Part 21

On July 1, 1917, in Clay County, Nebraska, a nest with four young was found (Swenk, 1926:321). On July 29, 1939, an adult and five young were plowed out of the ground in Allegan County, Michigan; one of the two young males weighed 40.5 grams two days after capture (Allen, 1940:459-460). On August 12, 1932, ten young with the mother, were found in Roseau County, Minnesota (Swanson and Fryklund, 1935:125). September appears to have been the month of birth of a specimen, no. 8472 in the Carnegie Museum, taken on November 24 in Pittsburgh, Pennsylvania. In October, a young least weasel is recorded from Pennsylvania (Winecoff, 1930:313). Early December was the time of birth of a specimen, approximately 10 weeks old, no. 88077, University of Michigan, taken on February 21 in Allegan County. On December 25, 1927, in Washington County, Pennsylvania, "five full-sized, though young . . . animals were caught under the same pile of corn fodder" (Sutton, 1929:253). The first week of January seems to have been the time of birth of a juvenile, no. 88080, University of Michigan, taken in Livingston County, Michigan, on March 27, 1943, since the specimen is approximately seven weeks old. On January 15, 1929, in Washington County, Pennsylvania, four young with the eyes yet unopened were obtained from a nest (Sutton, 1929:254). On January 25, 1928, young, the eyes of which may not yet have been open, were taken from a den in Washington County, Pennsylvania, by Winecoff (1930:313), who records other young having been taken in the same month as well as in February. On March 10, a female from North Portal, Saskatchewan, gave birth to four young (Dunk, 1946:392). On April 18, 1916, four young, half grown, were taken in Nebraska (Swenk, 1926:317). On April 2, 1929, three young were found in Roseau County, Minnesota, according to Swanson and Fryklund (1935:125) who remark that: "The Pennsylvania and Minnesota records show that least weasels may be born any time from July to early February in the northern states." Now, with all of the above records available, it turns out that November, May and June are the only months in which young least weasels have not been reported. Of course some of the young, for which the ages were not specified, were born in preceding months. Even so, the data now available suggests that, in the United States, young least weasels may be born in every month of the year. The number per litter is 3, 4, 4, 4, 5, 5, and 10, yielding an average of 5.

The rate of growth of the young has not been studied enough to allow of judging if it differs significantly from that of other species of the genus. Allen (1940:459-460), however, tells us that of the three young females and two young males captured on July 29, 1939, in Allegan County, Michigan, one male that was killed on July 31, 1939, weighed 40.5 grams. The male remaining alive increased from 46 grams (August 5) to 62.5 grams on September 20, having eaten 63 mice while in captivity. The females in the period of August 5 to September 4 increased in weight as follows: 41 up to 49 grams; 44 to 50 grams; and 47 to 58 grams, having eaten, by September 26, 60, 64 and 65 mice.

Concerning a nest in which young were found, Sutton (1929:254) writes that on January 15, 1929, near Burgettstown, Washington County, Pennsylvania, an animal was seen to enter a small hole in a creek bank. After the observer dug in a distance of approximately six inches an adult, female least weasel was seen and obtained. Back of the animal, the hole, which turned sharply downward, was full of water. The weasel first seen was a female nursing young. A chamber, to the side of the hole, filled with dead grass, comprised a nest containing four young with the eyes yet unopened. Several nests occupied by adult least weasels or by least weasels that were old enough to shift for themselves have been found. Polderboer (1942:145-147) in the winter of 1939-40, on a 144 acre farm in Butler County, Iowa, found four least weasels living, singly, in burrows dug by moles and pocket gophers. The nests therein made by mice were used by the least weasels. Winecoff (1930:312-313) mentions one den in Pennsylvania that contained the remains of only mice, "and not a hint of a feather." Above, in the account of food of the least weasel, Criddle's (1926:199-200) account of the havoc wrought by least weasels among the meadow mice (_Microtus ochrogaster minor_) has been given. In this account he mentions the fur-lined nests of the weasels that had appropriated the homes of the _Microtus_. Criddle's (1947:69) later account of a nest at Treesbank, Manitoba, is as follows: "A Nest of the Least Weasel.--When a least weasel finds its way into a locality that has a large number of mice in it, it selects for its home one of their nests that has been made in a well concealed place. This it immediately starts to improve by lining it with hair plucked from its victims before eating them; and as long as sufficient numbers of mice remain in the district the weasel continues adding their hair to the nest, so that the thickness of its walls give one a good idea of the length of time it has been in use. The nest is not only used for sleeping in, as most of the food is consumed in it. Frozen mice are taken in to be thawed out and the weasel carries those it has recently killed in to prevent them getting frozen, or perhaps to have them warm for its next meal.

