A Synopsis of the North American Lagomorpha.

by E. Raymond Hall.

The most popular small game mammal in nearly every part of North America is one or another of the species of rabbits or hares. The rabbit is one of the few species of wild game that still is hunted commercially and sold for food on the open market. The close a.s.sociation and repeated contact of man with these animals has resulted in his contracting such of their diseases as are transmissible to him. Consequently the rabbits and hares have figured in many investigations concerned with public health and medicine. Because the number of such investigations is increasing, there has been an increasing number of specimens of these animals submitted to mammalogists for identification; also, inquiries are received as to the degree of relationship between two or more of the named kinds of rabbits in which identical, or closely related, disease organisms have been found; other inquiries have to do with the degree of relationship of named kinds of rabbits and hares in widely separated parts of the continent.

The monographs to which the investigator could turn to obtain answers to some of these questions are Arthur H. Howell's "Revision of the American Pikas" (1924), and Edward H. Nelson's "The Rabbits of North America"

(1909) published 27 and 42 years ago, respectively. These monographs are still excellent sources of detailed information, as, of course, also is Marcus Ward Lyon's "Cla.s.sification of the Hares and their Allies"

(1904). The acquisition of additional study specimens in recent years, however, has provided new data on the geographic occurrence of several species, and study of these specimens has given basis for a different arrangement of several named kinds of the lagomorphs. Two princ.i.p.al aims of the present synopsis, therefore, are to combine in one publication the current taxonomic arrangement and as much as is known of the geographic distribution of the several species and subspecies.

The maps herewith and listings of marginal localities are the means chosen to present the information on geographic distribution. The artificial key is supplemented by line drawings of skulls of certain species and by a minimum of text to aid the user of the key. The skulls are necessary for the identification of some species of the genus _Sylvilagus_. The skins, on the contrary, are essential for the identification of the species of the genus _Lepus_ in central Mexico and in the Great Basin of the western United States. Consequently, it has been impossible to construct a key based on external characters only or on cranial features only. Furthermore, the only apparent differences between a given pair of species in one region may not be apparent in another region where the same two species occur together. A case in point is provided by _Sylvilagus florida.n.u.s_ and _Sylvilagus nuttallii_ where the Great Plains meet the eastern flank of the Rocky Mountains and where the Sonoran desert meets the southwestern flank of these mountains. The details are described by Hall and Kelson (1951:52, 53) and are indicated in the part of the accompanying artificial key that takes out the species _Sylvilagus nuttallii_. Because of this geographic change in specific characters and because of the slight amount of difference between certain species of leporids, I have frequently resorted to geography, instead of to morphology alone, in constructing the artificial key. Despite this fault of the key to the lagomorphs, it, and the accompanying account, I hope, will aid workers who need to identify kinds of lagomorphs and to know about their geographic distribution.

Another reason for presenting a synopsis of the lagomorphs at this time is that the presentation may bring suggestions for improvement in the arrangement of the kind of information presented here; an account along similar lines for all of the kinds of mammals native to North America is in prospect. Corrections of, and additions to, the material presented here will be welcomed and I shall be especially grateful for suggestions as to a more useful arrangement of the data.

In arranging the families, genera and species the aim has been, in each category, to list the most primitive members first and to list last the one which presents the highest total of specialization. The term _total of specialization_ is used here, as Miller (1924:2) used it, to denote the sum of the physical modifications which any mammal, or taxonomic category of mammals, is supposed by the author to have undergone during the course of its development away from its original or generalized mammalian stock.

Subspecies of any one species are arranged alphabetically. On the maps, of course, the subspecies are shown in their correct geographic positions.

For each subspecies, or species if it has not been divided into subspecies, there is given (1) the accepted scientific name (selected in accordance with the rules of the International Commission of Zoological Nomenclature); (2) a citation to the account in which the terminal part of the name was first proposed (the original description of zoological parlance) followed by a statement of the type locality; (3) a citation to the account in which the combination of names (generic, specific and subspecific) used in the present account first was employed unless the name combination used here is the same as that in the original description; (4) synonyms arranged in chronological order, and (5) marginal record stations of occurrence.

