CALIFORNIA GULL. Larus californicus Lawrence

Field characters.—A gull of medium size; total length 20 inches or more. Plumage of adults (pl. 41a) white on whole head, neck, lower surface and tail; back neutral gray; wings black-ended, with white spots near tips; bill yellow, with dark band near tip and an orange spot near end of lower mandible. Plumage of immatures mixed dark and light brown. Wings long and pointed, tail short and square-ended; flies gracefully, frequently sailing or circling on set wings; when on water sits high, with tips of wings crossed behind back.

Occurrence.—Common in summer on Mono Lake, nesting on Paoha Island; occasionally straggles over Sierran crest to lakes on west slope; noted at Tuolumne Meadows (8600 feet), July 5, 1915, at Young Lake, altitude 10,000 feet, July 8, 1915, and at Tenaya Lake, altitude 8141 feet, July 29 and September 26, 1915.

Most people associate gulls with the seashore. This disposition in general is correct in so far as the winter season is concerned, but during the summer months several of the species leave their maritime haunts altogether and seek bodies of water far inland. Such is the case with the California Gull.

In 1915 we saw California Gulls only four times, as detailed above; but in the late spring and early summer of 1916, when Mr. Dixon visited Mono Lake, he found them there in numbers. On May 6 three birds were seen at the mouth of Leevining Creek; by the latter part of the same month the species had become common there.

On May 27, 1916, Mr. Dixon visited the nesting colony of California Gulls on Paoha Island, the larger of the two islands in Mono Lake. (See pl. 41.) From the north side of Paoha two ridges of black obsidian-like rock extend northward about 200 yards out into the lake. These ridges are about 20 feet high and enclose a long narrow bay about 10 or 15 yards wide and 100 yards in length. Gulls nest on both of these peninsulas but chiefly on the eastern one which bears a rather dense growth of a shrubby plant. Here, over an area of 1-1/2 to 2 acres, there was an average of at least one nest for every 100 square feet; in some places it was estimated that there was one to each 10 square feet. The total number of breeding birds was believed to be close to 1000 pairs.

The nests were placed on the rocky shingle of the beach, in depressions under bushes and on the tops of rocks. Nesting material was scanty, consisting chiefly of old wing feathers, molted in previous years. Many mummified bodies of half-grown young of last year's brood were lying about, and in one instance one of these mummies formed the principal part of the nest. Nests containing 2 eggs were more common than those with one or with 3 eggs, the latter occurring in about equal numbers. One nest held 4 eggs, but this large number was clearly the result of two birds laying in the same nest; for 2 of the eggs were relatively short with a light greenish ground color, while the other 2 were longer, more pointed, and of a brownish ground color. Laying had evidently commenced about May 15, for many of the eggs contained half-developed embryos, but none had yet hatched. The parent gulls seemed to appreciate the need for sheltering their eggs from the intense heat of the sun, which beat down on the bare black rocks. They were often seen standing so as to cast a shadow over their eggs, while they themselves held their mouths open and panted from the heat. Males were seen whose actions seemed to show them to be urging their mates to return to the nests; in some instances they accompanied the females when the latter returned to their duties.

On July 3 a second visit was made to the Paoha Island colony. By this time practically all of the eggs had hatched; about one-third of the young were running about, well feathered and almost half grown. Four nests were found with chicks not more than a day old, and one contained a downy gull so recently hatched from the egg that it was not yet dry. Despite its recent emergence from the shell, this chick was able to scramble about until it found shelter in the shade of a rock. Apparently the adult birds had been more successful with their broods this year, for there were few dead bodies of young gulls about and no infertile eggs. It is possible, however, that abandoned or infertile eggs are promptly eaten by neighboring members of the colony.

In one part of the colony there are many hop-sage bushes about 3 feet high and 3 or 4 feet in diameter. These grow close to the ground, and the strong wind which continually sweeps the island blows the molted white body feathers of the parent gulls against these bushes until each bush has at its base a feathery white windrow often six inches thick. When alarmed, the gray downy young gulls rush headlong into these windrows and do not stop until they are entirely hidden. The larger young, in dusky juvenal plumage, are not so fortunate. They cannot hide their whole bodies in the windrows, and their stubby black tails remain projecting out beyond the drifted feathers in a very grotesque manner. Six youngsters were pulled out of one windrow and there were still other, smaller chicks hidden in the mass. Holes in the rocks were also favorite shelters and places of concealment for the small young; often a chick would shade its head in a small cavity while its body remained out in the broiling heat of the sun.

When disturbed, the larger young headed for the beach, jumping and tumbling over the rocks faster than a man could walk. When they reached the ten-foot bank which borders the waters of the lake they did not hesitate, but plunged over the edge. Once in the water they seemed perfectly at home and swam about, 100 yards offshore, where they were herded into 'rafts' by the parents and prevented from going farther out. (See pl. 41c). As soon as the intruder retired, the young turned back toward the beach. Once, when a party of a dozen juvenile gulls started down the slope toward the water, they loosened a veritable avalanche of small rocks. Gulls and rocks were pretty well mixed by the time the water was reached and it seemed as though some of the birds would certainly be killed; but they all swam away apparently unharmed.

The young gulls when first hatched eat bits of eggshell, but soon their diet consists exclusively of brine shrimps. Birds 3 or 4 days old had, we found, a considerable number of these crustaceans in their stomachs. When handled, the first thing a young gull does is to throw up quantities of brine shrimps; and the adults, flying overhead, show their displeasure at the disturbance of the young by pouring down similar disgorgements. When undisturbed the adults stand on guard at the nest site. The young play around in the vicinity, but seem always to return to the nest site for feeding. The larger young frequently climb up on the tops of the rocks to await the return of the parents.

The old birds often visit fresh-water lakes in the vicinity to feed on the huge frog tadpoles which there abound. An adult bird captured near Williams Butte on June 23, 1916, disgorged several of these large tadpoles.