 1 BS.Coos Co.: Marshfield, 1 BS; Myrtle Point, 1 BS.Josephine Co.: Bolan Lake, 1 SGJ.California:Del Norte Co.: Smith River, 2 BS; Gasquet, 4 BS; Crescent City, 17 BS.Humboldt Co.: Orick, 13 BS; 1 mi. N Trinidad, 18 FC; Trinidad Head, 1 BS; Carson's Camp, Mad River, Humboldt Bay, 5 BS; Arcata, 3 BS; Cape Mendocino, 2 BS; 5 mi. S Dyerville, 1 BS.Mendocino Co.: Mendocino, 6 BS.Marginal Records.—Oregon: Marshfield; Umpqua.California: Gasquet; 5 mi. S Dyerville; Mendocino, thence up coast to point of beginning.Sorex vagrans yaquinaeJacksonSorex yaquinaeJackson, Proc. Biol. Soc. Washington, 31:127, November 29, 1918.Sorex pacificus yaquinae, V. Bailey, N. Amer. Fauna, 55:364, August 29, 1936.Type.—Adult female, skin and skull; No. 73051 U. S. Biol. Surv. Coll., obtained on July 18, 1895, by B. J. Bretherton, from Yaquina Bay, Lincoln Co., Oregon.Diagnosis.—Size large for the species; average and extreme external measurementsof 11 specimens from Oakridge, Lane Co., Oregon, are: total length, 125.3 (11-136); tail, 55.1 (49-61); hind foot, 14.9 (14-16). Color reddish in summer, browner or grayer in winter.Comparisons.—See account ofS. v. pacificusfor comparison with that subspecies. Larger and more reddish thanS. v. bairdiwith which it intergrades to the north and east. Much larger and more reddish than the sympatricS. v. vagrans.Remarks.—The nameyaquinaeactually applies to a population of intergrades betweenpacificusandbairdi. There is much variation over the range of the subspecies, and individuals from the western and southern parts are larger than those from the west slope of the Cascades. Specimens from Vida and McKenzie Bridge are smaller than those from Mapleton, Mercer, and the type locality but still seem closer toyaquinaethan to topotypes ofbairdi. Between Marshfield and Umpqua on the one hand, and the Columbia River and the Cascade Mountains on the other, the size ofSorex vagransdecreases quite rapidly from the largepacificusto the smallerpermiliensis. Size decreases less rapidly northward along the coast than it does eastward toward the mountains; consequently, at any given latitude, coastal shrews are larger than mountain shrews. In this area of rapid change in size it is difficult to draw subspecific boundaries betweenpacificus,yaquinae, andbairdi, and this must be done somewhat arbitrarily.Jackson (1928:141) remarked upon the possibility that intergradation betweenpacificusandyaquinaetook place. He noted also the close resemblance betweenyaquinaeandbairdi, and stated (loc. cit.) that specific affinity between the two might be demonstrated with more specimens. He had a series of eight specimens from Vida, Oregon, seven of which he assigned toS. o. bairdiand one toyaquinae. I have examined these specimens and find no more variation between the largest and the smallest than would be expected in any normally variable series of shrews. Vernon Bailey (1936:364) arrangedyaquinaeas a subspecies ofpacificuswithout giving his reasons for so doing.Specimens examined.—Total number, 65.Oregon:Lincoln Co.: type locality, 2 AW.Benton Co.: Philomath, 2 BS.Lane Co.: Mable, 1 OU; Vida, 4 BS, 1 OSC, 3 OU; McKenzie Bridge, 8 OSC, 3 AW, 17 OU, 2 SGJ; Mercer, 1 OSC, 1 OU; Mapleton, 3 BS; Oakridge, 11 OU.Douglas Co.: Gardiner, 2 BS; Elkhead, 1 BS.Klamath Co.: Crescent Lake, 3 OU.Marginal Records.—Oregon: Yaquina Bay;Philomath; McKenzie Bridge; Prospect (Jackson, 1928:140); Crescent Lake; Gardiner.Sorex vagrans bairdiMerriamSorex bairdiMerriam, N. Amer. Fauna, 10:77, December 31, 1895.Sorex obscurus bairdi, Jackson, Proc. Biol. Soc. Washington, 31:127, November 29, 1918.Type.—Adult female, skin and skull; No. 17414/24318, U. S. Biol. Surv. Coll.; obtained on August 2, 1889, by T. S. Palmer, from Astoria, Clatsop Co., Oregon.Range.—Northwestern Oregon, south to Otis and east to Portland.Diagnosis.—Size medium for the species; average and extreme external measurements of 6 specimens from the type locality are: total length, 126.3 (124-130); tail, 55.0 (52-57); hind foot, 15.0 (14-15). Color Fuscous to Sepia in summer, darker in winter, underparts buffy.Comparisons.—For comparisons withyaquinaesee account of that subspecies. More reddish and larger thanpermiliensiswith whichbairdiintergrades to the east; specimens from Portland show evidence of such intergradation. Some specimens from southern Tillamook County show an approach toyaquinae.Remarks.—S. v. bairdilives primarily in forests as doyaquinaeandpacificus.Specimens examined.—Total number, 39.Oregon:Clatsop Co.: type locality, 12 BS; Seaside, 3 BS.Tillamook Co.: Netarts, 1 OU; Tillamook, 2 OSC; Blaine, 1 AW; Hebo Lake, 1 SGJ; 5 mi. SW Cloverdale, 1 AW.Multnomah Co.: Portland, 6 USNM.Lincoln Co.: Otis, 7 USNM; Delake, 1 KU.Lane Co.: north slope Three Sisters, 6000 ft., 4 BS.Marginal Records.—Oregon: type locality; Portland; north slope Three Sisters; Taft (Macnab and Dirks, 1941:178).Sorex vagrans permiliensisJacksonSorex obscurus permiliensisJackson, Proc. Biol. Soc. Washington, 31:128, November 29, 1918.Type.—Adult male, skin and skull; No. 91048, U. S. Biol. Surv. Coll.; obtained on October 2, 1897, by J. A. Loring from Permilia Lake, W base Mt. Jefferson, Cascade Range, Marion Co., Oregon.Range.—The Cascade Mountains of Oregon from Mt. Jefferson north to the Columbia River.Diagnosis.—Size medium for the species; average and extreme measurements of 14 specimens from the type locality are: total length, 117.7 (110-124); tail, 51.9 (45-58); hind foot, 14.0 (14-15). Pale reddish in summer, darker and brownish in winter.Comparisons.