WESTERN ROBIN. Planesticus migratorius propinquus (Ridgway)

Field characters.—Size medium (length 10 inches); bill slender; tail nearly as long as body. Lower surface of body bright reddish brown; upper surface plain dark slate gray, blackish on head and tail; chin white; area under base of tail white. Young birds have under surface of body pale reddish and conspicuously marked with rounded black spots (fig. 60). When on ground moves rapidly, either walking or hopping; stops abruptly and fixedly in upright posture for a few seconds after each advance. Flight steady, not undulating. Voice: Of male, a loud caroling song. Both sexes utter short calls, some of them sounding like squeals; these given singly or in various combinations.

Occurrence.—Common summer visitant to forested portions of the Yosemite region from near Bullion Mountain, El Portal, and 3 miles east of Coulterville, eastward across the Sierra Nevada to Mono Lake Post Office; most abundant in Transition Zone on west slope, less numerous at the higher altitudes and on the east side of the mountains. Also common as a winter visitant in foothills of the west slope from El Portal and 6 miles east of Coulterville west to Pleasant Valley. A few remain in Transition Zone, as in Yosemite Valley, in certain winters. Forages chiefly on open grasslands in summer and generally in berry-producing trees and bushes in winter. Seeks open branches of trees for singing and roasting. In pairs or family groups during nesting season; in loose flocks up to 50 or more at other times of year.

The robin, of all our birds, least needs an introduction. For this reason we have used it as the standard of comparison for most medium sized birds of the region. Summer travelers in the Sierra Nevada recognize the Western Robin at once as characteristic of the mountains, inhabiting the small meadows which floor the openings in the coniferous forests; people who live in the foothills and valleys of California know the bird as a winter visitor to their orchards, fields, and gardens. Upon the establishment of towns within either its winter or summer range the robin quickly becomes a dooryard bird, regardless of whether the dooryards are those of permanent houses or those of the ephemeral tent cities which, as in Yosemite Valley, grow and vanish with the passage of each summer.

The robin population varies greatly according to place and season. In nesting time the birds are found only in the Transition, Canadian, and Hudsonian zones, in other words, in the boreal parts of the country; and even within this territory their numbers are not uniform, being greatest in the Transition Zone, as exemplified by Yosemite Valley, and smallest about the relatively sparse forests of the Hudsonian Zone, as about Tuolumne Meadows. On the east slope of the Sierras their numbers at best are small.

With the cessation of nesting activities the ties which hold the robins to their summer haunts are broken and the birds begin to range more widely. Food then seems to be the controlling factor in their distribution and continues to be so until they return to their breeding grounds the following spring. An abundance of easily obtained berries may bring about a local concentration of robins in one of the upper zones, and conversely a dearth of forage in the mountains may result in an early departure to the foothills, where adequate forage happens to be obtainable. In 1915 Western Robins were present in the high mountains until late, being seen at Ten Lakes on October 10 and at Aspen Valley on October 15; in Yosemite Valley they were present in numbers up until November 8, when there was a good fall of snow. The next day few robins were to be seen, nor were more than single individuals encountered thereafter, although we remained in the Valley that year until November 22.

Only a few venturesome robins continue in the mountains above the 3000-foot level during the Sierran winter. Two were noted near Clark Bridge in Yosemite Valley on December 10, 1914, and 10 at Gentrys on the Big Oak Flat road on December 30, 1914. On December 28, 1915, about 150 robins were reported at Crane Flat by one of the Park rangers, although no reason was suggested for such a concentration of the birds at that elevation on the date mentioned. In the foothills during the winter months robins are abundant. At Pleasant Valley, 117 were noted in a 3-hour census on December 4, 1915. The return to the higher mountains is accomplished by the birds as early as food conditions permit, irrespective of weather. Only 5 were seen at Pleasant Valley in a 3-1/2-hour census on February 27, 1916; yet the population had not moved much higher into the mountains since none was noted in Yosemite Valley the following day. By the end of April (1916), however, robins had appeared in usual numbers in Yosemite Valley. East of the mountains, the robin population is doubtless altogether absent during the winter months.

Fig. 60. Western Robin in juvenal plumage. Photographed on a porch in Yosemite village, July 31, 1915.

