Part 1
Transcribers Notes:
Italics words are denoted by _underscores_. Bold words are denoted by =equals=.
Whole and fractional parts are displayed as 7-3/4.
Greek text has been transliterated and are denoted by ~tildes~.
Male and Female symbols are represented by [M] and [F] respectively.
UNIVERSITY OF KANSAS PUBLICATIONS MUSEUM OF NATURAL HISTORY Vol. 4, pp. 1-466, plates 1-41, 31 figures in text December 27, 1951
AMERICAN WEASELS
BY
E. RAYMOND HALL
UNIVERSITY OF KANSAS LAWRENCE 1951
UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY
Editors: E. Raymond Hall, Chairman, A. Byron Leonard, Edward H. Taylor, Robert W. Wilson
Vol. 4, pp. 1-466, plates 1-41, 31 figures in text
December 27, 1951
UNIVERSITY OF KANSAS Lawrence, Kansas
PRINTED BY FERD VOILAND, JR., STATE PRINTER
TOPEKA, KANSAS 1951
23-3758
American Weasels
BY
E. RAYMOND HALL
CONTENTS
PAGE
INTRODUCTION 7
PALEONTOLOGICAL HISTORY 10
SKELETON AND DENTITION 12
DISPARITY IN NUMBERS OF MALES AND FEMALES 19
MATERIALS, ACKNOWLEDGMENTS AND METHODS 21
VARIATION 24 Variation with Age 24 Secondary Sexual Variation 26 Individual Variation 28 Seasonal Variation 30 Variation in Coloration and Molt 30 Variations of Taxonomic Worth 44
DISTRIBUTION AND SPECIATION 54
HISTORY OF CLASSIFICATION 69 Chronological List (annotated) of Specific and Subspecific Names Applied to American Weasels 71
CHECK-LIST OF AMERICAN SPECIES AND SUBSPECIES OF THE GENUS MUSTELA 81
ARTIFICIAL KEY TO AMERICAN SPECIES OF THE GENUS MUSTELA 83
DIAGNOSIS OF THE GENUS 83
EXPLANATION OF SYSTEMATIC TREATMENT 84
SYSTEMATIC ACCOUNTS OF SPECIES AND SUBSPECIES 87 _Mustela erminea_ 87 _Mustela rixosa_ 168 _Mustela frenata_ 193 _Mustela africana_ 406
EXPLANATION OF CRANIAL MEASUREMENTS 417
TABLE OF CRANIAL MEASUREMENTS 418
LITERATURE CITED 442
INDEX 461
American Weasels
By E. RAYMOND HALL
INTRODUCTION
The weasel's agility and speed take it in and out of retreats, over obstacles and across open places in amazingly rapid fashion and are responsible for the animal's actions being described as "quick as a flash." The common long-tailed weasel of the United States measures approximately a foot and a half in length, of which the tail comprises a third; but the round, slender body is scarcely more than an inch and a half in diameter. Brown above and whitish below in summer dress, the animal is sleek as well as lithe and graceful. It is easy to understand, therefore, why the Bavarian name _Schönthierlein_ (pretty little creature) and the Italian name _donnola_ (little lady) were bestowed upon it. The Spanish name is _comadreja_ (godmother).
In the winter, in temperate and northern regions, the coat becomes pure white except for the black tail-tip. In this dress the correct name for the animal is ermine, a mammal whose fur is known to all and justly esteemed, especially for its luster in artificial light, where it is scarcely excelled in enhancing the beauty of gems and their feminine wearers.
In relation to its weight, the weasel is thought to be unsurpassed, and perhaps it is unequalled among mammals, in the effectiveness with which it exercises its carnivorous heritage; it kills with speed and strength a wide variety of animals including many much larger than itself; and it has been known to attack even man himself when he stood between the weasel and its intended prey. In structure and temperament it is so highly specialized for offense that, when opportunity affords, it sometimes kills, for storage in its larder, far more than enough to meet its immediate needs. After speaking of this tendency, Elliott Coues (1877:129) has said:
"A glance at the physiognomy of the weasels would suffice to betray their character. The teeth are almost of the highest known raptorial character; the jaws are worked by enormous masses of muscles covering all the side of the skull. The forehead is low and the nose is sharp; the eyes are small, penetrating, cunning, and glitter with an angry green light. There is something peculiar, moreover, in the way that this fierce face surmounts a body extraordinarily wiry, lithe, and muscular. It ends in a remarkable long and slender neck in such a way that it may be held at right angle with the axis of the latter. When the creature is glancing around, with the neck stretched up, and flat triangular head bent forward, swaying from one side to the other, we catch the likeness in a moment--it is the image of a serpent." Although Coues' colorful description more closely links the weasel with the symbol of evil than pleases me, his description does emphasize the raptorial character of the weasel.