—For comparison withS. v. bairdisee account of that subspecies. Larger thanS. v. setosusexcept tail relatively shorter. More reddish in summer pelage thansetosus.Remarks.—S. v. bairdiis larger in the southern part of its range than elsewhere. Specimens from McKenzie Bridge, herein referred toyaquinae, are intermediate in character betweenyaquinaeandbairdior betweenyaquinaeandpermiliensis. The transition betweenyaquinaeandbairdiis much more gradual than betweenyaquinaeandpermiliensis.Specimens examined.—Total number, 21.Oregon:Hood River Co.: Mt. Hood, 2 BS.Wasco Co.: Camas Prairie, E base Cascade Mts., SE Mt. Hood, 1 BS.Marion Co.: Detroit, 1 BS; type locality, 17 BS.Marginal Records.—Oregon: Mt. Hood; type locality; Detroit.Sorex vagrans setosusElliottSorex setosusElliott, Field Columb. Mus. Publ. 32, zool. ser. 1:274, May 19, 1899.Sorex obscurus setosus, Jackson, Proc. Biol. Soc. Washington, 31:127, November 29, 1918.Type.—Adult male, skin and skull; No. 6213/238, Chicago Nat. Hist. Mus.; obtained on August 18, 1898, by D. G. Elliott from Happy Lake, Olympic Mts., Clallam Co., Washington.Range.—Washington from the Cascades west; southwestern British Columbia west of 120° W Longitude north to Lund.Diagnosis.—Size medium for the species; average and extreme measurements of 20 specimens from the Olympic Mountains, Washington, are: total length,117.3 (107-125); tail, 49.8 (41-54); hind foot, 13.4 (12-14). Color dark in both summer and winter.Comparisons.—For comparison withpermiliensissee account of that subspecies. Darker, longer-tailed, and somewhat larger cranially thanS. v. obscuruswith which it intergrades in southwestern British Columbia. Smaller in all dimensions, but much the same color asS. v. longicaudawith which it intergrades along the British Columbian coast north of Lund. Larger, darker, less reddish, and longer-tailed than the sympatricS. v. vagrans.Remarks.—S. v. setosuslives mostly in forests. According to Dalquest (1948:139) it is commonest at high altitudes in western Washington. In the Hudsonian Life-zone where shrew habitat is more restricted and marginal than it is at lower altitudes in the humid part of Washington,setosusmight be expected to compete withS. v. vagransand to supplant it. Records of occurrence in the Olympic Mountains suggest a degree of such separation there.Specimens examined.—Total number, 135.British Columbia: Lund, Malaspina Inlet, 4 BS; Gibson's Landing, 10 BS; Port Moody, 19 BS; Langley, 2 BS; Chilliwack, 1 BS; Manning Park, 2 PMBC.Washington:Whatcom Co.: Mt. Baker, 6 WSC; Barron, 1 BS.Chelan Co.: Clovay Pass, 1 WSC; Stehekin, 6 (4 WSC, 2 BS); Cascade Tunnel, 1 WSC.King Co.: Scenic, 1 WSC.Kittitas Co.: Lake Kachess, 1 WSC; Easton, 10 BS.Clallam Co.: 8 mi. W Sekin River, 1 WSC; mouth of Sekin River, 1 WSC; Clallam Bay, 1 CMNH; 7 mi. W Port Angeles, 1 WSC; Ozette Lake, 1 CMNH; 12 mi. S Port Angeles, 4 WSC; Forks, 1 CMNH; Deer Lake, 7 CMNH; Hoh Lake, 1 CMNH; Bogachiel Peak, 1 CMNH; Sol Duc Hot Springs, 3 CMNH; Sol Duc Park, 1 CMNH; Canyon Creek, 1 WSC; Sol Duc Divide, 2 WSC; Cat Creek, 2 WSC.Jefferson Co.: Jackson Ranger Station, 1 CMNH; Mt. Kimta, 2 CMNH; Reflection Lake, 6 CMNH; Blue Glacier, 3 CMNH.Gray's Harbor Co.: Westport, 1 WSC.Pierce Co.: Fort Lewis, 1 FC; Mt. Rainier, 19 (16 BS, 3 WSC).Pacific Co.: Tokeland, 2 BS.Yakima Co.: Gotchen Creek, 3 WSC; Mt. Adams, 1 WSC.Skamania Co.: Mt. St. Helens, 1.Oregon:Hood River Co.: 2 mi. W Parkdale, 2 BS.Marginal Records.—British Columbia: Rivers Inlet (Anderson, 1947:20);Agassiz(Jackson, 1928:136); Chilliwack Lake.Washington: Barron; Lyman Lake (Jackson, 1928:137); Mt. Stuart (Dalquest, 1948:141); Mt. Adams.Oregon:2 mi. W Parkdale.Washington: Ilwaco (Jackson, 1928:137); Lund, Malaspina Inlet.
Fig. 7.Possible distribution in Illinoian (inset) and Sangamonian times of the ancestor of theSorexvagrans-ornatus-longirostris-veraepaciscomplex. Approximate southern boundary of Illinoian glaciation marked by heavy line.
Fig. 7.Possible distribution in Illinoian (inset) and Sangamonian times of the ancestor of theSorexvagrans-ornatus-longirostris-veraepaciscomplex. Approximate southern boundary of Illinoian glaciation marked by heavy line.
In the ensuing Sangamonian interglacial age all glaciers retreated or disappeared thereby opening up extensive areas in the north and in the higher mountains which were occupied by a boreal fauna, includingS. vagrans. Concurrently the Great Basin, and probably also much of the Columbian Plateau, became dry, and desert conditions developed, perhaps much as they are today. Increasing aridity eliminated shrew habitat in most places between the Rocky Mountains and the Sierra Nevada-Cascade mountain chain with the result that the geographic range of the species resembled an inverted "U", one arm lying along the Rocky Mountains and the other along the Cascade-Sierra Nevada axis; the connection between the two arms was in British Columbia (seefig. 7). At presentSorex vagransdoes occur in isolated places in the Great Basin, but its existence there is tenuous and seemingly dependent upon the occurrence of permanent water such as Ruby Lake and Reese River. With such an arrangement as this it can readily be seen that gene flow between the eastern and western arms of the "U" would be greatly reduced by distance; consequently differentiation between the two might be expected.