In late spring and throughout the summer the robins go about in pairs when one or the other bird is not in attendance at the nest. After the young are grown, family parties are to be seen for a while. As soon as the young are capable of getting their living independently they gather into flocks. Meanwhile the adults go off by themselves and remain sequestered until completion of their annual molt. Then, in late September, the robins, without regard to sex or age, gather into mixed flocks and, for the most part, spend the winter in such gatherings. These flocks include anywhere from 4 or 6 up to half a hundred individuals. We observed flocks of 10 to 20 in many places in the mountains during September and October, 1915. The flock formation is always loose, and individuals leave and rejoin it at will. For a species like the Western Robin, which subsists largely on crops which fluctuate greatly from year to year as well as from place to place, the flocking habit must be of decided advantage as an aid in locating an adequate supply of food.

The two sexes are very much alike in the robin. Male birds are slightly the larger, their breasts are on the average darker colored, and their bills in summer are nearly clear yellow. Some females are as dark colored on the breast as the lighter males, but their bills are always more or less tinged with dusky. Specimens of robins collected in the late summer show that the plumage of the female is more worn than is that of the male. This may be taken to indicate that to the female falls the greater proportion of the engrossing duties of incubation and caring for the brood. The young, in juvenile plumage, have many rounded black spots which are sharply defined against the whitish or buffy under surface of the body, and the feathers of the back have whitish shaft streaks and black tips. (See fig. 60.) At the post-juvenal molt, in August and early September, the young assume a plumage much like that of their parents; birds of different ages cannot thereafter be distinguished readily in the field. The molt of the adults is not completed until about the first of October. The new feathers of the back have an olive tinge, and those of the lower surface are tipped with white; but these markings are lost by wear as the winter progresses, and give way to the clear slate back and red breast.

The niche occupied by the robin changes with the season. In nesting time the birds live near or upon the ground, save that the males perch high for singing in the morning and evening. They keep to the vicinity of openings in the forest, where there are small trees in which to place their nests and where there is, at the same time, grassland adjacent in which they may forage for worms and insects. The rest of the year they hunt their provender, then largely of a vegetable nature, in trees and bushes, and, for the most part, they fly and perch high above the ground.

The demeanor of a foraging robin depends upon the sort of food the bird is seeking. When hunting insects or worms on the ground, as in a meadow, it will run or hop several paces rapidly and directly, and then stop abruptly ('freeze') in an erect posture and remain very quiet for several seconds before making another advance. Now and then, a robin so engaged will be seen, at the end of an advance, to thrust its bill down into the turf and get something which is swallowed in a demonstrative manner. Presumably hearing as well as sight plays a part in this kind of foraging, and the short periods of quiet and immobility may be for the purpose both of listening and watching for prey which is moving.

The ground foraging habits of the robin are quite distinctive, and, to our way of thinking, effective. After a brief but intent survey of its immediate surroundings, if nothing be discovered, the bird moves speedily on to another location, a few paces distant, and there begins anew its close scrutiny. Only a minimum of time is used in changing position. In this way the Robin covers a large amount of territory rapidly, yet with a high degree of thoroughness. It thus combines the habits of two groups of birds which forage in entirely different ways, those which wait passively in one place and watch for moving prey, and those which hunt actively after food which is stationary. The erect posture assumed by the robin obviously gives the bird a wider field of vision from any one spot, and enables it to see better down into the bases of the grass clumps. The worms and insect larvae which form the bulk of the food obtained in this manner of foraging live, not on the exposed parts of the meadow vegetation, but about the bases of the grass tussocks. The bird probably locates many of these worms by seeing the upper parts of the grass blades move as the worms crawl among or feed upon the roots, just as we sometimes detect the presence of a pocket-gopher by seeing a plant shake violently when the animal is gnawing at the root. The periods of quiet between the changes of position by the robin probably subserve another function, namely, that of permitting the worms to become active again after their initial alarm. Any person who has dug angleworms for fishing will recall how sensitive the worms are to ground vibrations, even of a very slight nature, and how the worms will withdraw into their burrows and remain there until the disturbance has ceased. It may well be that these quiet poses by the robin give the worms time for reassurance, time to become active again, and thereby to betray their locations to the foraging bird.

The robin never digs with its bill as does a thrasher, nor does it scratch out food with its claws as does a fox sparrow. Structurally it is not adapted for either of these methods of foraging, for it is a 'soft-billed' bird, the sign of an eater of insects, worms, and berries.

