FOX SPARROWS. Passerella iliaca (Merrem)³¹

Field characters.—Of chunky build, between Robin and Junco in size. Upper surface almost uniform dark brown, grayish, or reddish in tone, according to subspecies; wings and tail in any case with more or less of a foxy red tinge; under surface white, with bold triangular spots of dark brown or grayish brown, most numerous on fore neck (pl. 48a); no white markings on either wings or tail; bill varyingly stout, dark-colored, in some races yellow below at base. Voice: Of both sexes, a loud sharp single call note, clink; song of male notably clear and melodious in quality.

Occurrence.—Common in summer in Canadian Zone on both slopes of Sierra Nevada, ranging down to 5500 feet altitude, as near Chinquapin, and up to more than 8000 feet, as at Porcupine Flat. Also, in different subspecific forms, a migrant and winter visitant, rare in Lower Sonoran Zone, but common in Upper Sonoran and (except during periods of heavy snows) Transition zones, throughout the region. Inhabits thick brush, under which it industriously forages with much sound of scratching in the dry litter; found singly or in pairs, never in flocks.

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³¹The eight subspecies of Fox Sparrow which occur in the Yosemite region differ in varying degree from one another in one or more characters. Some of these minor points of discrimination cannot be seen except by close examination of specimens in hand, but others are determinable even in the field. For example, even a novice, remaining in the region throughout the year, could recognize the differences between the gray backed birds of summer with big bills (mariposae and monoensis) and the brown-backed subspecies of winter with medium-sized or small bills (unalaschcensis, sinuosa, insularis, and altivagans). Schistacea is a gray-backed winter visitor with very small bill. Megarhyncha is gray-backed, with large but relatively short bill, and of rare occurrence in early winter. Such data as we have do not show any regularity or restriction in the occurrence of these different wintering subspecies. Probably all of them could be recorded in any one of a number of localities on the west slope, were collecting extended over a sufficient period of time.

The names and ranges of the birds occurring in the region at different seasons of the year are given in the following paragraphs. For the criteria of discrimination between these races we must refer the reader to the detailed account of the Fox Sparrows given elsewhere by Swarth (Univ. Calif. Publ. Zool., 21, 1920, pp. 75-224, pls. 4-7, 30 figs. in text).

SHUMAGIN FOX SPARROW, Passerella iliaca unalaschcensis (Gmelin), winter visitant to west slope of Sierra Nevada; found by us from Snelling (250 feet altitude) to Yosemite Creek (at 7800 feet). Earliest record, at latter locality, October 6, 1915. Summers on Alaska Peninsula and nearby islands.

KADIAK FOX SPARROW, Passerella iliaca insularis Ridgway, winter visitant to west slope of Sierra Nevada; found by us from El Portal (2000 feet) to near top of Yosemite Falls (6500 feet). Earliest record, October 14 (1915), from Aspen Valley (6400 feet). Summers on Kadiak Island, Alaska.

VALDEZ FOX SPARROW, Passerella iliaca sinuosa Grinnell, winter visitant to west slope, from Lagrange (300 feet) to Aspen Valley (6400 feet). Earliest record, October 14, 1915, from latter locality. Summers in vicinity of Prince William Sound, Alaska.

ALBERTA FOX SPARROW, Passerella iliaca altivagans Riley, late winter visitant: near El Portal (at 3800 feet), December 15, 1914; Pleasant Valley, December 4, 1915; six miles east of Coulterville, December 25, 1918, and January 20 and 27, 1919; Aspen Valley (6400 feet), October 14, 1915. Summers on Canadian Rockies along boundary between Alberta and British Columbia.

SLATE-COLORED FOX SPARROW, Passerella iliaca schistacea Baird, winter visitant to both slopes of Sierra Nevada, from Pleasant Valley (600 feet) to Warren Fork of Leevining Creek (at 9200 feet). Earliest record, September 13, 1915, at Gem Lake (9036 feet). Only migrant species observed on east slope. Summers in Great Basin and included mountain ranges from British Columbia south to Colorado.

MARIPOSA FOX SPARROW, Passerella iliaca mariposae Swarth, summers in Canadian Zone on west slope of Sierra Nevada, from Hazel Green (5600 feet) to near Porcupine Flat (at 8100 feet) and Washburn Lake (at 7800 feet). The majority depart about October 1. One apparently wintering individual captured six miles east of Coulterville, January 20, 1919. Winters chiefly in southern California.

MONO FOX SPARROW, Passerella iliaca monoensis Grinnell and Storer, summers in Canadian Zone on east slope of Sierra Nevada, as at Mono Lake Post Office (6500 feet), Walker Lake (8000 feet), and on Parker Creek (at 7500 and 8600 feet). Earliest spring record May 9, 1916, at Walker Lake; last fall occurrence recorded, September 11, 1915, at same station. A specimen taken on the Tuolumne River at 6300 feet, October 1, 1915, was probably a transient. Found in winter six miles east of Coulterville, December 25, 1918, and January 20 and 27, 1919.