These marginal records are arranged in clockwise order beginning with the northernmost locality. If more than one of the marginal localities lies on the line of lat.i.tude that is northernmost for a given kind of mammal, the westernmost of these is recorded first. The marginal localities that are represented by symbols on the corresponding distribution map are in Roman type. Italic type is used for those marginal localities that could not be represented by symbols on the map because undue crowding, or overlapping, of the symbols would have occurred. An understanding of how these localities are arranged and knowledge as to which of these localities are shown on the map will permit a person to a.s.sociate any symbol on a map with its corresponding place name.

Measurements are in millimeters unless otherwise indicated. Capitalized color terms are after Ridgway (Color Standards and Color Nomenclature, Washington, D. C., 1912), and uncapitalized terms refer to no particular color standard. Several of the drawings of skulls were reproduced originally in the "Mammals of Nevada" (Hall, 1946) and I am grateful to the University of California Press for permission to use them here.

Those drawings were made by Miss Viola Memmler. The other drawings are the work of Mrs. Frieda Abernathy, Mrs. Diane (Danley) Sandidge, and Mrs. Virginia (Ca.s.sel) Unruh. Initials on the drawings identify the individual's work. The study here reported upon was aided by a contract between the Office of Naval Research, Department of the Navy, and the University of Kansas (NR 161-791). Also, a.s.sistance with some of the field work was given by the Kansas University Endowment a.s.sociation and by Dr. Curt von Wedel. For the corrected dates on several publications I am indebted to Dr. A. Remington Kellogg. For a.s.sistance with the organization of the data for the present account I am grateful to several persons, especially to my wife, Mary F. Hall, and to Dr. Keith R. Kelson.

Order LAGOMORPHA--Hares, Rabbits and Pikas

Families and genera revised by Lyon, Smithsonian Miscl. Coll., 45:321-447, June 15, 1904. For taxonomic status of group see Gidley, Science, n. s., 36:285-286, August 30, 1912.

The order Lagomorpha is old in the geological sense; fossilized bones and teeth of both pikas and rabbits are known from deposits of Oligocene age and even at that early time the structural features distinguishing these animals from other orders were well developed.

A noteworthy character of the order is the presence of four upper incisor teeth (instead of only two as in the Rodentia); also, the fibula is ankylosed to the tibia and articulates with the calcaneum. Each of the first upper incisors has a longitudinal groove on its anterior face.

All lagomorphs are herbivorous. They eat princ.i.p.ally leaves and non-woody stems although the bark of sprouts and bushes is taken as second choice by rabbits and hares.

Correlation of structure and function is well ill.u.s.trated among the lagomorphs by the means which the different species employ to detect and escape from their enemies. A gradient series is evident in which the pikas and jack rabbits are the extremes. The black-tailed jack rabbit, for example, in relation to size of the entire animal, has the longest ears and longest hind legs. This kind of lagomorph takes alarm when an enemy, for example, a coyote, is yet a long way off. The jack rabbit seeks safety in running; even when being overtaken by a pursuer that is close behind, the jack rabbit still relies on its running ability instead of entering thick brush or a hole in the ground where its larger-sized pursuer would be unable to follow. A cottontail has shorter ears and shorter hind legs. It allows the enemy to approach more closely than the jack rabbit does before running, and then, although relying in some measure on its running ability for escape, flees to a burrow or thicket for safety from its pursuer. The brush rabbit with ears and hind legs shorter than those of the cottontail seldom if ever ventures farther than 45 feet away from the edge of dense cover. After an enemy is near, the brush rabbit has merely to scamper back into the brush.

Still shorter of ear and hind leg is the pigmy rabbit which ventures outside its burrow to feed only among the tall and closely-s.p.a.ced bushes of sagebrush among which its burrow is dug. Detection of the slightest movement of an enemy on the opposite side of the bush sends the pigmy rabbit, in one or a few jumps, into the mouth of its burrow and, if need be, below ground. The pika, with the shortest ears and legs of all, lives in the rock slides and has to do little more than drop off the top of a rock into a s.p.a.ce between the broken rocks when an enemy is detected near enough to the pika to have a chance of seizing it.