In winter, when seeking chiefly vegetable food, the behavior of the robins is quite different. Then, caution as regards noise or movement seems to be almost entirely lacking, and the birds jump and flutter about actively, meanwhile uttering many short notes. They seem excitable at this season, at least when busily foraging, and are often ill content to stay long in one place. But when gorged with food they are likely to remain quietly perched in some leafless tree until the process of digestion has so far advanced that they can begin feeding again. In this latter respect their behavior recalls that of waxwings.

The song of the Western Robin is a conspicuous feature in the daily chorus of mountain bird voices. It is usually the first real song of the morning. Even before the coming of the faintest streaks of dawn the robins have begun their caroling, and in places where they are at all numerous, as in the Yosemite Valley, the forest and the granite cañon walls resound with their voices. For song perches, they seek the tips of exposed branches such as are reached by the first direct rays of the morning sun. The song consists of a long series of full rounded reverberant notes, grouped into bars with definite rests between. The notes are pretty much all on the same key, yet there is a distinct and alternate rising and falling of inflection. The songs of the Western Robin and Black-headed Grosbeak are sometimes confounded, but that of the latter bird is more varied, is given in quicker time, and it contains many little trills or shrill warbles not to be heard at all in the robin's song. To our ears the song of the robin does not compare in quality with that of many other birds of the mountains, as, for example, that of the Sierra Hermit Thrush and the Townsend Solitaire. After a time the robin's song becomes actually wearisome because of its monotony.

As the heat of the day increases, the robins become less voluble and take to foraging in the meadows, or resting silently on the lower branches of the trees. With the approach of early evening they become tuneful again. But as dusk comes on, the full songs are less frequently heard, and these are much interspersed with the loud unmusical cries and 'squeals.' At late dusk, when the birds are arranging and rearranging themselves for the night on their favorite perches high in the tall trees, they accompany the many short flights and changes of position with a multitude of the short calls. Sometimes these evening exercises of the robin become accentuated to an extreme degree. A bird will dash about wildly, resting on one perch for an instant, to sing a few bars of song, then darting to some other tree, and singing again, or else uttering a series of the loud cries. In early summer, robins in the Yosemite Valley have been heard singing as late in the evening as eight o'clock, long after the dusk of twilight had filled all but the most open portions of the Valley floor.

With the passage of the nesting season the full song is less often heard; our latest record of a song given fully is for July 3 (1915) at El Portal. Thereafter there are only a few occasional snatches of the song, as well as the usual shorter calls. During the period of molt the birds are practically quiet. As they gather in flocks for the winter their voices are heard again, but not in regular song. Their vocal disturbances while feeding and when going to roost of evenings become louder and louder so that in places where there is a large number of robins their calls rise into a veritable babel of voices. Not until February or March are the real songs again given with full strength.

The call notes of the Western Robin, as already intimated, are various. An attempt at expressing some of them in syllables, such as might be uttered by the human voice, is as follows: tuk, tuk; tche'-ah or wi'eh (a sort of squeal); wee', kuk-kuk-kuk.

Robins nest abundantly in the Yosemite region and their activities while engaged in the construction of their nests and the rearing of their broods are open to easy observation. Nest construction in the Transition Zone as exemplified by Yosemite Valley was in progress on April 30, 1916; and in mid-May, 1919, nests with eggs were fairly common. A nest with 4 fresh eggs, in which the parent was sitting, was seen at Hazel Green on May 14, 1919, and on the same day other birds were seen carrying building materials. On May 25, 1919, a nest with young was seen in Yosemite Valley. At the McCarthy ranch, 3 miles east of Coulterville spotted-breasted young, out of the nest, were seen on June 4, 1915. Nesting continues well into summer, for on June 14, 1915, in Yosemite Valley, a female robin was seen gathering nest material. A parent bird was observed feeding young in the nest in Yosemite Valley on July 15, 1915. This last date is the latest for nesting known to us at the time of writing, although it seems likely that still later instances of young in the nest are to be found. In any event, visitors to the Yosemite Valley are likely to see robins engaged in one phase or another of the nesting program from the first of May until toward the end of July, a range in nesting time probably not exceeded by that of any other bird in the Valley. Higher in the mountains the season is somewhat later. Adults were seen carrying food at Tuolumne Meadows on July 7, 1915, but no young were noted out of the nest at that station by the date mentioned. East of the mountains, at the Farrington ranch, near Williams Butte, on April 29, 1916, a robin was seen brooding on a nest; on May 9 another bird was found, near Walker Lake, on a nest containing 3 eggs; and adults were carrying food to young at Mono Lake Post Office on June 30, 1916.