Fig. 8.Possible distribution ofSorexvagransat two different times in the Wisconsinan Age. Left, early Wisconsinan; right, mid-Wisconsinan.
Fig. 8.Possible distribution ofSorexvagransat two different times in the Wisconsinan Age. Left, early Wisconsinan; right, mid-Wisconsinan.
Wisconsinan glaciation again rendered Canada uninhabitable, and it is quite possible that extensive areas in the Rocky Mountains, the Cascades and the Sierra Nevada were heavily glaciated. With the elimination of the northern part of the "U", the eastern andwestern arms became isolated, if not by the width of the Columbian Plateau at least by the glaciated Cascade Mountains. At the same time extensive areas on the Colorado Plateau and much of the area south to the Mexican highlands were again occupied by the species. Finally the Great Basin, again being well-watered, provided suitable habitat for, and was reoccupied by,Sorex vagrans(seefig. 8). This reoccupation of the Great Basin took place probably from the Colorado Plateau and mountains of Arizona and Utah, since the present day shrews of the speciesS. vagransin the Great Basin closely resemble Rocky Mountain shrews but differ markedly from the large endemic subspecies of the Pacific Coast.
Finally, with the waning of Wisconsinan ice, the species again was able to occupy northern and montane areas as it had during Sangamonian times. Again dessication of the Great Basin caused drastic restriction of shrew habitat. The small, marsh-dwelling kind of wandering shrew which had developed there around the lakes of Wisconsinan time occupied suitable habitat all the way to the Pacific coast where its range came into contact with that of the western arm of the Sangamonian "U."-pattern of shrew distribution (seefig. 9). The animals of this western segment and the new arrivals from the east were by this time so different from one another that the two kinds lived in the same areas without interbreeding. The descendants of the original western arm now are known asSorex vagrans sonomae,S. v. pacificus,S. v. yaquinae, andS. v. bairdi. The newcomers from the east are known asS. v. vagrans,S. v. halicoetes,S. v. paludivagusandS. v. vancouverensis.
In addition to occupying the Pacific Coast from San Francisco Bay north to the Fraser Delta, the Great Basin subspecies populated the Columbia Plateau and the western foothills of the central and northern Rockies. By so doing that subspecies came into secondary contact with its own parent stock with which it was still in reproductive continuity in Utah. In some places in British Columbia differentiation between the two kinds had proceeded to such an extent that some reproductive isolation was effected, but in many other places the two interbred. The Rocky Mountain form spread north and west and occupied the Cascades and coastal lowlands in southwestern British Columbia and in Washington. Here the differentiation between the Rocky Mountain subspecies and the Great Basin subspecies was great enough to cause complete reproductive isolation.
Fig. 9.Probable changes in the distribution ofSorex vagransconcurrent with and following the dissipation of Wisconsinan ice. Dark arrows in Washington, Idaho, Oregon, and California, showsS. v. vagrans.
Fig. 9.Probable changes in the distribution ofSorex vagransconcurrent with and following the dissipation of Wisconsinan ice. Dark arrows in Washington, Idaho, Oregon, and California, showsS. v. vagrans.
Deglaciation of the Sierra Nevada opened it up for reoccupation from the east bySorex vagranss of the Great Basin. In response to the montane environment the subspeciesobscuroides, resembling the subspeciesobscurusof the Rockies, developed.
Desiccation of the intermontane parts of New Mexico, Arizona, and Chihuahua, left "marooned" populations ofSorex vagranson suitable mountain ranges. In this waySorex vagrans orizabaemay have been isolated in southern Mexico. The isolated populations of Arizona and New Mexico differentiatedin situinto the subspeciesmonticolaandneomexicanus.
Western Canada and Alaska were populated by shrews which originated in the habitable parts of the Rocky Mountains and Colorado Plateau during Wisconsinan time (as opposed to shrews originating, as subspecies, in the Great Basin or on the Pacific Coast). These shrews differentiated into the currently recognized subspecies of the west coast and coastal islands of British Columbia and Alaska in response to the different environments in these places, many of which were isolated; the subspeciesisolatus,mixtus,setosus,longicauda,elassodon,prevostensis,malitiosus, andalaskensisare thought to have originated in this fashion after the areas now occupied by them were freed of Wisconsinan ice.
This group of shrews from the Rocky Mountains probably came into contact with the Pacific coastal segment of the species somewhere in northwestern Oregon. The clinal decrease in size fromS. v. pacificustoS. v. setosusseems steepest in this area. Upon the establishment of this contact reproductive continuity was resumed, probably because the temporal separation of the two stocks involved was not so great as, say, that betweenS. v. vagransandS. v. pacificus, and in addition the morphological differentiation was not so great.
On the eastern side of the Rockies the montane stock moved northeastward, occupying suitable territory opened up by the dissolution of the Laurentide ice sheet. Still later changes in the character of the northern plains owing to desiccation divided the range of the species and isolatedS. v. soperiin Manitoba and central Saskatchewan and a population ofS. v. obscurus, in the Cypress Hills. A number of semi-isolated stocks in central Montana became differentiated as a recognizable subspecies there.
A number of other boreal mammals have geographic ranges which resemble that ofSorex vagrans, except that the geographic ranges of subspecies do not overlap. Because of the general similaritiesof these geographic ranges, it is pertinent to examine the reasons suggested by students to account for the present geographic distributions of some of these other boreal species.
The red squirrel genus,Tamiasciurus, has a Rocky Mountain (and northern coniferous forest) species,T. hudsonicus, that occurs all along the Rocky Mountain chain and northward into Alaska. In the Cascade Mountains of Washington and British Columbia this species meets the range of a well marked western species,T. douglasii, with no evidence of intergradation. Dalquest (1948:86) attributes the divergence of the two species to separation in a glacial age but feels that the degree of difference between the two is too great to have all taken place during the Wisconsinan. Perhaps he has overemphasized the importance of the differences between the two, but, be that as it may, it seems that the two kinds differentiated during a glacial age when they were isolated, perhaps by ice on the Cascades into a coastal population and an inland population. One difference between the distribution of the red squirrels and vagrant shrew is that the squirrel of the Sierra Nevada is the species of the Pacific Coast, whereas the vagrant shrew of the Sierra Nevada was derived from the Great Basin population, which in turn was derived from the Rocky Mountain kind. Red squirrels do not occur on any of the boreal montane "islands" of Nevada. During the pluvial periods when hydrosere-loving shrews populated the Great Basin, that region may have been a treeless grassland. Vagrant shrews, then as now, probably depended on hydrosere communities, while red squirrels required trees. Therefore the shrews were able to traverse the Great Basin, while the Sierran red squirrels were of necessity derived from the coastal population.
