American Weasels

Part 1

Transcribers Notes:

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Greek text has been transliterated and are denoted by ~tildes~.

Male and Female symbols are represented by and 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

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

In regions of heavy rainfall (see figs. 2 and 3) there is an increase in pigmentation and extent of blackish color backward over the neck and a decrease in extent of the white facial markings. In regions progressively more arid (see figs. 3 to 7) there is a decrease in pigmentation and extent of blackish color and an increase in extent of the white facial markings.

As shown by rearing mammals from humid regions in arid regions, and vice versa, the color is not visibly altered in one or a few generations; the color is an hereditary character. Beginning with the southernmost subspecies (fig. 1) and continuing northward to the northern subspecies (fig. 10) there is a darkening, next a lightening, and finally a darkening closely conforming to amounts of precipitation in the geographic regions concerned. A fuller discussion of this correlation is given on page 51.]

American Weasels

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

Part 2

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.

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