"On January 27, 1946, my son Percy called my attention to a nest that he had just uncovered in a clover stack that we were using. This nest had originally been made by a Drummond's vole, _Microtus pennsylvanicus drummondii_, and taken from it by the least weasel, _Mustela rixosa_, the tracks of which had been noticed about the stack yard since the first snow in early November.

"The nest had evidently been in use for at least three months and the continual additions made to its walls had been so great that they were nearly an inch thick of hair matted together so closely that it appeared to be felt. The hair alone weighed nearly 22 gm., so that with this for protection the weasel must have been warm and comfortable through the severest winter weather.

"In the nest were two red-backed mice, _Clethrionomys gapperi_, one of which had the base of its skull eaten out. No hair had been removed from either of them, but a _Microtus_ lying in a side tunnel some feet away had the long hair plucked from its back and sides. In and close about the nest were found forty-three front parts of mice skulls which had evidently been discarded because of the sharp teeth in the maxillaries. Seven full stomachs and eleven hind feet of adult _Microtus_ with parts of leg bones were disclosed in, or under, the weasel's bed and a few small bits of skin with hair attached were scattered among the plucked hair of the nest.

"This weasel seems to have been rather remiss in its sanitary habits as its pile of dung was almost, or quite, touching the nest and only just to the side of its entrance. It was composed of 117 voids all of which contained much hair and broken bone.

"Six other mouse nests found in the same stack, or others adjoining it, had been thinly lined with hair. One of these had two mice in it, a red-backed with its brain eaten out and a _Microtus_ with some hair plucked from its neck. Another nest contained the front part of a skull with teeth and the hind feet and tail of a red-back. Besides the mice found in the nests seven others were discovered tucked away in side tunnels. One of these mice had most of the hair plucked from its back. Whether all these mice and nests belonged to the same weasel or not I am unable to say, but it is usual for them to have several nests in the area surrounding the one that is used as their headquarters or home."

=Mustela rixosa eskimo= (Stone)

Least Weasel

Plates 14 and 15

_Putorius rixosus eskimo_ Stone, Proc. Acad. Nat. Sci. Philadelphia, 1900:44, March 24, 1900.

_Putorius (Gale) vulgaris_, Coues, Fur-bearing animals, p. 102, 1877 (part).

_Putorius rixosus Bangs_, Proc. Biol. Soc. Washington, 10:21, February 25, 1896 (part); Merriam, N. Amer. Fauna, 11:14, June 30, 1896 (part).

_Mustela rixosa eskimo_, Miller, U. S. Nat. Mus. Bull., 79:96, December 31, 1912; Swenk, Journ. Mamm., 7:327, November 23, 1926; Hall, Univ. California Publ. Zoöl., 30:421, March 19, 1929.

_Type._--Female, age in question, no. 848 in Acad. Nat. Sci. Philadelphia; Point Barrow, Alaska; July 25, 1898; obtained by E. A. McIlhenny. Type not seen by me.

_Range._--Alaska and Yukon Territory. See figure 28 on page 180.

_Characters for ready recognition._--Differs from _M. r. pygmaea_ of eastern Asia in longer tail, averaging 11 rather than 16 per cent of length of head and body, and in study skins reaching only to heel instead of to point between heel and toes; from _M. r. rixosa_ in shorter tail averaging 16 rather than 19 per cent of length of head and body and not extending beyond outstretched hind feet in study skins; white of underparts extending dorsally as a reëntrant angle from upper lip to behind eye, rather than delimited dorsally by a boundary between white and brown color that extends straight across cheeks from upper lip to side of body well below eye and ear; breadth of rostrum measured across lacrimal processes more, instead of less, than 85.5 per cent of orbitonasal length; from _M. erminea_ of same region by basilar length of skull less than 32; tail less than 50 and lacking black pencil.

_Description._--_Size._--Male: The original describer lists measurements of topotypes as follows: Total length, 204, 230; length of tail, 28, 31; length of hind foot, 20, 22. Allowing 5 per cent for shrinkage, the hind feet of 5 topotypes yield an average measurement of 23 for the hind foot.

