Part 40

There can be no doubt, however, that young males breed in this immature plumage, for Price (1895) secured a pair that were feeding a brood of young, and the "male was not in fully adult plumage and was very similar in coloration to the female." Swarth (1904) writes: "The male bird breeds in the immature plumage, for on June 21, 1902, I assisted O. W. Howard in securing a nest, containing four eggs, the parents of which were indistinguishable in color and markings. * * * I was surprised at the large proportion of birds in this immature plumage that were seen. At a very liberal estimate I should say that the males in adult plumage comprised barely a third of the birds seen in the spring."

Adults have a complete postnuptial molt, mainly in July; all June birds that I have seen are in worn plumage, and August and September birds are in new, fresh feathers. The fall plumage of the male is similar to that of the spring male, but the colors of the head, neck, and chest are duller, more clay color, the back is more olive and the sides are browner. In the female at this season the crown is tipped with grayish and the throat and breast with buffy, while the sides are browner than in the spring; the white tips of the greater wing coverts are tinged with yellowish. The nuptial plumage is acquired mainly, if not entirely, by wear, the edgings wearing away and the colors becoming brighter.

Food.--Nothing definite seems to have been recorded on the food of the olive warbler, but its habit of creeping over the branches and twigs of the pines, much after the manner of the pine warbler, would seem to indicate that it was foraging for the many small insects that infest these trees. It is evidently one of the protectors of the pine forests. Brewster (1882b) says: "In their actions these Warblers reminded Mr. Stephens of Dendroeca occidentalis. They spent much of their time at the extremities of the pine branches where they searched among the bunches of needles for insects, with which their stomachs were usually well filled. Occasionally one was seen to pursue a falling insect to the ground, where it would alight for a moment before returning to the tree above."

Behavior.--One of the members of Henshaw's (1875) party brought in a specimen of this warbler, on September 20, "which he stated he had shot from among a flock of Audubon's Warblers and Snowbirds, which he had started from the ground while walking the pine woods. With the rest, it had apparently been feeding upon the ground, and had flown up to a low branch of a pine, where it sat and began to give forth a very beautiful song, which he described as consisting of detached, melodious, whistling notes."

W. E. D. Scott (1885), writing of his field work in the Santa Catalina Mountains in late November, says:

Associated with flocks of the Mexican Bluebird (Sialia, mexicana), which was, by the way, the only kind of Bluebird observed, was always to be found one and sometimes two representatives of the Olive Warbler (Peucedramus olivaceus). The Bluebirds were generally feeding on some insects in the tall pines, in flocks of from six to ten individuals. The Olive Warblers were on the best of terms with their blue friends, and as the Bluebirds were shy and restless they made it difficult to obtain or observe very closely their smaller allies. I did not in these pine woods see the two species apart, and became at length so well aware of the intimacy that existed between them, that I would fire at any small bird passing high overhead in company with Bluebirds. They were chance shots, certainly, but the only two small birds obtained flying in this way with the Bluebirds were Olive Warblers. * * * Generally they preferred the largest branches of the pines when they alighted, though I took one not more than three feet from the ground in a small bush. Their movements while feeding or searching for food are very deliberate, though I noticed now and again certain motions when at the extremity of a bough that reminded me of a Kinglet or a Titmouse.

Swarth (1940) says: "Though frequenting the tree tops to a great extent, they seem singularly tame and unsuspicious, and several times I have had one feeding in some of the lower branches, within arm's reach of me, without its showing the least sign of fear."

Voice.--The olive warbler has a rather loud, attractive, and distinctive note, but few observers have referred to it as a song. The "beautiful song" mentioned above consisted of "detached, melodious, whistling notes."

One of its whistling notes sounds very much like the peto note of the tufted titmouse and might easily deceive the listener. Scott (1885) observed that these warblers "had a call-note so like that of their associates [the bluebirds] as to be almost identical. It seemed to me only a clearer whistle of more silvery tone." Price (1895) saw a male alight on a twig near his mate, during nest-building, uttering "a liquid quirt, quirt, quirt, in a descending scale." Mr. Henshaw (1875) heard "a few strange Vireo-like notes coming" from an olive warbler. A bird that Dr. W. P. Taylor (MS.) watched in apparent courtship gave "a whistled call with descending inflection."

Field marks.--In general appearance and behavior the olive warbler suggests the pine warbler, especially as it creeps over the pines. The orange-brown head, neck, and breast of the adult male, with the conspicuous black band through the eye, is distinctive; these colors are much paler and more yellowish in the female, and the band through the eye is grayish. Both adults have two white wing bars, a white area at the base of the primaries and much white in the tail, the white areas being more restricted in the female. Young birds are much like the female (see descriptions of plumages).

Winter.--The olive warbler, as a species, is probably permanently resident throughout most of its Mexican and Central American range. But the northern olive warbler is evidently partially migratory, though some individuals, perhaps many, remain in Arizona during part, or all, of the winter. All of the 15 specimens taken by Stephens for William Brewster (1882b) were collected in March, probably too early to be migrants, and he says that Stephens had previously taken one in February 1880, evidently a wintering bird. Mr. Swarth (1904) writes: "I have not found this species very abundant in the Huachucas at any time, but it is probably resident to some extent, for I secured an adult male on February 21 when the snow was deep on the ground. During March I saw several more, all adult males and single birds, usually with a troop of Pygmy Nuthatches; but it was not until the first of April, when the other warblers were arriving, that they became at all abundant." Scott (1885) found them on the Catalinas under winter conditions, with snow on the ground, and says: "I think there can be little if any doubt that they are residents all the year." And Dr. W. P. Taylor (MS.) took one in the Santa Ritas on February 4, 1923. Just how far south go the birds that migrate away from Arizona does not seem to be known, but apparently they have not been detected beyond Chihuahua and Tamaulipas. Perhaps they do not migrate at all.