The ecological requirements of jumping mice, genusZapus, and the subspecies ofSorex vagransthat dwell in hydroseres are essentially similar. The speciesZapus princepslives in the Rocky Mountains, the Great Basin, the Sierra Nevada, and north to Yukon (Krutzsch, 1954:395). Its geographic range is similar to that of the montane and basin segments ofS. vagrans. The speciesZ. trinotatusoccurs along the Pacific coast and in the Cascades north to southwestern British Columbia. Its distribution thus coincides in general with that of the large red coastal subspecies ofS. vagrans. Krutzsch (1954:368-369) thought that these two kinds of jumping mice were first separated by the formation of the Cascade Mountains and the Sierra Nevada and finally by Pleistocene glaciation. The Sierran jumping mouse (Zapus princeps), as is the Sierran vagrant shrew, is more closely related to the jumping mouse of theGreat Basin and of the Rocky Mountains than it is to the jumping mouse (Z. trinotatus) of the Pacific Coast, just as the Sierran vagrant shrew is related to the shrew of the Great Basin and Rocky Mountains. The jumping mouse also is limited in its distribution by hydrosere communities, not by forests.
In western North America there are two species of water or marsh shrews:Sorex palustrisandS. bendiri. They have been placed in separate subgenera, but, as pointed out beyond, are closely related and here are placed in the same subgenus. The speciespalustrisis found throughout the Rocky Mountains, north into Alaska, across the Great Basin into the Sierra Nevada, and west to the Pacific coast in Washington. The speciesbendiriis found from northwestern California north along the Pacific coast to southwestern British Columbia and east to the Cascades. Where the ranges of the two species overlap in western Washington they do not interbreed so far as is known, and are somewhat different in their ecology,bendiribeing a lowland, andpalustrisbeing a montane, species. The two species probably were separated in a glacial period as seems to have been the case with the wandering shrews. Also, the water shrew of the Sierra Nevada is derived from that of the Great Basin and Rocky Mountains.Sorex palustrisis tied closely in its distribution to hydrosere communities and is not dependent upon the presence of forests.
Red-backed mice, genusClethrionomys, occur throughout the Rocky Mountains and west to the Cascades in Washington as the speciesC. gapperi. The speciesC. californicusis found along the Pacific Coast from California north to the Olympic Peninsula. Where the ranges of the two species meet in Washington they seem not to intergrade. In some glacial interval these two species may have evolved in the same manner as has been described for the species ofZapusand those ofTamiasciurus. NoClethrionomysare found in the Sierra Nevada, nor are red-backed mice found in the boreal islands of the Great Basin. It is not known whyClethrionomys californicusdoes not occur in the Sierra Nevada. Some boreal birds have distributional patterns similar to those of the mammalian examples cited above. One kind of sapsucker,Sphyrapicus varius nuchalis, occurs in the Rocky Mountains north into British Columbia and west to the Cascades and Sierra Nevada. A related kind,S. varius ruber, occurs along the Pacific Coast from California north into British Columbia. Recently Howell (1952) has shown that some intergradation takes place betweenruberandnuchalisin Washington and British Columbia, although they do not intergradefreely. Previously the two kinds were thought not to intergrade and were regarded as two species. The two kinds intergrade also in northeastern California, although in that stateS. v. daggeti, rather thanS. v. ruber, is involved in the intergradation. Howell considered the two kinds to be conspecific with one another as well as with the easternS. varius. He attributed a measure of the distinctness ofnuchalisandruberto their separation during a glacial period, but felt that the separation was much older than Wisconsinan. Whatever the time of separation, the pattern seems clear:nuchalisandruber(as well asvarius) were separated into montane, coastal, and eastern segments respectively, probably by glaciation (it seems to me in the Pleistocene), and have since re-established contact with one another.
The grouse genusDendrogapusis divided into a Great Basin species,D. obscurus, which extends northward into British Columbia, and a Rocky Mountain species,D. fuliginosus, that is found in the Sierra Nevada and northward along the coast and Cascades into British Columbia. Although the two kinds have at times been considered conspecific, they differ in voice, hooting mechanism, and characters of the downy young, and so far no actual intergradation between the two has been shown (Grinnell and Miller, 1944:113). These grouse thus seem to offer additional evidence for a Pleistocene, possibly Wisconsinan, separation of the boreal fauna into a Rocky Mountain and a Pacific coastal segment.
A notable sidelight on these data is the frequency with which species in the Sierra Nevada have their closest relatives in the Rocky Mountains, rather than in the geographically nearer Cascades or coastal areas. This similarity in fauna of the Sierra Nevada and the Rockies was noted long ago by Merriam (1899:86).
RELATIONSHIPS WITH OTHER SPECIES
During the Sangamonian interval, isolated segments of the once widespread ancestralSorex vagransquite possibly persisted in such places as the Sierra Nevada, coastal southern California, the mountains of Arizona, New Mexico, and southern Mexico, and in the Black Hills (seefig. 6). One might expect that by Wisconsinan time these populations would have become reproductively isolated from their parent stock. They would therefore have remained specifically distinct when WisconsinanSorex vagrans, reoccupied these outlying areas, and may still be found isolated in places peripheral to the range of the ancestral species.
Fig. 10.Probable distribution ofS.veraepacis,S. longirostris, and theS. ornatusgroup (stipple) and of their Wisconsinan ancestors (lines). Heavy line indicates limits of Wisconsinan glaciation.
Fig. 10.Probable distribution ofS.veraepacis,S. longirostris, and theS. ornatusgroup (stipple) and of their Wisconsinan ancestors (lines). Heavy line indicates limits of Wisconsinan glaciation.