Female: Measurements of two topotypes are: Total length, 184, 180; length of tail, 25, 25; length of hind foot, 24, 18. In four other topotypes the hind feet, allowing 5 per cent for shrinkage, yield an average of 21.

_Color._--Winter pelage all white, rarely with few white hairs in tip of tail but no black pencil; summer pelage with upper parts about Raw Umber and tone 3 of Chocolate pl. 343 of Oberthür and Dauthenay; underparts white, extending over upper lip, insides of limbs and over all four feet. Line of demarcation between underparts and upper parts extends from upper lip posterodorsally to behind eye down to base of ear, up behind ear for a third or more of its height, and back along side of body. Tail unicolor all around and same color as upper parts. Least width of color of underparts averaging 83 per cent of greatest width of color of upper parts.

_Skull._--Based on topotypes; see measurements and plates 14 and 15; weight, 0.82 (0.74-0.93) grams in males, and 0.80 and 0.84 in two females; basilar length, 29.5 (27.6-30.1) in males and 27.8 (27.1-28.8) in females; otherwise as described in _M. e. richardsonii_.

_Remarks._--Among the earliest specimens preserved was one by Edward W. Nelson in the course of his explorations of the Upper Yukon, and one in 1874 by L. T. Turner from St. Michaels, Alaska. Bangs, in 1896 (p. 22) mentioned the occurrence of the species in Alaska, but it was not until 1900 (p. 44) that Stone named the subspecies, and then principally on the basis of specimens obtained two years before by E. A. McIlhenny.

The large size, broad skull, light color and short tail are the distinguishing subspecific characters of the race _eskimo_, and the three characters first mentioned are distinguishing features also of the subspecies of _Mustela erminea_, namely _arctica_, which inhabits the same region. Possibly _eskimo_ also will be found on Banks Island and the other Arctic islands between Alaska and Greenland, as is _M. e. arctica_; at the present time no specimens of _Mustela rixosa_ are known from these islands although some race of rixosa would be expected to occur there.

Animals from southern Alaska average slightly smaller than those from northern Alaska, and this decrease in size toward the south probably represents intergradation with _M. r. rixosa_. Further evidence of intergradation is furnished by the short tail of the specimen from 15 miles east of Atlin; in other particulars this specimen agrees with the subspecies _rixosa_ to which it is here referred. Nevertheless, the short tail, and color pattern, namely reëntrant angle of white behind the eye, is to be seen in all Alaskan specimens examined in the brown pelage, even in no. 107591, from Tyonek on Cook Inlet, which Osgood (1901:69) and Swenk (1926:323) thought might not differ from the subspecies _M. r. rixosa_.

Each of four male topotypes, hardly subadult in age, probably of a single litter, is much larger than any other specimen seen from Point Barrow. The basilar length, for example, is 31.9 as against 29.5, and the weight of the skull (with lower jaws) is as much as 1.5 grams, as against 0.93 in the heaviest of the other males. Initial examination of materials from Point Barrow raised the suspicion that two distinct species were represented--_rixosa_ and a larger one possibly allied to _M. nivalis_ of the Old World. Nevertheless, further study almost completely allayed the suspicion because the only difference discernible is one of size, and it is supposed that additional specimens will bridge the gap in size and show that _M. r. eskimo_ at Point Barrow averages larger than the adult specimens now available indicate. The four large males of subadult age are nos. 42814-42816 and 42818 of the American Museum of Natural History.

Of the fourteen adult and subadult skulls examined, two display lesions resulting from infestation of the frontal sinuses by nematode parasites. None of the young skulls show such infestation.

_Specimens examined._--Total number, 42 as follows. Arranged alphabetically by Territory and District and unless otherwise indicated in the United States National Museum.

=Alaska.= Barrow and Point Barrow, 19 (8[2] 7[74], 2[1], 1[50]); Wainwright, 1[57]; Mts. back of Icy Cape, 1[77]; west of Beechey Point, 1[2]; west edge of Colville River Delta, 1[2]; Koyukuk River, 16 mi. above Beetles, 1; upper Yukon, 1; Fort Yukon, 1; Stephens Village, 1; Wales, 1[57]; McDonald Creek, tributary of Salcha Slough, 1; near head of Toklat River, 1; head of Kantishna River, 1; St. Michael, 4 (2[74]); Tyonek [= Tyonek], 1; Bethel, 3; vic. Bristol Bay, 1.

