WESTERN CHIPPING SPARROW. Spizella passerina arizonae Coues

Field characters.—Decidedly smaller than Junco, and with narrower tail. Crown of head chiefly bright reddish brown (pl. 8d); stripe over eye ashy white; upper surface of body brown, with black streaks on back; under surface of body ashy white, unmarked in adults, streaked in juveniles. No white on tail. Voice: Song of male a monotonous cicada-like buzz, lasting several seconds; both sexes utter a weak tseet.

Occurrence.—Summer visitant widely from floor of San Joaquin Valley to near timber line on Sierra Nevada; found in nesting season from Snelling east to Tioga Pass. Most abundant in Transition Zone and least numerous in Lower Sonoran and Hudsonian zones. Passes through Mono Lake country during spring migration. Winters in small numbers at Snelling. Frequents various situations, most often margins of clearings adjacent to small trees. Forages chiefly on ground. Flocks loosely after nesting.

The Western Chipping Sparrow possesses special characteristics which serve to bring it quickly to the notice of anyone who goes camping in the Sierras. Smaller even than a junco, and marked by neither brilliancy of coloration nor attractiveness of song, it might easily be overlooked. But it has the regular habit of coming close about a camp site and hopping, with many quick movements of both head and body, and with seeming fearlessness, over the open ground. It thus chooses as its own forage area the same sort of place that the vacationist selects for his camp; and so the bird happens to come much more than halfway toward bringing about an early acquaintanceship.

As regards coloration, the Western Chipping Sparrow is more easily distinguished by lack of conspicuous features than by the possession of any positive color marks. Only one, the reddish brown crown patch (pl. 8d), stands forth with any prominence; otherwise, the adult bird shows ashy white, unstreaked lower surface, dull brown wings and tail, and inconspicuously streaked back. Young birds, up to two months or so of age, are narrowly streaked on the under surface as well as above. With the first autumnal molt they become plain on the lower surface, while the crown patch (pl. 8g) does not appear until the first pre-nuptial molt, the following spring.

The Brewer Sparrow which summers in the sagebrush east of the mountains is much like the chipping sparrow but never has the bright brown crown patch. The Black-chinned Sparrow of the foothill chaparral has a black chin and blue-gray head and hind neck. During the summer season the bill of the chipping sparrow is black or nearly so, but in other seasons it is light-colored. In neither of the two other species named does the bill ever become black.

An interesting instance of adventitious coloration was met with at Dudley, on Smith Creek, on July 11, 1920. An adult female chipping sparrow was captured which had the plumage of the whole under surface of the body strongly tinged with a pinkish color. This was doubtless due to a 'dust bath' that the bird had taken in the roadway a mile or so up the valley where the soil is predominatingly reddish in color.

Western Chipping Sparrows are notably active, ever moving rapidly about from place to place. They seek much of their food on the top of the ground in open spots under trees, and they must needs hunt for it over a considerable area rather than dig it out in one place; their claws are relatively small and weak as compared with those of the ground-scratchers, like towhees and fox sparrows. Their activity seems never at an end, for they are as busy in the heat of midday as in the chill of morning or cool of evening.

The notes of the chipping sparrow are very simple. Both sexes utter a single short weak tseet, while the song of the male is nothing more than a cicada-like trill or buzz, monotonous to a degree, and strongly sustained throughout. It lasts several seconds (2 to 9 in instances timed by us) and is repeated over and over again at short intervals.

The Western Chipping Sparrow is one of the most notable of our passerine species in respect to the wide range of its occurrence. Indeed, it is exceptional for the great diversity of climatic conditions under which it thrives in the Yosemite section, this being, also, an index to its great degree of hardihood. Some individual birds nest in the hot, dry, almost parched San Joaquin Valley, where the temperature in summer is often 100° F.; and others rear their broods about the cool snow-covered alpine meadows almost at timber line. Yet, within these extreme life zones, as well as through all the intervening territory, it is associated with a type of habitat or niche which upon analysis is seen to recur with corresponding regularity. This niche is the one in which small trees dot open expanses of smooth, relatively dry ground, either practically bare, or grassy. Such an 'association' is illustrated by an orchard at Snelling, by a blue oak hillside at Pleasant Valley, by a tract of young yellow pines adjacent to a meadow in Yosemite Valley, or by a stand of smallish lodgepole pines on the edge of Tuolumne Meadows. In other words, the Chipping Sparrow is to be found in almost any climate, providing its special associational needs are met. Here is a case, then, where character of habitat (niche) weighs more in the economy of existence than do the factors of climate.

The chipping sparrow population is not uniform throughout its wide range but varies in the different zones. The birds are perhaps most numerous in the Transition Zone and least common in the Lower Sonoran and Hudsonian zones. A continuous census along the Tioga road between Porcupine Flat and Snow Flat, on June 28, 1915, revealed one or two birds an hour. About this same number an hour was noted in the Upper Sonoran Zone at Pleasant Valley in May, 1915. In the Transition Zone, in Yosemite Valley, the average was six or more, seen or heard, in an hour's census.