THICK-BILLED FOX SPARROW, Passerella iliaca megarhyncha Baird, rare winter visitant to west slope of Sierra Nevada. One instance of occurrence: El Portal (2000 feet), November 28, 1914. Summer range not yet known.

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When the summer traveler in the Yosemite region reaches the Canadian Zone, with its thickets of huckleberry oak, chinquapin, and snow bush, he encounters the conspicuously distinctive inhabitant of this zone, the Fox Sparrow. It is true that the Green-tailed Towhee inhabits practically the same territory, but here the Fox Sparrow is the predominant species, outnumbering this towhee fully three to one.

The Fox Sparrow is a sprightly bird of trim and pleasing appearance, easily recognized by its distinctive coloration, as described above. Its upper surface entirely lacks any contrasted markings, but the under surface of its body is white, strikingly patterned with large triangular spots of dark brown. (See pl. 48a). These spots have their apexes pointed upward, and on the lower part of the throat they are massed together forming a more or less distinct patch. No other sparrow in the region possesses this combination of uniform upper surface and patterned under parts. The Song Sparrows have streaked upper surfaces and are also considerably smaller in size. The Hermit Thrush is similar in general coloration to the Fox Sparrow, but differs in its slender bill, big-eyed expression of face, and, most emphatically, in mannerisms and voice.

The fox sparrows are essentially birds of the brush, and they rarely venture far into the open. In late spring and summer the males, when giving voice to their clear melodious songs, perch on the uppermost twig-tips of their favorite thickets, and occasionally even mount 30 or more feet to some bare branch in an adjacent coniferous tree. But at other seasons the males as well as the females are invariably of retiring disposition. They both always do their foraging under or near brush, and when pursued prefer to dive deeper into the home thicket rather than to fly off to another shelter as do Golden-crowned, White-crowned and Intermediate sparrows; if finally driven out they often circle about in erratic flight and return to the same thicket from which they were flushed. Often when an observer moves around trying to catch sight of one of the birds the latter will hop about, uttering its sharp clink, and manage to elude observation by keeping on the opposite side of the thicket or behind a tree trunk or branch. Their movements are mouse-like, but as they move about, one notes at close range an audible flutter of the wings such as characterizes so many other brush-inhabiting sparrows.

The fox sparrow forages exclusively on the ground, and does not even seek the berry crops which are commonly borne on bushes within but a few feet of the earth. It scratches persistently in foraging beneath the brush thickets, jumping up and kicking vigorously backward with both feet simultaneously. This procedure sends a small shower of leaves and loose earth back from where a bird is digging, and often shallow holes 2 or 3 inches in diameter are left as a result. The quantity of food material obtained evidently justifies the seemingly large amount of energy expended in the search, as the birds can be seen to stop frequently and glean titbits uncovered in their scratching. It is when absorbed in scratching under the bushes that the coloration of the fox sparrows serves best to conceal them from view; if the birds remain moderately quiet they fairly melt into the background of brown earth and dry leaves.

When perching these birds assume a peculiarly upright posture; but they seldom remain long in one location, and as they move about from twig to twig in the bushes, or on the ground, their strong legs and feet enable them to move with marked grace and precision. Although this sparrow is continually busy through most of the daylight hours, the twilight of evening and morning marks its period of greatest activity. In summer the males often leave their favorite haunts early in the morning and move uphill, even ascending to the summit of some conifer to catch the first rays of the coming sun, which they greet with full-toned songs. At Hazel Green on May 15, 1919, a male sang twice at 3:50 A.M., which was at the earliest peep of daylight.

The song of the male fox sparrow is among the most pleasing of the bird songs of the high mountains. The individual notes ring out strongly and clearly, the major ones being well enunciated. At Hazel Green on May 14, 1919, a singing bird was watched for a long time as he sat perched at the top of a 9-foot Douglas spruce. He was motionless, except when singing, and even after his song had been heard a number of times it required some search to determine his exact location among the many small trees in that particular glade. At intervals of from 8 to 20 seconds up would go his head, his bill would open, and forth would come the song, his entire body quivering with the effort of utterance. His songs were of two types, neither of which was satisfactorily expressible in writing. The number of syllables in each group of notes varied somewhat, but otherwise the songs differed only by occasional omission of a trill which was the conspicuous element in one of the types.

The male fox sparrow seems not to indulge in any elaborate courting behavior such as is characteristic of certain other birds. His song is evidently a sufficient demonstration. But at Chinquapin, on May 19, 1919, a singing male while perched had its tail widely spread. This habit is very common among the males of some birds during the spring months, but its use by the fox sparrow shows that it is not peculiar to species with white tail markings, in which the display is so much more conspicuous.

These birds are quite secretive as regards their nesting. In 1915, when necessary attention to many other species limited the time which could be devoted to fox sparrows, we did not find any occupied nests, and but one bob-tailed fledgling (fig. 55a) came to our attention. But in 1919 several nests were discovered, although only after a careful and continued search.