Even though most weasels are intractable as pets, they have a value to man, as, for instance, when he is plagued by mice. In a field where mice and other small rodents are so abundant as to damage cultivated crops, the weasel is the farmer's best friend. A weasel may inhabit one den until the rodents thereabouts are almost exterminated in an area two or three hundred yards across; in this way the weasel acts as a control, locally, as well as a check more widely, on the increase in size of populations of kinds of rodents upon which it preys. The smaller species are mousers of remarkable efficiency and can, if necessary, follow a mouse to the end of the mouse's burrow. The slender body allows the weasel to pass through any burrow or hole into which it can thrust its head. This ability in an organism as highly specialized for killing other animals as is the weasel, has earned for it a bad name in connection with poultry yards. Authentic instances are recorded in which a weasel, gaining entrance through a knot-hole to a coop of young chickens, killed several dozen of the fowls. In other instances, however, weasels have lived under buildings close by a poultry yard without even molesting the birds in the slightest; in the latter instances the weasels probably were present because there was an abundant supply of rats and mice. At least three poultry raisers (see page 214) have encouraged weasels to live in their poultry yards feeling that the good they do by destroying rats outweighs the damage caused by the occasional weasel which turns to the fowls; the idea is that the individual weasel can be eliminated if he becomes destructive.
Although tending to be nocturnal, weasels are almost as active by day as by night. Their young, numbering 4 to 9, are born in a nest in a burrow and as with other members of the Order Carnivora, are blind, and incapable of looking after themselves at the time of birth. In _Mustela frenata_ of Montana, breeding occurs in July and August, and the young are born in the following April and May. Wright (1948A:342) showed that the gestation period could not have been less than 337 days in one individual and that it averaged 279 (205-337) days in 18 instances. Findings of the same author (1942B:109) showed that the embryos are implanted only 21 to 28 days before the young are born. In the preceding part of the "long gestation period, the embryos lie dormant in the uterus as un-implanted blastocysts. The young female weasel [of _M. frenata_] mates when 3 or 4 months old." Consequently, in the spring, all females of this species may produce young (Wright, 1942A:348). The circumboreal species _Mustela erminea_ likewise has been shown to have a delayed implantation of the ova. Each of these two species, _M. frenata_ and _M. erminea_, has only one litter per year; but the weasel, _Mustela nivalis_, of the Old World seems to lack the delayed implantation, in this respect resembling the ferret (subgenus _Putorius_) as it does also in its ability to have more than one litter per year (see Deanesly, 1944). The manner of reproduction in the South American species _M. africana_ and the circumboreal species _M. rixosa_ at this writing is unknown.
The genus _Mustela_ includes the true weasels, the ferrets and minks. The ferrets commonly are treated as a subgenus, _Putorius_, along with the Old World polecat. The minks usually are accorded subgeneric distinction under the name _Lutreola_, and the true weasels comprise the subgenus _Mustela_, the three subgenera together, along with some other subgenera which are mostly monotypic, comprising the genus _Mustela_. Considered in this way, the group of true weasels, subgenus _Mustela_, has a geographic range roughly coextensive with that of the genus _Mustela_. This range includes Asia and Europe, Northern Africa, North America and northern South America. Java has its weasel. Australia and nearly all the oceanic islands lack weasels, and the animals are absent from roughly the southern half of Africa and the southern half of South America. Other small mustelids, weasellike in shape and with corresponding habits and dentition, take the place of true _Mustela_ in the southern half of Africa and in the corresponding part of South America.
In America the subgenus _Mustela_ occurs from the northernmost land in Arctic America southward to Lake Titicaca in the Andes of South America, a distance of approximately 6900 miles. _Felis_, I think, is the only other genus of land mammals in the western hemisphere that has a geographic range as extensive from north to south. _Felis_ does not range so far north but does range farther south. The one species, _Mustela frenata_, ranges from Lake Titicaca northward to about 57° N in British Columbia or for approximately 5000 miles in a north to south direction and from within the Alpine Arctic Life-zone through the Tropical Life-zone. In North America, weasels occur in almost every type of habitat, being absent only in the extremely desert terrain of western Arizona and western Sonora and in adjoining parts of California and Baja California. Even this area, along the Colorado River, may support some weasels; evidence suggesting that it does so is given in the account of _Mustela frenata neomexicana_.