The Western Chipping Sparrow arrives in the Yosemite section in April or May, and leaves by late September or early October (the 7th in 1920 [C. W. Michael, MS]). A few winter at Snelling where one was collected January 9, 1915, from a flock of about 20 in company with some Sierra Juncos. But the host which fills the foothills and mountains in summer-time spends the winter somewhere to the southward, either on the deserts of southeastern California or beyond, on the tablelands of Mexico. The birds arrive in April, as nest building was already in progress in Yosemite Valley on April 30 (1916); and individuals were well established in the foothills between Lagrange and Coulterville on May 9 (1919). Occupation of the higher mountains seems to be accomplished with little if any delay. By May 24 (1919) the species was well established at Tamarack Flat (altitude 6400 feet). Near Mono Lake on May 6 (1916) chipping sparrows were passing in migration, but they were not found there later that season. The return migration sets in during September, and by the end of that month most of the birds have gone. The last to be reported in Yosemite Valley were seen on September 29 (1917) (Mailliard, 1918, p. 16). Our latest record for any point above the level of the San Joaquin Valley is for October 7 (1914), when a few were noted at El Portal.

But little time elapses after their arrival in the spring before the chipping sparrows settle down to nesting duties; yet not all the birds complete the rearing of their broods at an early date. Pairs engaged in caring for eggs or young are apt to be found at almost any time up until early July. Our earliest record of nest building is for April 30 (1916), and the latest, of young still in the nest, was made on July 15 (1920). Probably the bulk of the birds in the Transition Zone and above begin nesting between the middle of May and the middle of June. At the higher altitudes, nesting comes later, probably because, due to the persistence of a low temperature there to a later date in the spring, sufficient food is not available earlier. But the discrepancy from this cause is not so great as might be supposed. At the lower levels the chipping sparrows nest after the first burst of bloom from the herbaceous plants is over, whereas around the high mountain meadows the birds have their nesting already well under way when the alpine flowers have only begun to appear. Thus, to a certain degree, the spring calendar for the birds is different from that for the flowers. The birds maintain their own body temperature in spite of the prevalent conditions about them, and may therefore be controlled more directly by other factors, such as that of available supply of food.

At El Portal on the morning of April 27, 1916, a male chipping sparrow was seen in courting display before a female. He uttered notes sharper than the usual ones, more like the syllable tsa, uttered singly or trilled in series. As the notes were given, each was accompanied by a slight shrug of the body and downward movement of the tall. The two birds passed back and forth, hopping and flying, amid red-bud, buckeye, and live oaks.

A majority of the nests of this bird are placed between 4 and 6 feet from the ground; very few are more than 12 feet up. The lowest nest found by us in the Yosemite section was only 2 feet above the ground and the highest approximately 16 feet. Almost any sort of tree or large bush is used for a site. In a bush or small tree the nest is most often placed near or at the top; while in a large tree it is situated near the end of a lower outreaching branch. We saw nests in blue oak, live oak, incense cedar, yellow pine, lodgepole pine, and orchard trees, as well as in deer brush and wild rose, and once in a cultivated blackberry vine.

The nests of the Western Chipping Sparrow are of such an unique type that they may be readily identified without the necessity of seeing the makers. No other bird of the Yosemite region builds a nest of the same form or constituency. The foundation is of long fine weathered stems of grasses and other plants, so laid together and interlaced that they constitute a firm yet porous structure not easily shaken to pieces. Internally, the nest proper is of a deep cup-shape, walled with a neatly woven layer consisting solely of long mammal hairs, wound about so as to produce a perfectly smooth interior surface. This inner lining is so well woven that it can be lifted free of the foundation part of the nest and still retain its shape, almost like a piece of hair cloth. This type of nest seems well adapted to the kind of site preferred by the chipping sparrow, namely, the outer loose foliage of trees, upon a large area of which the nest platform can rest without danger of disintegration or of falling from place. The nest cavity measures in ascertained cases 1-7/8 inches in diameter by 1-1/4 inches deep. Externally there is naturally much variation in dimension; one nest measured in place was 3-1/4 inches in diameter and 2-1/4 inches high.

Four is the usual number of eggs laid; none of the nests seen by us held more. Several nests held only 3 to 2 eggs or young, but in these cases there is the possibility that some of the clutch or brood had been lost.

During the nesting season chipping sparrows are as fearless as at other times. The observer can often approach very close to a nest before the sitting bird will leave. We have set up our camera, unscreened, within two feet of a nest, and the female remained on the nest during most or all of the manipulations incident to the taking of a picture.

After the broods are reared, parents and young join in family parties and wander about in their daily quest for food. Sometimes several of these groups gather in a loose flock of a score or more. After the late-summer molt, there is no renewal of the song, as with some sparrows; only the weak call notes are given. In early autumn the "chippies" quietly take their leave, and by the first week in October the observer finds the species no more among the birds recorded in his daily census.