Natural History of the Ground Squirrels of California/Catalina Island Ground Squirrel
CATALINA ISLAND GROUND SQUIRREL.
Citellus beecheyi nesioticus Elliot.
Other names.—Island Spermophile; Citellus nesioticus; Spermophilus beecheyi, part.
Field characters.—As for the Beechey Ground Squirrel. Only to be distinguished from it on comparison of series of specimens; coloration averaging darker, general size greater, and tail relatively shorter. Length of body alone, in males, about 11¼ inches; with tail (without hairs) about 7½ inches more.
Description.—Adults in April: Similar to the Beechey Ground Squirrel (San Francisco Bay region) as already described, but general coloration darker; top of head from nose to nape, and broad area down middle of fore back between light shoulder patches, deep cinnamon-brown, the hairs individually being black, tipped with cinnamon; middle of back darker in tone than top of head; spot above upper eyelid blackish; cheeks and sides of neck much darker in tone than in beecheyi; whitish shoulder patches, restricted in extent, dull and indistinct as compared with fisheri and douglasii, even more so than in beeclieyi. Under surface of body very dark in tone, the hairs extensively grayish bister at bases and tipped with cinnamon buff. Tail and feet colored as in beecheyi.
Color variations.—The type and one other specimen show a black patch on the crown, due to lack of cinnamon hair-tippings; this, of course, is merely an individual feature.
The May-taken series at hand shows various transition stages from winter to summer pelage. In most of the specimens the fore parts are in fresh harsh summer coat, while the rump is still covered with the winter coat, showing underfur, and being more or less worn and faded. The tail in some examples is markedly worn and faded, with the usually resulting changes in color. In some specimens the hairs of the tail show but two dark bands instead of three; but this variation occurs also in other near-related races of ground squirrels. The two skins taken in February are in full winter pelage, showing more or less underfur over the whole body and no signs of molt. The fore parts, as compared with the summer pelage, are less bright in color tones, and the shoulder patches are even less distinctly whitish. Hinder upper surface and tail exactly as in beecheyi of same season.
Measurements.—Average and extreme measurements, in millimeters, of nineteen full-grown specimens from near Avalon, Catalina Island, are as follows: Seven males: total length, 471 (447–495); tail vertebræ, 189 (175–200); hind foot, 59 (55–63); greatest length of skull, 60.2 (56.1–63.7); zygomatic breadth, 36.9 (33.8–39.2); interorbital width, 14.8 (13.3–15.9). Twelve females: total length, 444 (406–475); tail vertebræ, 179 (161–194); hind foot, 56 (53–62); greatest length of skull, 57.7 (54.0–62.4); zygomatic breadth, 35.9 (33.3–37.6); interorbital width, 14.3 (13.0–15.4).
Close examination of the series of skulls shows to us no character by which to tell them from beecheyi or fisheri except for average greater size. There is the usual range of variation in proportions, due to age, this factor being judged from degree of wear on the crowns of the molariform teeth. Old skulls are largest, broadest relatively to length, and with most prominent ridges and processes. It is difficult for us to understand how Elliot (1904, p. 263) could have assigned the numerous cranial characters he did to the form he named, except on the ground that he examined but a very few specimens of beecheyi and fisheri and that these happened to be extreme.
Type locality.—Santa Catalina Island, California (Elliot, 1904, p. 263); more exactly, vicinity of Avalon, according to the collector of the type, Mr. John Rowley, in interview.
Distribution area.—Santa Catalina Island, California. Life-zone, Upper Sonoran.
Specimens examined.—A total of 21 skins and skulls, all from the vicinity of Avalon, Catalina Island. Two of these (including the type) were loaned us from the Field Museum of Natural History, Chicago; and nineteen were loaned us from the Museum of History, Science and Art, Los Angeles.
Only three species of rodents are known to be native to Catalina Island, a harvest mouse, a white-footed mouse, and the Catalina Island Ground Squirrel. This last-named animal is, as in each of the other cases, but slightly differentiated from its counterpart on the adjacent mainland. With little doubt it differs no more from its near relative, the Beechey Ground Squirrel, in general habits and traits, than it does in structure.
Until the present year very little has been known of the Catalina Island Ground Squirrel. In fact, the original characterization of the race was so unsatisfactory as to leave doubts in the minds of some students as to whether the island animals really differ at all from the mainland ones. Fortunately for the present writers, our appeal to Mr. Frank S. Daggett, Director of the Museum of History, Science and Art, in Los Angeles, was promptly met by action, and Mr. L. E. Wyman of Mr. Daggett's staff was detailed to go to Catalina and obtain a sufficient number of specimens for deciding the doubtful questions. Mr. Wyman was eminently successful, and the resulting series of skins and skulls, together with the accompanying information, was freely placed at our disposal for use in connection with the present paper.
Mr. Wyman found the squirrels fairly swarming May 9 to 16, 1918, at the upper end of a narrow tract of bottom land about a mile back of Avalon. This tract, dotted with elderberry trees, had been seeded to barley, and the grain stood knee-deep except in the spots where it had been persistently eaten down by the squirrels. The hillside adjoining on the northwest was steep and fairly well covered with cactus and chaparral, and in places it was honeycombed with burrows. The bottom of the hill was beset with extensive diggings every fifty feet or so.
Besides the barley, the squirrels were feeding on a variety of wild vegetation. Each of the numerous stomachs examined contained a well-chewed green mass. Cheek-pouches were found to contain barley blades and certain seeds, and in one case four bulbs of "sour-grass" or "grass-nuts" (Brodiæa capitata), the largest of which was half an inch in greatest diameter. These bulbs seem to be specially sought after, as several small areas were found, usually on south-fronting grassy hill-sides, where the ground was all dug up by the animals, and hulls of Brodiæa bulbs were lying about.
One ground squirrel was seen at work in a wild tobacco tree about seven feet from the ground. He had gnawed at the stem near the top until only a shred kept it from dropping. Gnawed shells of chilicothe seeds were also found.
Mr. Wyman believes that the notes and actions of the Catalina Island Ground Squirrel do not differ to any appreciable extent from those of the mainland Beechey. The island animals were perhaps slightly less noisy, though when once started to barking they seemed hardly able to stop. They were found to be shy on open ground, hustling to cover when the invader of their domain was yet 200 yards off. By sitting quietly under a tree, however, Mr. Wyman had one squirrel approach him to within ten yards and feed on barley shoots. On the brushy hillsides, the collector was able to stalk his quarry with ease.
All the females taken were notably fat, and none contained embryos. Also no young of the year were seen; so that it would seem that the breeding season of the island squirrel is much later than that of the mainland animal—later, at least, than May 16. Every specimen taken by Mr. Wyman was "loaded with fleas;" these, however, quickly disappeared and in no case caused any annoyance to the collector.
Since ground squirrels were seen by the senior author commonly in August, 1903, in the vicinity of the Isthmus, near the northwest end of Catalina, it may be inferred that the animals are widely distributed over this island. No species of ground squirrel whatever exists native on any of the other California islands.