In fact, we do find species closely related toSorex vagransin just such places today (fig. 10). ProbablySorex ornatus, including members of theornatusgroup such asS. trigonirostris,S. sinuosus,S. willeti,S. tenellus, andS. nanus, and alsoS. veraepacis, arose by separation from the ancestralvagransstock in Sangamonian time. Probably the easternS. longirostrisarose in a like manner. The ancestor ofS. ornatusmay have been isolated in southwestern California during Sangamonian time, spread north and south during the Wisconsinan age, and afterward given rise toS. trigonirostrisand the modernS. ornatuscomplex of California and Baja California. In at least one place reproductive isolation betweenornatusand the invadingS. vagranshas broken down (Rudd, 1953); the place is a salt marsh along San Pablo Bay, where a hybrid population betweenS. vagransandS. sinuosus, anornatusderivative, has formed.Sorex tenellusmay have been isolated in the Sierra Nevada in the Sangamonianinterval, moved into the valleys east of the mountains during the Wisconsinan age, and become restricted to its present range since the retreat of the last ice.Sorex nanusmay have occurred in the Black Hills and isolated mountains of Arizona and New Mexico during the Sangamonian interval and remained in these general areas during the Wisconsinan age. Its present range is peripheral to the main body of the Rockies and the Colorado Plateau.
The eastern speciesSorex longirostrishas many similarities with shrews of theornatus-vagransstock.S. l. longirostrisis close in many ways toS. nanus. Indeed, the differences between the speciesS. nanus,S. ornatus, andS. longirostrisseem to me to be of the same magnitude and indicate a similar period of differentiation from a common ancestor. The ancestor ofS. longirostrismay have gained access to the eastern United States in the Illinoian Ageviathe northern Great Plains south of the glacial boundary (fig. 7). The ancestor ofSorex veraepacisof southern Mexico probably reached that area in Illinoian time as part of the ancestralvagransstock and probably attained its differentiation during the Sangamonian interval.
All the kinds of shrews so far discussed, including theS. vagranscomplex, might thus be thought of as having had a common ancestor in the Illinoian Age. This entire group of shrews has the third unicuspid smaller than the fourth, a pigmented ridge from the apex to the cingulum of each upper unicuspid, and, in most individuals, lacks a post-mandibular foramen in the lower jaw (Findley, 1953:636-637). The pigment is not always prominent inS. longirostris.
Two other species of North American shrews,Sorex palustris, the water shrew, andSorex bendiri, the marsh shrew, show these three characters to a greater or lesser degree, and it seems that these two species and thevagrans-ornatus-veraepacisgroup had a common ancestor, probably before Illinoian time for reasons stated beyond. I judge, however, that far from being subgenerically distinct as they have been considered to be,S. palustrisandS. bendiriare actually closely related species of the same subgenus and may have differentiated from one another because of separation into eastern (palustris) and western (bendiri) segments in the Sangamonian interval, much as has been postulated concerning the eastern and western stocks ofSorex vagrans. Indeed, Jackson (1928:192) has noted that in the Pacific northwest the characters of the two kinds approach one another and become differences of degree only.
The widespread speciesSorex cinereusresembles all the foregoing species in the ridges on the unicuspid teeth and in the lack of a post-mandibular foramen, but differs from those other species inhaving the third upper unicuspid larger than the fourth. The subspeciesS. cinereus ohionensis, however, often has the sizes of these teeth reversed. WithS. cinereusI includeS. preblei(eastern Oregon) andS. lyelli(Sierra Nevada), both obviously closely related tocinereusas Jackson (1928:37) recognized when he included them in thecinereusgroup.Sorex milleri(Coahuila and central western Nuevo Leon) seems to me to resembleS. cinereusmore than it does other species of North AmericanSorex, and I judge that it also belongs to thecinereusgroup.Sorex cinereusand its close relatives seem more closely related to the species which have thus far been discussed than they do to such other North American species asS. arcticus,S. fumeus,S. trowbridgii,S. merriami, and the members of theS. saussureigroup; most of these five species last mentioned possess a post-mandibular foramen, lack pigmented unicuspid ridges, and have the third unicuspid larger than the fourth. Because of the morphological resemblances mentioned above, it seems likely to me thatS. cinereusand thevagrans-ornatus-veraepacis-palustriscomplex had a common ancestor in early Pleistocene time.Sorex cinereushas recently been considered to be conspecific with the Old WorldS. caecutiensLaxmann (Van den Brink, 1953) which name, being the older, would apply to the circumpolar species.
Hibbard (1944:719) recoveredS. cinereusand a species ofNeosorex(a name formerly applied to the water shrew) from the Pleistocene (late Kansan) Cudahy Fauna. This indicates that the ancestors of the modernS. cinereusand of the water shrew had diverged from one another before that time. Brown (1908:172) recordedS. cinereusandS. obscurusfrom the Conard Fissure in Arkansas. These materials were deposited probably at a later time than was the Cudahy Fauna. TheS. obscurusfrom Conard Fissure probably represents the ancestralS. vagransstock which I think reached eastern United States in Illinoian time and gave rise toS. longirostris. The Conard Fissure material was deposited at a time (Illinoian?) when northern faunas extended farther south than they do today.
All of the species mentioned as having structural characters in common withS. vagransseem to have arisen from a common ancestor which had already differentiated from the ancestor of such species asS. arcticus,S. saussurei, and others. Consequently all are here included in a single subgenus. The oldest generic name applied to a shrew of this group, other than the nameSorex, isOtisorexDeKay, 1842, type speciesOtisorex platyrhinusDeKay, asynonym ofSorex cinereus. The subgenus can be characterized as follows.
SubgenusOtisorexDeKay
1842.OtisorexDeKay, Zoology of New York, pt. 1, Mammalia, p. 22, and pl. 5, fig. 1. Type,Otisorex platyrhinusDeKay (=Sorex cinereusKerr).
Third unicuspid usually smaller than fourth; upper unicuspids usually with pigmented ridge extending from apices medially to cingula, uninterrupted by antero-posterior groove; post-mandibular foramen usually absent. Includes the speciesS. cinereus,S. longirostris,S. vagrans,S. ornatus,S. tenellus,S. trigonirostris,S. nanus,S. juncensis,S. willeti,S. sinuosus,S. veraepacis,S. palustris,S. bendiri,S. alaskanus, andS. pribilofensis.