=Yukon.= La Pierre's House, 1; Klotassin River, tributary of White River, 1.

=Mustela rixosa rixosa= (Bangs)

Least Weasel

Plates 14 and 15

_Putorius rixosus_ Bangs, Proc. Biol. Soc. Washington, 10:21, pl. 1, fig. 6, pl. 2, fig. 6, pl. 3, fig. 4, February 25, 1896; Merriam, N. Amer. Fauna, 11:14, pl. 2, figs. 7, 7a, June 30, 1896.

_Putorius pusillus_, Baird, Mamm. N. Amer., p. 159, 1858.

_Putorius (Gale) vulgaris_, Coues, Fur-bearing animals, p. 102, 1877.

_Mustela rixosa_, Thomas, Proc. Zoöl. Soc. London, p. 168, March, 1911.

_Mustela rixosa rixosa_, Miller, U. S. Nat. Mus. Bull., 79:96, December 31, 1912; Swenk, Journ. Mamm., 7:327, November 23, 1926.

_Type._--Female, adult, skin and skull; no. 642 Bangs Coll. in Mus. Comp. Zoöl.; Osler, Saskatchewan; July 15, 1893; obtained by W. C. Colt; original no. 79 according to describer.

The skull lacks the basioccipital, basisphenoid, and left zygomatic arch. The "crowns" of the lower canines are missing; otherwise the teeth are present and entire. The skin is fairly well made, with soles of hind feet up, in good condition and in summer pelage.

_Range._--From northern British Columbia and Great Slave Lake south on the west side of the Rocky Mountains to Ootsa Lake, British Columbia, and on the east side of the Rocky Mountains, south to central Montana, North Dakota and Minnesota; eastward in Canada, entirely north of St. Lawrence River, to Atlantic Ocean. See figure 28 on page 180.

_Characters for ready recognition._--Differs from _M. r. eskimo_ in longer tail averaging 19 rather than 16 per cent of length of head and body and extending beyond outstretched hind feet in study skins, rather than to a point short of tips of toes; boundary between brown upper parts and white underparts extending straight across cheeks from upper lip to side of body well below eye and ear, rather than with reëntrant angle from upper lip carrying white upward to point behind eye, and with breadth of rostrum less, instead of more, than 85.5 per cent of orbitonasal length; from _M. r. campestris_ by smaller size: hind foot less than 25 in males and ordinarily less than 22 in females; in males total length less than 216 and tail averaging less than 34, and in females total length averaging less than 182 and tail averaging less than 29; color said to average darker; from _M. r. allegheniensis_ by three average differences, namely lighter color, longer tympanic bullae and larger size of males; from _M. frenata_ and _M. erminea_ of same region by basilar length of skull less than 32; tail less than 50, and lacking black pencil.

_Description._--_Size._--Male: Six adults and subadults from Shaunavon, Saskatchewan, yield average and extreme measurements as follows: Total length, 202 (188-208); length of tail, 32.5 (31.5-34.0); length of hind foot, 22.8 (21-24).

Female: One adult and 3 subadults from the same area yield average and extreme measurements as follows: Total length, 172 (162-190.5); length of tail, 27.4 (24-34); length of hind foot, 19.6 (17.5-22).

_Color._--Winter pelage all white, rarely brown; as described in _M. r. eskimo_ except that line of demarcation on side of head between upper parts and underparts passes almost straight back without the dorsally directed reëntrant area of white behind the eye and ear; least width of color of underparts averaging 52 per cent of greatest width of color of upper parts.

_Skull_ (Based on those from Shaunavon, Sask.)--See measurements and plates 14 and 15; weight, 0.88 (0.70-0.98) grams in males and 0.55 (0.54-0.56) in females; basilar length, 29.5 (28.4-30.4) in males and 26.1 (24.7-27.0) in females; otherwise as described in _M. e. richardsonii_.