PALEONTOLOGICAL HISTORY
The paleontological record fails to show the precise ancestry of _Mustela_. The genus has been found in deposits of Pleistocene age, but, so far as I can ascertain, not in deposits of earlier times. The Pleistocene remains are not specifically distinct from Recent (living) species, and in only a few instances (see _M. f. latirostra_ and _M. e. angustidens_) are they even subspecifically distinct from the Recent weasel living in the same area today. It is true that fossil remains from deposits of several stages of the Tertiary beds have in the past been identified in the literature as _Mustela_, but most of these identifications were made many years ago when the generic name _Mustela_ was used in a far broader and more inclusive sense than it is today and much of the fossil material was so fragmentary that the generic identity could not be ascertained, at least at that time. Because the generic identity could not be ascertained, the fossil material was tentatively assigned to the genus _Mustela_, the "typical" genus of the family Mustelidae instead of to some other more specialized or less well-known genus of the family. To satisfy my curiosity about these species of "_Mustela_" of a geological age earlier than the Pleistocene I have personally studied nearly all of the original specimens from North America and have found each to be of some genus other than _Mustela_. Also, such study as I have been able to make of the Old World fossils themselves that have been referred to the genus _Mustela_ up to 1938, and my study of the illustrations and descriptions of the others from there lead to the same conclusion; that is to say, none that is true _Mustela_ is known up to now from deposits older than the Pleistocene.
When, in 1930 (pp. 146-147), I wrote about the taxonomic position of three American genera of fossils (known only from lower jaws), each of which had been previously referred to the genus _Mustela_, I said that they pertained "to that section of the weasel family (Mustelidae) which comprises the polecats, true weasels, ferrets, minks and martens. The fossil specimens . . . are smaller than any other later Tertiary members of the group yet described, and are more primitive than any of the above mentioned Recent relatives. Of the three extinct genera . . . _Miomustela_ [Lower Pliocene or Upper Miocene of the Lower Madison Valley, Montana] is the most primitive and _Martinogale_ [Pliocene, 18 mi. SE Goodland, Sherman County, Kansas] is the most advanced. This view rests largely on the character of M_{=1} which in _Miomustela_ has a deeply basined, short, narrow talonid with a thick, high metaconid situated partly posterior to the protoconid. In _Martinogale_ the talonid is incipiently trenchant, long, broad, and it has a lesser developed metaconid which is situated more anterior [ly]. _Pliogale_ [Lower Pliocene, Humboldt County, Nevada] is intermediate in this respect.
"These three forms are of special interest as possible ancestors of the subgenus _Mustela_, true weasels. No members of this subgenus, nor related forms which can with any degree of certainty be regarded as directly ancestral to them, have yet been described from Miocene or Pliocene deposits. _Palaeogale_ of the Old World and _Bunaelurus_ of North America, each of Oligocene age, have been placed by Schlosser (1888, p. 116) and Matthew (1902, p. 137) as members of the primitive group of mustelids ancestral to _Mustela_. This course seems logical; and with no truly intermediate links between these forms of the Oligocene on the one hand, and _Mustela_ which first appears in the Pleistocene, on the other, more definite statements about ancestral positions of the small Oligocene forms can hardly be made. The deciding considerations for authors who placed _Palaeogale_ and _Bunaelurus_ as ancestral to _Mustela_ were the absence of a metaconid on M_{1} and the trenchant talonid of that tooth. These characters are found also in _Mustela_. On the other hand certain structures in the basicranial region of _Palaeogale_ and more especially of _Bunaelurus_ indicate that these genera possibly are not close to the ancestral form of Mustela . . . _Martinogale_ may stand near the ancestral form of _Mustela_ and . . . _Pliogale_ may be ancestral to _Martinogale_. _Pliogale_, in turn, may have had an ancestor similar to _Miomustela_. If this should prove to be the case, _Palaeogale_ and _Bunaelurus_ might be regarded as an independent branch which displays merely a parallelism to _Mustela_ in the loss of the metaconid on M_{1} and the development of a trenchant talonid on that tooth. The writer would make it clear that he does not hold such to be the case. The ancestral relation of _Martinogale_ to _Mustela_ is presented merely to show the possibility, and not the special probability, of such an origin for _Mustela_. Knowledge of the tympanic bullae and other structures of the basicranial region would go far toward answering the question and until these structures are known [in mustelids of the Later Tertiary,] some uncertainty will remain."