Figs. 11-14.Characters of the subgeneraSorexandOtisorex.Fig. 11.Medial view of right ramus ofSorex (Otisorex) vagrans. × 14.Fig. 12.Medial view of right ramus ofSorex (Sorex) arcticus. × 14.Fig. 13.Anterior view of left second upper unicuspid ofSorex (Otisorex)vagrans. × 45.Fig. 14.Anterior view of left second upper unicuspid ofSorex (Sorex)arcticus. × 45.
Figs. 11-14.Characters of the subgeneraSorexandOtisorex.Fig. 11.Medial view of right ramus ofSorex (Otisorex) vagrans. × 14.Fig. 12.Medial view of right ramus ofSorex (Sorex) arcticus. × 14.Fig. 13.Anterior view of left second upper unicuspid ofSorex (Otisorex)vagrans. × 45.Fig. 14.Anterior view of left second upper unicuspid ofSorex (Sorex)arcticus. × 45.
Other species ofSorexnow occurring in North America differ fromOtisorexin having the 3rd unicuspid usually larger than 4th, in lacking a pigmented ridge from the apices to the cingula of the upper unicuspids, and in usually possessing a well-developed post-mandibular foramen. Exceptions to the last mentioned character areS. fumeusandS. dispar. The subgenusSorexin North America should include only the following species:S. jacksoni,S. tundrensis,S. arcticus,S. gaspensis,S. dispar,S. fumeus,S. trowbridgii,S. merriami, and all the members of the MexicanS. saussureigroup.
The subgeneraOtisorexandSorexprobably separated in early Pleistocene or late Pliocene.Sorexis unknown in North America earlier than the late Pliocene (Simpson, 1945:51).
In the genusMicrosorexthe characters of the subgenusOtisorexare carried to an extreme; the unicuspid ridges are prominent and end in distinct cusplets, and the 3rd unicuspid is not merely smaller than the 4th, but is reduced almost to the vanishing point. In addition, the post-mandibular foramen is absent. Although it is closer structurally toOtisorexthan toSorex, the recognition ofMicrosorexas a distinct genus seems warranted.
Figure 15is intended to represent graphically some of the relationships discussed above. It must be re-emphasized that much of it is purely speculative, especially as regards actual time when various separations took place. It will be noted that I have indicated most separations as having taken place in interglacial ages. They are generally regarded as periods of warmth and aridity and, therefore, probably are times of segmentation of the ranges of boreal mammals and hence times exceptionally favorable to the process of speciation. Glacial ages, characterized by extensive and continuous areas of boreal habitat, probably were times of relatively unrestricted gene flow between many populations of boreal mammals and hence not favorable to rapid speciation.
Sorex vagrans
Wandering Shrew
The size of the wandering shrew varies from small in the subspeciesmonticolaandvagransto large in the subspeciespacificus. The tail makes up from a little more than a third to almost half of the total length. The color pattern ranges from tricolored through bicolored to almost monocolored. Color ranges from reddish (Sayal or Snuff Brown) to grayish in summer pelage and from black to light gray in winter. Diagnostic dental characters include: 3rd upper unicuspid smaller than 4th, and unicuspids, except 5th, with a pigmented ridge extending from near apex of each tooth medially to cingulum and sometimes ending as internal cusplet.S. vagransdiffers from membersof theornatusgroup in less flattened skull, and in more ventrally situated foramen magnum that encroaches more on the basioccipital and less on the supraoccipital. The wandering shrew differs fromS. trowbridgiiandS. saussureiin the dental characters mentioned above. These dental characters also serve to distinguishS. vagransreadily fromS. cinereus,S. merriami, andS. arcticuswhich may occur withvagrans. The large marsh shrew and water shrew,S. palustrisandS. bendiri, can be distinguished at a glance fromS. vagransby larger size and darker color.
Fig. 15.Diagrammatic representation of the probable phylogeny ofSorex vagransand its near relatives.
Fig. 15.Diagrammatic representation of the probable phylogeny ofSorex vagransand its near relatives.
In the following treatment of the 29 subspecies ofSorex vagrans, the subspecies are arranged in geographic sequence, beginning with the southernmost large subspecies on the California coast and proceeding clockwise, north, east, south, and then west back to the starting point.
Sorex vagrans sonomaeJackson
Sorex pacificus sonomaeJackson, Jour. Mamm., 2:162, August 19, 1921.
Type.—Adult female, skin and skull; No. 19658, Mus. Vert. Zool.; obtained on July 2, 1913, by Alfred C. Shelton, from Gualala, on the Sonoma County side of the Gualala River, Sonoma Co., California.
Range.—Coastal California from Point Reyes north to Point Arena.
Diagnosis.—Size large; average and extreme measurements of 3 topotypes are: total length, 141.7 (141-143); tail, 59 (54-63); hind foot, 17 (17-17). Color reddish in summer, somewhat grayer in winter.
Fig. 16.Probable geographic ranges of 16 subspecies ofSorex vagrans.Guide to subspecies1.S. v. shumaginensis2.S. v. obscurus3.S. v. alascensis4.S. v. soperi5.S. v. isolatus6.S. v. setosus7.S. v. bairdi8.S. v. permiliensis9.S. v. yaquinae10.S. v. pacificus11.S. v. sonomae12.S. v. longiquus13.S. v. parvidens14.S. v. monticola15.S. v. neomexicanus16.S. v. orizabae
Fig. 16.Probable geographic ranges of 16 subspecies ofSorex vagrans.Guide to subspecies1.S. v. shumaginensis2.S. v. obscurus3.S. v. alascensis4.S. v. soperi5.S. v. isolatus6.S. v. setosus7.S. v. bairdi8.S. v. permiliensis9.S. v. yaquinae10.S. v. pacificus11.S. v. sonomae12.S. v. longiquus13.S. v. parvidens14.S. v. monticola15.S. v. neomexicanus16.S. v. orizabae
Comparisons.—Differs fromS. v. pacificus, with which it intergrades to the north, in average smaller size and somewhat darker color; differs from the sympatricS. v. vagransin much larger size and more reddish color in both summer and winter.
Remarks.—This subspecies inhabits the Transition Life-zone below 300 feet, and occurs on moist ground in forests and beneath dense vegetation.
Marginal records.—California: Point Arena (Grinnell, 1933:82); Monte Rio (Jackson, 1928:144); Inverness (Grinnell, 1933:82).
Sorex vagrans pacificusCoues
Sorex pacificusCoues, Bull. U. S. Geol. and Geog. Surv. Terr., 3 (3):650, May 15, 1877.
