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.
[Illustration: FIG. 28. Map showing occurrences and probable geographic
ranges of the subspecies of _Mustela rixosa_ in North America.]
"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].
=Minnesota.= _Roseau County_: Cedarbend, 2[14]; Grimstad, 1[14];
America, 2 (1[14], 1[74]); Malung, 1[74]; Norland, 1[41]; Falun, 3
(1[14], 1[74], 1[41]); Palmville, 1[41]; Spruce, 1[74]; Stokes,
1[74]. No locality more definite than Marshall County, 1[14].
_Clay County_: Moorhead, 1[36]. _Winona County_: "near" Whitman,
1[34]; Altura, 1[98]; Crystal Springs, 1[98].
=Montana.= Sun River Valley, 1; Wibaux in Wibaux County, 1.
=North Dakota.= _Walsh County_: Grafton, 15 (3[60], 1[93], 5[2],
2[14], 1[74], 1[1], 1[76]). _McHenry County_: 4 and 4-1/2 mi. N
Upham, 2. _Wells County_: 1[36]. _Morton County_: Mandan, 1[60].
=Ontario.= Algoma Dist: Tatnall, near Oba, 1[86]. Moose Factory,
1[75].
=Quebec.= Island S of Comb Hills, James Bay, 1[9]. _Saguenay
County_: Natashkwan, 1.
=Saskatchewan.= Osler, 1[75]; "near Regina," 1[77]; Dollard,
2[31]; Shaunavon (and "near" and 1 mi. NE), 9[77]; Klintowel P. O.
(about 15 mi. N of Eastend), 1[77]; Eastend and "near" Eastend,
2[77].
=Mustela rixosa allegheniensis= (Rhoads)
Least Weasel
Plates 14, 15 and 41
_Putorius allegheniensis_ Rhoads, Proc. Acad. Nat. Sci.
Philadelphia, 1900:751, March 25, 1901.
_Putorius rixosus allegheniensis_, Cory, Mamm. Illinois and
Wisconsin, p. 378, 1912.
_Mustela allegheniensis_, Miller, U. S. Nat. Mus. Bull., 79:96,
December 31, 1912.
_Mustela rixosa allegheniensis_, Swenk, Journ. Mamm., 7:328,
November 23, 1926.
_Type._--Probably male adult, skin and skull, no. 6195, Acad. Nat.
Sci. Philadelphia; near Beallsville, Washington Co., Pa.; about
1885 or 1886; obtained by Robert Hawkins.
Type not seen by me.