The number of molts in a year, depending on the kind of lagomorph, varies in adults from one (according to Nelson, 1909:31) in the cottontails (genus _Sylvilagus_) to as many as three (according to Lyman, 1943, and Severaid, 1945) in the varying hare (_Lepus america.n.u.s_). Difficulties that I have experienced in attempting to account for the variations in color and wear of the pelage of the pika, _Ochotona princeps_, on the basis of two molts per year, make me wonder if it, too, has three molts. _Lepus townsendii_ certainly has at least two molts per year.

KEY TO FAMILIES AND GENERA OF LAGOMORPHA

1. Hind legs scarcely larger than forelegs; hind foot less than 40; nasals widest anteriorly; no supraorbital process on frontal; five cheek teeth on each side above Family Ochotonidae, Genus _Ochotona_, p. 125

1'. Hind legs notably larger than forelegs; hind foot more than 40; nasals widest posteriorly; supraorbital process on frontal; six cheek teeth on each side above Family Leporidae, p. 134

2. Interparietal fused with parietals (see fig. 49); hind foot usually more than 105 Genus _Lepus_, p. 170

2'. Interparietal not fused with parietals (see fig. 10); hind foot usually less than 105 Genera _Romerolagus_ and _Sylvilagus_, pp. 137, 138

Family OCHOTONIDAE--Pikas

Certain characters in which this family differs from the Leporidae (hares and rabbits) are: hind legs scarcely longer than forelegs; ears short, approximately as wide as high; no pos...o...b..tal process on frontal; rostrum slender; nasals widest anteriorly; maxilla not conspicuously fenestrated; jugal long and projecting far posteriorly to zygomatic arm of squamosal; no pubic symphysis; one less cheek-tooth above, the dental formula being i. 2/1, c. 0/0, p. 3/2, m. 2/3; second upper maxillary tooth unlike third in form; last lower molar simple (not double) or absent (in the extinct genus _Oreolagus_); cutting edge of first upper incisor V-shaped; mental foramen situated under last lower molar.

Genus OCHOTONA Link--Pikas

Revised by A. H. Howell, N. Amer. Fauna, 47:1-57, August 21, 1924.

1795. _Ochotona_ Link, Beytrage zur Naturgesch, I (pt. 2):74. Type, _Lepus ogotona_ Pallas.

_Characters_.--Five teeth (excluding incisor) in lower jaw; first cheek-tooth (p3) with more than one re-entrant angle; columns of lower molars angular internally; transverse width of any one column of a lower molariform tooth more than double the width of the neck connecting it to the other column.

Subgenus PIKA Lacepede

1799. _Pika_ Lacepede, Tableau des Divisions &c., Mamm., p. 9. Type, _Lepus alpinus_ Pallas.

1904. _Pika_, Lyon, Smiths. Misc. Coll., 45:438, June 15.

_Characters._--Skull flattened; interorbital region wide; maxillary orifice roundly triangular; palatal foramina separate from anterior palatine foramina.

All of the living members of the family Ochotonidae belong to this genus. American pikas all belong to the subgenus _Pika_, which occurs also in Eurasia.

The distribution is boreal and the animals live in talus. This broken rock at the foot of a cliff provides interstices in which the animals live and store gra.s.s and herbs. These plant materials are cut for food and stacked in piles to dry in the sun, often beneath slabs of rock which protect the hay-piles from rain. Pikas are diurnal, active throughout the year, and have a characteristic call, "chickck-chickck."

Young number two to five per litter.

[Ill.u.s.tration: FIGS. 1-4. _Ochotona princeps tutelata_, Greenmonster Canyon, 8150 feet, No. 38519 MVZ, ?, 1.]

KEY TO NOMINAL SPECIES OF OCHOTONA

1. North of 58 N lat.i.tude; underparts creamy white, without buffy wash; an indistinct grayish "collar" on shoulders _collaris_, p. 126

1'. South of 58 N lat.i.tude; underparts washed with buff; no grayish "collar" on shoulders _princeps_, p. 127

=Ochotona collaris= (Nelson)

Collared Pika

1893. _Lagomys collaris_ Nelson, Proc. Biol. Soc. Washington, 8:117, December 21, type from near head of Tanana River, Alaska.