At the present writing I can add to the above statement only a few facts. The discovery of better material of _Bunaelurus_ than was available to previous workers led Simpson (1946), correctly I think, to synonymize _Bunaelurus_ with _Palaeogale_. Simpson figures the cranial foramina in _Palaeogale_. The differences, between _Palaeogale_ and _Mustela_, in cranial foramina, possibly are only the result of the elongation of the tympanic bullae. The bullae of the subgenus _Mustela_ are seen to be much elongated posteriorly if comparison is made with the bullae of earlier mustelids. Consequently, it might be concluded that there is nothing in the arrangement of the cranial foramina which would preclude the derivation of _Mustela_ from _Palaeogale_. However, the anterior situation of the carotid foramen--well forward along the medial margin of the tympanic bulla--is a character typical of other mustelids and the posterior location of this foramen in _Palaeogale_ might indicate that it was not ancestral to _Mustela_.
SKELETON AND DENTITION
The outstanding features of a weasel's skeleton are its length and slenderness. Whereas the length of the vertebral column measured from the atlas (the first cervical vertebra) to the last sacral vertebra is 175 per cent of the length of the hind leg (as measured from the head of the femur to the tip of the longest claw), the corresponding percentage is only 116 in the raccoon. Stated in another way, the vertebral column and the hind leg are of approximately equal length in a raccoon, but in a weasel the vertebral column is one and three-fourths times as long as the hind leg.
VERTEBRAE
The vertebral column consists of 7 cervicals, and ordinarily 14 thoracics, 6 lumbars, 3 sacrals and, depending on the species, 11 to 23 caudals. For the three species of which skeletons were examined, variations from the normal number of vertebrae are noted in the following table:
TABLE I
Data on vertebrae in three species of the subgenus Mustela (Numerals in parentheses indicate number of specimens)
===================+=========+=========+========= |_Mustela_|_Mustela_|_Mustela_ |_erminea_| _rixosa_|_frenata_ -------------------+---------+---------+--------- Number of cervical | (75) | (12) | (65) vertebrae | 7 | 7 | 7 -------------------+---------+---------+--------- Number of thoracic | (71) | (12) | (54) vertebrae | 14 | 14 | 14 +---------+---------+--------- | (4) | | (13) | 15 | | 15 -------------------+---------+---------+--------- The dorsal vertebra| (18) | (12) | (40) constituting the | 11th | 11th | 11th anticlinal +---------+---------+--------- | (7) | | (27) | 12th | | 12th -------------------+---------+---------+--------- Number of lumbar | (2) | | (11) vertebrae | 5 | | 5 +---------+---------+--------- | (73) | (12) | (54) | 6 | 6 | 6 -------------------+---------+---------+--------- Number of sacral | (9) | | (3) vertebrae | 2 | | 2 +---------+---------+--------- | (65) | (10) | (67) | 3 | 3 | 3 +---------+---------+--------- | (1) | (2) | | 4 | 4 | -------------------+---------+---------+--------- Number of | (73) | (12) | (57) pseudosacral | 0 | 0 | 0 vertebrae +---------+---------+--------- | (2) | | (6) | 1 | | 1 -------------------+---------+---------+--------- | | (1) | | | 11 | +---------+---------+--------- | | (3) | | | 14 | +---------+---------+--------- | (2) | (7) | | 15 | 15 | +---------+---------+--------- | (3) | (1) | | 16 | 16 | +---------+---------+--------- | (9) | | | 17 | | +---------+---------+--------- Number of caudal | (28) | | vertebrae | 18 | | +---------+---------+--------- | (11) | | (6) | 19 | | 19 +---------+---------+--------- | | | (14) | | | 20 +---------+---------+--------- | | | (14) | | | 21 +---------+---------+--------- | | | (7) | | | 22 +---------+---------+--------- | | | (1) | | | 23 -------------------+---------+---------+---------
Variation according to the species is evident in the number of caudal vertebrae, but in the other categories of vertebrae no consistent difference in number according to species was found in the material examined. Apparently there is also some geographic variation in the number of caudal vertebrae within a species. For example, the one skeleton seen of _Mustela rixosa eskimo_ (no. 219036, U. S. Nat. Mus., from St. Michaels, Alaska) has only 11 caudal vertebrae, whereas in the 11 _Mustela rixosa rixosa_ from Roseau County, Minnesota, the usual number is 15 with extremes of 14 and 16. Similarly specimens of _Mustela frenata_ from Idaho and California almost always have 1 or 2 more caudal vertebrae than do individuals of the shorter-tailed subspecies of the same species from eastern Kansas.