_Remarks._--As early as 1858 (p. 159) Baird recognized an individual of this race from Pembina, Minnesota, as pertaining to a distinct species. Although he used for it the specific name _pusillus_ originally proposed by DeKay for a small weasel from the state of New York, Baird wisely noted that the specimen he described "may be different from the New York species. . . ." After preparing this account, Baird included a second specimen, from Fort Steilacoom, Washington Territory, which he thought might be the same, but the differences that he was careful to point out, in the light of later knowledge, show it to be of the species _Mustela erminea_. Only a few other naturalists followed Baird in distinguishing the least weasel as a separate species until Bangs in 1896 (p. 21) clearly differentiated it and proposed for it the name _Putorius rixosus_, which continues in use today and applies to the species.

The accumulation at the National Museum of Canada, through the energy of Dr. R. M. Anderson, of a good series of specimens from Saskatchewan in the general vicinity of the type locality allows for the first time an adequate conception of the amount of secondary sexual variation and individual variation and permits recognition of subspecific characters to differentiate between _M. r. rixosa_ and the subspecies _eskimo_ and _campestris_. In comparison with the subspecies _allegheniensis_ the basis for segregation is less clear and will remain somewhat in doubt until additional adults of _allegheniensis_ from, say, Pennsylvania, become available with accurate external measurements taken in the flesh and especially with complete skulls.

Intergradation with the subspecies _eskimo_ is suggested by the short tail of the specimen from fifteen miles east of Atlin, British Columbia; in other particulars that specimen, a skin-alone, agrees with the subspecies _rixosa_. Intergradation with _campestris_ is indicated by increased size of some specimens from North Dakota, and is suggested with _allegheniensis_ by the color of specimens from Wisconsin and Illinois. Three specimens from Winona County, in southeastern Minnesota, unfortunately are skulls-alone without external measurements. Also, two of these skulls are of young animals. The one adult, unsexed, is from Crystal Springs. Selected cranial measurements are: basilar length, 28.5; length of tympanic bulla, 10.9. These measurements accord with those of males of the subspecies _rixosa_ to which the specimens from Winona County, therefore, are here assigned. The possibilities have not been excluded, however, that the adult is an unusually large female of the subspecies _campestris_ or a male of _allegheniensis_ that has tympanic bullae longer than average for that subspecies.

Some hesitation is felt in assigning the specimens, 8 in all, from eastern Canada to the subspecies _rixosa_. The skin-alone from Eagle River and the skin, with part of the skull, from St. Michael Bay, are in transitional pelage and are of no help in appraising subspecific characters. The one adult specimen which does have a complete skull is from an island south of the Comb Hills. This animal in all respects agrees with selected individuals of _M. r. rixosa_ from Saskatchewan, but each of the five other skins in summer pelage has spots of dark brown color on the breast. Only about one specimen in three of _rixosa_ from Saskatchewan is similarly marked. Furthermore, on some of the specimens from eastern Canada the spots are larger than on any of the animals from farther west. The greater frequency of brown spots on the breast, the larger average size of these spots, and the darker average coloration of the upper parts are suggestive of geographic variation, the existence of which has to be proved by additional and more complete specimens from eastern Canada. For the time being, specimens from there are tentatively assigned to the race _rixosa_.

Of 56 subadult and adult skulls only 3 (1 North Dakota; 1 Calgary, Alberta; and 1 Island S Comb Hills, Queb.) display lesions resulting from infestation of the frontal sinuses by nematode parasites. None of the young skulls shows such infestation.

_Specimens examined._--Total number, 87 as follows. Arranged alphabetically by provinces and states and within each from north to south. Unless otherwise indicated, specimens are in the United States National Museum.

=Alberta.= Miette River, 1[77]; 5 mi. NW Camrose, 1[77]; Camrose, 2 (1[77], 1[31]); "near Camrose," 2[77]; Forks Blindman and Red Deer rivers, 1[60]; Innisfail, 1[86]; Veteran, 1[93]; Diddsbury [= Didsbury], 1; Calgary, 2 (1[93], 1[2]); Shepard, 1[86].

=British Columbia.= Clarks Ranch, Halfway River, Peace River Dist, 1[85]; 15 mi. E Atlin, 1[8]; Wistaria, P. O., 3 (2[77], 1[85]); Ootsa Lake, 1[85].

=Labrador.= Davis Inlet, 1[60]; 30 mi. upriver and 20 mi. toward Groswater Mts., Eagle River, 1; St. Michael Bay, 1.

=Mackenzie.= Old Fort Reliance, 1[2]; Fort Resolution, 2; Fort Smith, 1.

=Manitoba.= Gypsumville, 1[86]; Lake St. Martin Reserve, 1[86].