Sorex pacificus pacificus, Jackson, Jour. Mamm., 2:162, August 19, 1921.
Type.—Adult, sex unknown, skin and skull; No. 3266 U. S. Nat. Mus.; date of capture unknown; received from E. P. Vollum and catalogued on March 8, 1858; obtained at Ft. Umpqua, mouth of Umpqua River, Douglas Co., Oregon.
Range.—Coast of California and Oregon from Mendocino north to Gardiner.
Diagnosis.—Size large, largest of the species; average and extreme measurements of 8 specimens from Orick, Humboldt Co., California, are: total length, 143.1 (134-154); tail, 65.5 (59-72); hind foot, 17.5 (16-19). Color reddish in summer, browner or grayer in winter.
Comparisons.—See account ofS. v. sonomaefor comparison with that subspecies; averaging larger in all dimensions thanS. v. yaquinaewith which it intergrades to the north; much larger and has more reddish than the sympatricS. v. vagrans.
Remarks.—This subspecies occurs in the Canadian and Transition life-zones below 1500 ft. where there is found moist ground in or adjacent to heavy forests.
Specimens examined.—Total number, 76.
Oregon:Douglas Co.: Umpqua, 1 BS.Coos Co.: Marshfield, 1 BS; Myrtle Point, 1 BS.Josephine Co.: Bolan Lake, 1 SGJ.
California:Del Norte Co.: Smith River, 2 BS; Gasquet, 4 BS; Crescent City, 17 BS.Humboldt Co.: Orick, 13 BS; 1 mi. N Trinidad, 18 FC; Trinidad Head, 1 BS; Carson's Camp, Mad River, Humboldt Bay, 5 BS; Arcata, 3 BS; Cape Mendocino, 2 BS; 5 mi. S Dyerville, 1 BS.Mendocino Co.: Mendocino, 6 BS.
Marginal Records.—Oregon: Marshfield; Umpqua.California: Gasquet; 5 mi. S Dyerville; Mendocino, thence up coast to point of beginning.
Sorex vagrans yaquinaeJackson
Sorex yaquinaeJackson, Proc. Biol. Soc. Washington, 31:127, November 29, 1918.
Sorex pacificus yaquinae, V. Bailey, N. Amer. Fauna, 55:364, August 29, 1936.
Type.—Adult female, skin and skull; No. 73051 U. S. Biol. Surv. Coll., obtained on July 18, 1895, by B. J. Bretherton, from Yaquina Bay, Lincoln Co., Oregon.
Diagnosis.—Size large for the species; average and extreme external measurementsof 11 specimens from Oakridge, Lane Co., Oregon, are: total length, 125.3 (11-136); tail, 55.1 (49-61); hind foot, 14.9 (14-16). Color reddish in summer, browner or grayer in winter.
Comparisons.—See account ofS. v. pacificusfor comparison with that subspecies. Larger and more reddish thanS. v. bairdiwith which it intergrades to the north and east. Much larger and more reddish than the sympatricS. v. vagrans.
Remarks.—The nameyaquinaeactually applies to a population of intergrades betweenpacificusandbairdi. There is much variation over the range of the subspecies, and individuals from the western and southern parts are larger than those from the west slope of the Cascades. Specimens from Vida and McKenzie Bridge are smaller than those from Mapleton, Mercer, and the type locality but still seem closer toyaquinaethan to topotypes ofbairdi. Between Marshfield and Umpqua on the one hand, and the Columbia River and the Cascade Mountains on the other, the size ofSorex vagransdecreases quite rapidly from the largepacificusto the smallerpermiliensis. Size decreases less rapidly northward along the coast than it does eastward toward the mountains; consequently, at any given latitude, coastal shrews are larger than mountain shrews. In this area of rapid change in size it is difficult to draw subspecific boundaries betweenpacificus,yaquinae, andbairdi, and this must be done somewhat arbitrarily.
Jackson (1928:141) remarked upon the possibility that intergradation betweenpacificusandyaquinaetook place. He noted also the close resemblance betweenyaquinaeandbairdi, and stated (loc. cit.) that specific affinity between the two might be demonstrated with more specimens. He had a series of eight specimens from Vida, Oregon, seven of which he assigned toS. o. bairdiand one toyaquinae. I have examined these specimens and find no more variation between the largest and the smallest than would be expected in any normally variable series of shrews. Vernon Bailey (1936:364) arrangedyaquinaeas a subspecies ofpacificuswithout giving his reasons for so doing.
Specimens examined.—Total number, 65.Oregon:Lincoln Co.: type locality, 2 AW.Benton Co.: Philomath, 2 BS.Lane Co.: Mable, 1 OU; Vida, 4 BS, 1 OSC, 3 OU; McKenzie Bridge, 8 OSC, 3 AW, 17 OU, 2 SGJ; Mercer, 1 OSC, 1 OU; Mapleton, 3 BS; Oakridge, 11 OU.Douglas Co.: Gardiner, 2 BS; Elkhead, 1 BS.Klamath Co.: Crescent Lake, 3 OU.
Marginal Records.—Oregon: Yaquina Bay;Philomath; McKenzie Bridge; Prospect (Jackson, 1928:140); Crescent Lake; Gardiner.
Sorex vagrans bairdiMerriam
Sorex bairdiMerriam, N. Amer. Fauna, 10:77, December 31, 1895.
Sorex obscurus bairdi, Jackson, Proc. Biol. Soc. Washington, 31:127, November 29, 1918.
Type.—Adult female, skin and skull; No. 17414/24318, U. S. Biol. Surv. Coll.; obtained on August 2, 1889, by T. S. Palmer, from Astoria, Clatsop Co., Oregon.
Range.—Northwestern Oregon, south to Otis and east to Portland.
Diagnosis.—Size medium for the species; average and extreme external measurements of 6 specimens from the type locality are: total length, 126.3 (124-130); tail, 55.0 (52-57); hind foot, 15.0 (14-15). Color Fuscous to Sepia in summer, darker in winter, underparts buffy.
Comparisons.—For comparisons withyaquinaesee account of that subspecies. More reddish and larger thanpermiliensiswith whichbairdiintergrades to the east; specimens from Portland show evidence of such intergradation. Some specimens from southern Tillamook County show an approach toyaquinae.
Remarks.—S. v. bairdilives primarily in forests as doyaquinaeandpacificus.