The nest of the Western Robin is a stoutly constructed affair, composed of grasses and weed stems, pine needles, or similar material, and well plastered with mud. (See pl. 55a). The site chosen for the nest varies with circumstances, as does the height at which it is placed above the ground. Probably a majority of the nests are placed in small trees at the edges of clearings; but there are many exceptions. We have noted nests in good-sized sugar, yellow, and lodgepole pines, in firs, black oaks, willows, and cottonwoods, and one was seen on a shelf in a farm shed. The height of nests above the ground ranges from 4 to 75 feet in observed instances, although a majority are probably at a height of less than 12 feet. A nest in a young coniferous tree is usually placed near the top, against the trunk, and supported by one or more small horizontal branches. A nest in a black oak or a willow, especially if the tree be a large one, is apt to be located in a slanting or upright crotch; in the biggest pines, a large outswaying branch is a favorite site. Several were noted amid unusual surroundings. In Yosemite Valley in 1919 there was a nest in a remarkably exposed situation in a willow which grew at the side of the main traveled road between the village and Camp Curry, where the road borders directly on the Merced River. Many people, both walking and in automobiles, passed the spot daily, but the parent bird stayed persistently on the nest. In June, 1920, a robin was sitting in her nest on a beam just above the office entrance at Camp Curry. Many hundreds of persons passed daily just beneath her. In a willow tree beside the river above Stoneman Bridge another robin had built her nest early in May, 1919. With the rise of the water at flood time the tree was entirely surrounded by the swirling current 3 or more feet deep; but undaunted, the parent stayed at her post, incubating her eggs.

A typical nest measures outside about 4 inches in height by 6 or 7 inches in maximum breadth. The cavity is about 3-1/2 inches across by 2-1/2 in depth. In some, the mud used is located only in the basal portion; in others there is a smooth rim of mud at the top. The outside height of a nest depends somewhat on its location. Those nests saddled on large horizontal branches are least in volume.

The method of construction and the industry of the robin in carrying on the work of nest building may well be shown by direct quotation from one of our field notebooks.

Yosemite Valley, April 30, 1916. Found a robin engaged in building a nest 12 feet above the ground on a 3-inch horizontal branch of a big (4-foot) yellow pine. Very exposed situation, without any sheltering foliage. I watched the bird for over half an hour. Its schedule was as follows:

8:7:25 A.M. Flew to mud at small drainage ditch about 150 yards away.

8:7:50. Returned with small ball of mud in bill; placed this in bottom of nest, then got in latter (which was deep enough to shelter bird from chin to base of tail), threw its breast forward, tilted up its tail, held its wings well up (but not extended) on back, and 'tamped' mud into place by forcing breast against wall of nest; after several thrusts in one direction the bird rotated itself slightly and tamped again. This was kept up until more than one complete revolution had been made. This rounds the nest, and forces the mud into the interstices so that it holds together the grasses, string, etc., which form basis of nest. Mud was noted on breast feathers of bird when it emerged.

8:13:25. Bird left nest and went toward Yosemite Creek, a different direction from where other mud was obtained.

8:15:55. Returned with stringy mud; tamped.

8:17:50. Left nest and went to first source of mud.

8:19:00. Returned with moderate sized ball; tamped; lit on nest edge and not on usual twig.

8:21:00. Off to Yosemite Creek.

8:23:45. Returned with mud evidently containing leaves; tamped.

8:26:10. Off to Yosemite Creek again.

8:30:05. Returned with mass of stringy mud; tamped.

8:35:45. Off to Yosemite Creek again.

Several trips were made before I began timing the bird. Often, as it was tamping it would catch a free end of grass at the nest edge and tuck it down in. The tamping and circling serves to make the nest strong, regular, and smooth, so that it can shelter the eggs and young securely. The mud is very wet when gathered, as I found by visiting the place where the first lot was obtained. The bird always came directly to the nest, even when, as it approached, I was on the ground and in plain sight between it and the nest.

This particular robin, as we see, was bringing a fresh lot of material every five to ten minutes, and during the period when it was under observation it worked without a rest. After the nest is completed there is usually an interval of a few days before egg laying commences. This affords time for the mud to dry thoroughly.