The first nest, located at Chinquapin on May 21, 1919, was scarcely 300 feet from the government barns on the stage road. It was situated on a small level bench covered with snow bush and chinquapin and close to a forest of firs and sugar pine on the slopes of Indian Creek. A male bad been noted there singing regularly at short intervals during the preceding two days. His song perch was about 6 feet above the ground and halfway up in a clump of small black oaks which were just coming into leaf. Occasionally he would go to another perch a few yards distant and above the chaparral; and more rarely he mounted 40 feet or even more above the ground to one of the dead lower branches of a nearby sugar pine. But fully four-fifths of his singing was done from the first mentioned perch, which was found to closely overlook the nest site 50 feet distant and due south. The female was usually out of sight.

Once both birds were observed together, the female feeding along the ground and frequently fluffing out her plumage as is the custom of an incubating bird. She uttered the Brown Towhee-like 'clink' note at short intervals. The male was in close attendance but not singing. Presently the female, followed by her mate, flew to the top of a patch of Ceanothus cordulatus about 25 feet in diameter, and after a look around, disappeared into the clump. The male thereupon repaired to his usual post and sang. After a minute or so the observer, who had been watching at some distance, went to the brush patch where the female had disappeared and shook one side of it, whereupon the female slipped through beneath the mat of the thicket and then hopped across the adjacent opening, unconcernedly picking here and there in the loose earth and debris. A moment's search revealed the nest, examination of which elicited no evident anxiety on the part of the female bird. The observer returned to the spot later and as he approached, the female slipped from the nest when he was only about 8 feet away. She was not seen again for some minutes; then she came within 15 or 20 feet giving the sharp call note. The male had meanwhile ceased to sing.

The nest was well concealed from above, although when once located it was easily seen from one side. It rested on a low dense tangled mat of Ceanothus twigs and foliage, both living and dead, about 6 feet in from the margin of the patch and 3 feet out from where a group of stems emerged from the ground at a common root center. There was a canopy of green Ceanothus leaves 150 millimeters above the nest, the rim of which was 240 millimeters above the surface of the ground. The basal portion of the structure was composed of short coarse twigs, not interlaced, and these fell apart when an attempt was made to lift the whole nest clear of the tangle. This basal portion was about 280 millimeters in diameter. Then came a layer of pine needles more closely laid, and finally the lining of the nest cavity, of deer hair (deer are particularly abundant at Chinquapin), together with a few long black mane or tail hairs of horses. The cavity measured 65 millimeters in diameter by 37 millimeters deep.

Four nests found near Tamarack Flat on May 25 and 26, 1919, were in various stages of construction and, in practically all respects, were identical with the nest just described. The heights of the nests above the ground were, respectively, 200, 380, 450, and 600 millimeters, and they were all in snow bushes.

The three fresh eggs which the Chinquapin nest contained were of very dark color, the ground tint of blue being heavily overlaid with brown marks which coalesced in many places and completely obscured the deeper-lying pigment. This heavy coloration is characteristic of fox sparrow eggs generally, as contrasted for instance with those of the Green-tailed Towhee inhabiting the same sort of country, which are notably light colored.

The contents of this nest indicated that nesting activities had begun some time during the first half of May. The fledgling bird referred to above was found near the same station, Chinquapin (at 5500 feet altitude), on June 13, 1915, which again would place the beginning of nesting near the middle of May. The season continues for some time, for birds at Tamarack Flat on May 25 and 26, 1919, had nests only in process of construction or barely completed, and other evidence which we have obtained points to a nesting season lasting until mid-July.

During the nesting season the birds are noisy and the males are belligerent, each jealously guarding his home precinct. A male watched at Mono Meadow, June 20, drove away in quick succession a Western Tanager and a Wright Flycatcher. On August 17, 1915, an adult and one juvenile fox sparrow were seen under some golden oak brush near Glacier Point. The adult seemed unusually forward in its actions as if it were attempting to distract attention from the young bird.

Up till late in the fall, as in summer, the thickets of the Canadian Zone, so long as they are free from snow, are inhabited by fox sparrows. The mannerisms of the birds then in evidence are the same as in summer and the same places are frequented—but the grayish brown birds of summer have been replaced by birds with reddish brown backs. The former, the Mariposa and Mono fox sparrows, have emigrated elsewhere, and from the north, from various places in Canada and Alaska (see footnote 31) have come several races of brown-backed birds. The replacement is complete and yet so gradual that the casual observer would not detect the exchange. These winter visitants from the north also take possession of the lower zones, the Lower Sonoran as at Snelling, Upper Sonoran as at El Portal, and Transition as in the western part of Yosemite Valley. We believe that in summer the temperature conditions in these lower zones are unsuited to the requirements of the fox sparrows, or else that the niche which they occupy there in the winter is in summer filled by other species. Then, too, fox sparrows, being ground-feeding birds, must live below the altitude at which snow lies on the ground for any length of time. Thus the brown-backed birds which migrate into the Canadian Zone in the fall drop to lower elevations when the heavy snows of winter come.