SIERRA CROSSBILL. Loxia curvirostra bendirei Ridgway

Field characters.—Somewhat larger than Junco but of more chunky build. Head large appearing; tail small, short, and decidedly notched at end. Bill heavy, mandibles much curved, and crossed near end (whence the common name). (See fig. 51.) Body plumage dark gray, variously tinged with greenish, orange or red (see below). Flight undulating, goldfinch-like. Voice: Call notes, sup or chup, usually uttered in three's, and most often given as the birds take wing or fly from place to place.

Occurrence.—Moderately common resident in the Boreal region (Upper Transition, Canadian, and Hudsonian zones) on both slopes of Sierra Nevada. Observed at several stations, from Hazel Green east to Mono Mills. Also reported to visit Smith Creek, 6 miles east of Coulterville, in fall and spring (D. D. McLean). Frequents cone-bearing trees usually far above ground; occasionally forages on ground. Seen by us in small parties of a dozen or less, sometimes in company with other finches.

The Sierra Crossbill is the local representative of a species which is found throughout the more boreal parts of the northern hemisphere. In our latitude in summer it is an inhabitant of the mountains, and it quite likely remains there through the winter as well, though flocks may some years descend in the latter season to the foothills and valleys. It is impossible to predict with certainty concerning its appearance at any one time in a particular locality; for its local occurrence varies with the changes in food conditions. Nor, as regards the Yosemite region, can any definite information be given relative to the time or place of its nesting.

The Sierra Crossbill is likely to be encountered at one time or another at almost any place in the upper part of the Yosemite region. Our first definite record of the occurrence of the species came on September 28, 1915, when three of the birds were seen on Tuolumne Meadows. Others were noted at the same place on September 29, and near Glen Aulin on the latter date. Four were seen near Mono Mills on June 10, 1916. At Hazel Green on May 14 and 15, 1919, the species was relatively common, and it was noted once near Tamarack Flat, on May 24, 1919. On each of the dates mentioned the birds came to notice at close range and appeared to be relatively unwary. The irregularity of their observance must be attributed not to shyness, but, first, to their habit of foraging high above the ground, near the summits of lofty trees, where their presence may be altogether unsuspected, and second, to their propensity for wandering.

The plumage of the male crossbill, as exhibited by a series of specimens, shows much variation in coloration. It is generally assumed that as the birds increase in age they acquire, at successive molts, more and more red in the coloration; but this supposition remains to be proved. Male birds, which by dissection are shown to be in breeding condition and hence mature in the generally accepted sense of the word, exhibit a wide range of coloration, from greenish yellow through orange to brilliant red. The bright color is distributed rather generally over the under surface of the body, and on the head and rump. It is least in evidence on the back and practically absent on the wings and tail. Females are different in color from most males, in that they retain the gray plumage, tinged with greenish or at most with a suggestion of yellow, throughout life. The young of both sexes are streaked on the under surface of the body, looking at this time much like the female of a California Purple Finch.

At Tuolumne Meadows on September 28, 1915, three crossbills came to the seepage area within 75 feet of the log hut which protected the main outlet of the soda springs. The birds seemed to drink, stayed a few minutes, and then flew to a lodgepole pine close to the Sierra Club lodge. There they set to work on the new cones, hanging head downward as they worked at the ends of the terminal twigs. They gave an occasional chirp, and when one of the birds started to fly this note was repeated often in couplets, chip-chip, chip-chip, chip-chip, reminding one of the chirps given by linnets under similar circumstances. The flight, too, was suggestive of that of the latter bird. One of these crossbills was a male in the red livery, whereas the other two were evidently females. Later, the birds descended to the ground and foraged among the fallen debris. Another small assemblage composed of a red male, an orange-colored male, and two supposed females, was seen momentarily at Mono Mills on June 10, 1916, as they came to drink at a tub near a water tank. On this occasion the observer remarked upon the resemblance of the birds in voice and flight to goldfinches.

Fig. 51. Bill of Sierra Crossbill, from (a) side and (b) above; and (c) cone and (d) seeds of lodgepole pine; all natural size. The twisted mandibles enable the bird easily to spread the scales of the pine cone and to obtain the seeds thus released.

At Hazel Green a mixed flock of finches, comprising 8 or 10 Sierra Crossbills, about half a dozen California Evening Grosbeaks, and about a dozen Cassin Purple Finches, was seen industriously foraging in the chaff at the side of an old stage barn early on the morning of May 14, 1919. This assemblage seemed to stay together for the morning meal, but broke up as the day progressed. By hiding inside the barn the observer was able to get within a yard of the birds without arousing their fear and so to watch closely their movements. The crossbills seemed to take the preferred positions and were less wary than the other two species. When hunting in the chaff, the crossbills used their pinkish tongues repeatedly and opened their bills wider than the other finches, probably because of the peculiar form of their mandibles. When taking flight the birds separated into pairs, although as stated elsewhere it was not likely that they were nesting at the time.

These crossbills usually uttered their notes when in flight or when just about to take flight. The notes were uttered in chains of three, with diminishing emphasis toward the end, chup', chup', chup; chup', chup', chup. In flight the notes were given in unison with their aerial swings, as are the flight notes of the Willow Goldfinch. While feeding, either on the ground or in the terminal foliage of the lofty trees, the crossbills were silent.

The usual forage niche of the Sierra Crossbill is in the tops of coniferous trees where the bird obtains the seeds from the ripening cones. In extracting these seeds the peculiarly crossed mandibles are believed to be especially helpful, for by their use a bird, in turning its head, gets a double leverage to separate the scales of the cone. (See fig. 51.) Some of the crossbills subsistence is gained on the ground. Like the purple finches, they do not forage in, or frequent, intermediate situations such as brush patches. One of the birds at Tuolumne Meadows, upon being collected, was found to have its throat crammed with seeds of the lodgepole pine; the birds at Hazel Green were getting a variety of seeds and grain from the barnyard litter.

We found no direct evidence of nesting on the part of the crossbills which we saw or collected, nor were any young in the streaked juvenal plumage observed. The skin of the abdomen of a female collected at Hazel Green on May 14, 1919, was bare and wrinkled, and rather leathery in texture, as if it had been glandular. Its condition was that to be expected in a bird which had been incubating perhaps two months previously.