The eggs of the robin are of a uniform deep blue color, with a slight greenish tinge, but without spots of any sort. The shells have a dull surface appearance which is characteristic of the eggs of this species. Four eggs are commonly to be found in the nest of the robin; yet we did not see more than 3 young robins in any one brood, within the nest, or out with the parent birds. Whether any one pair of robins in the central Sierra Nevada rears more than a single brood in a season is not known to us.

Not until all the eggs in a set are laid does the work of incubation begin; thenceforth it is carried on without cessation. Often the sitting bird can be approached very closely before it will leave the nest. The cup-like shape of the nest is such that the bird can sink its whole body down into the cavity, until only its head and tail project at steep angles above the rim. Once one of our party came upon a robin as the bird sat on its nest in the top of a small fir tree. The bird seemed startled by the observer's sudden appearance and left the nest immediately, flying to another tree fifty feet away where it began to squall loudly, making such a noise that it attracted to the spot a Sierra Red-breasted Sapsucker and a Mariposa Fox Sparrow.

Ranger Forest Townsley has told us that in Yosemite Valley he has seen one member of a pair of Robins (the male?) feed the other (the female?) while the latter sat upon the eggs. It is our impression that most of the robins which we saw abroad during the middle of the day in the early part of the nesting season possessed richly colored breasts and clear yellow bills, and hence were probably males. This fact would tend to substantiate Mr. Townsley's observation.

The general nature of the robin's food has been alluded to in several of the preceding paragraphs. Further remarks are in order. In the nesting season the birds feed largely on worms and insects, but in other parts of the year their subsistence is gained mainly from berry-producing trees and shrubs. At Walker Lake, in mid-September, 1915, robins were feeding on berries of the red elder, and at Glen Aulin, later the same month, in company with Townsend Solitaires, the robins were eating the berries of the western juniper. In Yosemite Valley in early November, 1915, they were taking chokecherries and coffee berries, while at Gentrys on December 30, 1914, the few robins seen were eating the dry sticky-coated berries of the manzanita (Arctostaphylos mariposa). Robins are quick to take advantage of easily obtained food of a sort to their liking. Many persons who sojourn in the Yosemite region during the summer months find the robins ready visitors to their "bird feeding tables." The picture of a spotted-breasted young shown herewith (fig. 60) was obtained at one of these feeding places on a porch in the Yosemite village.

The robin's adaptability in the matter of food, and also its instinctive haste to cleanse its nest of any débris, were both illustrated by an incident which transpired on June 20, 1915, at Chinquapin. A robin was seen to fly away from its nest nearby carrying in its bill something which looked like a mouse dangling by the tail. The bird happened to drop the object within the camp precincts and it proved to be a juvenile robin (with feathers still in the sheaths). The old robin had obtained a large piece of liver from a pile of discarded mammal bodies and had carried this material to the youngster as food. When the young bird had swallowed as much of the liver as it could hold, a portion still protruding from its mouth. The parent, in haste to clean the nest, had picked up the free end of the piece of liver, not appreciating the fact that the youngster had swallowed the other end, and had carried both the liver and the young robin out of the nest.

Mr. Donald D. McLean has recorded (1919, p. 160) the finding of remains of six Western Robins in the stomach of one female California Wildcat killed by him March 10, 1919, near Coulterville. At Chinquapin on May 20, 1919, a robin was seen flying at a Sierra Chickaree, snapping its beak loudly, until it forced the squirrel to descend the tree. The evidence is only circumstantial, but might indicate that the squirrel had invaded the robin's nesting precincts. Much further and careful observation must be made before the enemies of the robin are well known.

Toward the latter part of June, 1920, in Yosemite Valley, at least four young robins were picked up in which the plumage was oil-soaked, evidently as a result of the birds having bathed in pools of water upon which oil had been sprayed to kill mosquito larvae. One of these birds was nearly dead; the others were obviously not in normal condition. Here, then, is another way in which man's activities interfere with the course of events in nature.

Partial albinism is not an uncommon phenomenon in the Western Robin. Two instances came to our attention in the Yosemite region, in both of which the birds in question had some white feathers on the head. Complete albinos are much rarer, as are melanos (abnormally dark colored individuals). In a bird of the size and habits of the robin, abnormalities in coloration are much more likely to be observed and commented upon than are similar occurrences among the smaller and more retiring species. In any event, albinism is merely the outward physical manifestation of some defect, local or general, in the tissues or body processes of the animal in which it occurs, and does not warrant the attention which has been directed to the subject by some scientific as well as many lay students.