Specimens examined.—Total number, 39.Oregon:Clatsop Co.: type locality, 12 BS; Seaside, 3 BS.Tillamook Co.: Netarts, 1 OU; Tillamook, 2 OSC; Blaine, 1 AW; Hebo Lake, 1 SGJ; 5 mi. SW Cloverdale, 1 AW.Multnomah Co.: Portland, 6 USNM.Lincoln Co.: Otis, 7 USNM; Delake, 1 KU.Lane Co.: north slope Three Sisters, 6000 ft., 4 BS.
Marginal Records.—Oregon: type locality; Portland; north slope Three Sisters; Taft (Macnab and Dirks, 1941:178).
Sorex vagrans permiliensisJackson
Sorex obscurus permiliensisJackson, Proc. Biol. Soc. Washington, 31:128, November 29, 1918.
Type.—Adult male, skin and skull; No. 91048, U. S. Biol. Surv. Coll.; obtained on October 2, 1897, by J. A. Loring from Permilia Lake, W base Mt. Jefferson, Cascade Range, Marion Co., Oregon.
Range.—The Cascade Mountains of Oregon from Mt. Jefferson north to the Columbia River.
Diagnosis.—Size medium for the species; average and extreme measurements of 14 specimens from the type locality are: total length, 117.7 (110-124); tail, 51.9 (45-58); hind foot, 14.0 (14-15). Pale reddish in summer, darker and brownish in winter.
Comparisons.—For comparison withS. v. bairdisee account of that subspecies. Larger thanS. v. setosusexcept tail relatively shorter. More reddish in summer pelage thansetosus.
Remarks.—S. v. bairdiis larger in the southern part of its range than elsewhere. Specimens from McKenzie Bridge, herein referred toyaquinae, are intermediate in character betweenyaquinaeandbairdior betweenyaquinaeandpermiliensis. The transition betweenyaquinaeandbairdiis much more gradual than betweenyaquinaeandpermiliensis.
Specimens examined.—Total number, 21.Oregon:Hood River Co.: Mt. Hood, 2 BS.Wasco Co.: Camas Prairie, E base Cascade Mts., SE Mt. Hood, 1 BS.Marion Co.: Detroit, 1 BS; type locality, 17 BS.
Marginal Records.—Oregon: Mt. Hood; type locality; Detroit.
Sorex vagrans setosusElliott
Sorex setosusElliott, Field Columb. Mus. Publ. 32, zool. ser. 1:274, May 19, 1899.
Sorex obscurus setosus, Jackson, Proc. Biol. Soc. Washington, 31:127, November 29, 1918.
Type.—Adult male, skin and skull; No. 6213/238, Chicago Nat. Hist. Mus.; obtained on August 18, 1898, by D. G. Elliott from Happy Lake, Olympic Mts., Clallam Co., Washington.
Range.—Washington from the Cascades west; southwestern British Columbia west of 120° W Longitude north to Lund.
Diagnosis.—Size medium for the species; average and extreme measurements of 20 specimens from the Olympic Mountains, Washington, are: total length,117.3 (107-125); tail, 49.8 (41-54); hind foot, 13.4 (12-14). Color dark in both summer and winter.
Comparisons.—For comparison withpermiliensissee account of that subspecies. Darker, longer-tailed, and somewhat larger cranially thanS. v. obscuruswith which it intergrades in southwestern British Columbia. Smaller in all dimensions, but much the same color asS. v. longicaudawith which it intergrades along the British Columbian coast north of Lund. Larger, darker, less reddish, and longer-tailed than the sympatricS. v. vagrans.
Remarks.—S. v. setosuslives mostly in forests. According to Dalquest (1948:139) it is commonest at high altitudes in western Washington. In the Hudsonian Life-zone where shrew habitat is more restricted and marginal than it is at lower altitudes in the humid part of Washington,setosusmight be expected to compete withS. v. vagransand to supplant it. Records of occurrence in the Olympic Mountains suggest a degree of such separation there.
Specimens examined.—Total number, 135.
British Columbia: Lund, Malaspina Inlet, 4 BS; Gibson's Landing, 10 BS; Port Moody, 19 BS; Langley, 2 BS; Chilliwack, 1 BS; Manning Park, 2 PMBC.
Washington:Whatcom Co.: Mt. Baker, 6 WSC; Barron, 1 BS.Chelan Co.: Clovay Pass, 1 WSC; Stehekin, 6 (4 WSC, 2 BS); Cascade Tunnel, 1 WSC.King Co.: Scenic, 1 WSC.Kittitas Co.: Lake Kachess, 1 WSC; Easton, 10 BS.Clallam Co.: 8 mi. W Sekin River, 1 WSC; mouth of Sekin River, 1 WSC; Clallam Bay, 1 CMNH; 7 mi. W Port Angeles, 1 WSC; Ozette Lake, 1 CMNH; 12 mi. S Port Angeles, 4 WSC; Forks, 1 CMNH; Deer Lake, 7 CMNH; Hoh Lake, 1 CMNH; Bogachiel Peak, 1 CMNH; Sol Duc Hot Springs, 3 CMNH; Sol Duc Park, 1 CMNH; Canyon Creek, 1 WSC; Sol Duc Divide, 2 WSC; Cat Creek, 2 WSC.Jefferson Co.: Jackson Ranger Station, 1 CMNH; Mt. Kimta, 2 CMNH; Reflection Lake, 6 CMNH; Blue Glacier, 3 CMNH.Gray's Harbor Co.: Westport, 1 WSC.Pierce Co.: Fort Lewis, 1 FC; Mt. Rainier, 19 (16 BS, 3 WSC).Pacific Co.: Tokeland, 2 BS.Yakima Co.: Gotchen Creek, 3 WSC; Mt. Adams, 1 WSC.Skamania Co.: Mt. St. Helens, 1.
Oregon:Hood River Co.: 2 mi. W Parkdale, 2 BS.
Marginal Records.—British Columbia: Rivers Inlet (Anderson, 1947:20);Agassiz(Jackson, 1928:136); Chilliwack Lake.Washington: Barron; Lyman Lake (Jackson, 1928:137); Mt. Stuart (Dalquest, 1948:141); Mt. Adams.Oregon:2 mi. W Parkdale.Washington: Ilwaco (Jackson, 1928:137); Lund, Malaspina Inlet.