DISTRIBUTION

Range.--Southwestern United States to northern Nicaragua.

Breeding range.--The northern olive warbler breeds =north= to central Arizona (Baker's Butte and White Mountains) and central western New Mexico (Reserve). =East= to western New Mexico (Reserve and McKnight's Canyon); Chihuahua (Colonia García); southeastern Coahuila (Diamante Pass); and southwestern Tamaulipas (Miquihuana). =South= to southwestern Tamaulipas (Miquihuana) and southern Durango (Durango). =West= to Durango (Durango); Sonora (Sierra Saguaribo); and southeastern and central Arizona (Huachuca Mountains, Santa Catalina Mountains, and Baker's Butte).

Other races occur in southern Mexico and Central America.

Winter range.--The northern olive warbler is probably migratory to some extent, individuals withdrawing to the southern part of the range, but it is found in winter occasionally or in small numbers as far north as southern Arizona.

Egg dates.--Arizona: 14 records, May 23 to July 1; 7 records, June 2 to 18, indicating the height of the season.

DENDROICA PETECHIA AESTIVA (Gmelin)

EASTERN YELLOW WARBLER

PLATES 24, 25

HABITS

The familiar yellow warbler, also commonly called the summer yellow bird or wild canary, is the best known and the most widely known of all of our wood warblers. It is one of the few birds that almost everybody knows by one of the above names. It is universally beloved as it comes to us in the flush of budding spring, gleaming in the shrubbery, like a rich yellow flame among the freshly opening leaves, or bringing to the apple orchards a flash of brilliant sunshine to mingle with the fragrant blossoms. As Dr. Chapman (1907) says: "In his plumes dwells the gold of the sun, in his voice its brightness and good cheer. We have not to seek him in the depths of the forest, the haunt of nearly all his congeners, he comes to us and makes his home near ours."

The yellow warbler, as a species, is also the most widely distributed member of its family. Its breeding range extends from the Atlantic to the Pacific in both Canada and the United States (110 degrees of longitude), and from the Barren Grounds in northern Canada to Mexico and the Gulf States (40 degrees of latitude). Its winter range covers 54 degrees of longitude and 31 degrees of latitude in Central and South America. Professor Cooke (1904) says: "The extreme points of the yellow warbler's range--northern Alaska and western Perú--are farther separated than the extremes of the range of the black-polled warbler, which is considered the greatest migrant of the family." But it must be remembered that the yellow warbler breeds much farther south than the black-poll.

Spring.--The spring migration of the yellow warbler is long and partially circuitous; eastern yellow warblers that winter as far east as British Guiana probably make a roundabout flight to Central America, as there seem to be no springtime records for this bird in the West Indies and few for it in Florida. These birds may fly across the Gulf from Yucatán to Cuba and Florida, but the main flight is probably directly north from Yucatán to Louisiana and other points on the Gulf coast; they have been repeatedly seen flying northward in the middle of the Gulf. There is also a considerable migration along the coast of Texas, which I have personally observed.

The migration is also prolonged or very irregular, for according to the dates of departure given to me by Alexander F. Skutch (see under Winter), the last of these warblers do not leave Central America until the very last of April, or the first of May, after the first arrivals have reached New England; some of these records, however, may apply to one of the western races. After the birds reach the United States, the migration fans out northward and northeastward and seems to be more rapid. Of this Frederick C. Lincoln (1939) says: "Coming north from the Tropics these birds reach New Orleans about April 5, when the average temperature is 65° F. Travelling on northward much faster than does the season, they reach their breeding grounds in Manitoba the latter part of May, when the average temperature is only 47°. Encountering progressively colder weather over their entire route, they cross a strip of country in the 15 days from May 11 to 25 that spring takes 35 days to cross. This 'catching up' with spring is characteristic of species that winter south of the United States and of most of the northern species that winter in the Gulf States."

Territory.--Soon after their arrival on their breeding grounds the males begin to select their territories and then to defend them. Dr. S. Charles Kendeigh (1941) made a study of the territories of birds in a prairie community in northwestern Iowa, and writes:

A special study of the Yellow Warbler indicated that territorial requirements included suitable nest-sites, concealing cover, tall singing posts, feeding areas in trees, and space, and that when certain of these factors were lacking, territorial relations became confused and the behavior of the birds was modified. * * * These warblers possessed territories that averaged about 150 feet in diameter, or approximately two-fifths of an acre. Even in locations where trees were included, the territories appeared to be of about the same size. The limits of the territory often did not coincide with the boundaries of the thicket in which the nest was located but extended over the neighboring grassland and often included parts of neighboring thickets. These territories were defended by the males partly by singing, although in shrubby areas lacking trees they were handicapped by lack of singing posts from which to proclaim their ownership and to advertise themselves. A few made use of fences from which to sing and also of tall posts and wire from an abandoned electric line that extended through the area. The rôle of the female in defense of territory was not determined.

Probably due to this lack of singing posts and to the unusual abundance of birds, chasing was also extensively used as a defense measure, and during the height of the nesting season squabbling birds were a common sight all over the area. * * * Neighboring males seemed to lack any conception of the limits of each other's territories and moved about indiscriminately until chased out. No actual fighting was observed. * * * In other parts of the area where trees were available, the males commonly sang at a height of 18 feet, often up to a height of 45 feet, and chasing was not often observed.