Part 33

COLIMA WARBLER

CONTRIBUTED BY JOSSELYN VAN TYNE

HABITS

Described in 1889 from a single specimen collected by W. B. Richardson in the Sierra Nevada de Colima, Mexico, this handsome warbler was, in 1932, still known from only a dozen museum specimens, and not a word had been recorded on its habits. In that year a University of Michigan expedition found the Colima warbler to be common in the higher forests of the Chisos Mountains of southwestern Texas and made the first discovery of its nest and eggs. The basis for the inclusion of this warbler in the A. O. U. Check-List had been a single specimen collected by Frederick M. Gaige in the Chisos in 1928 (Van Tyne, 1929).

The range of the Colima warbler has been recorded only very sketchily, but Bangs (1925) was probably correct in surmising that the specimens from southern Mexico (Colima and Michoacán) were migrant birds. The closely related Virginia's warbler, which nests in the Rocky Mountain States, winters mainly in Michoacán, Guerrero, and Jalisco. Recently R. T. Moore (1942) added a second, more southerly, locality in Michoacán and one in eastern Sinaloa to the known southern range of the Colima warbler. The breeding range is apparently restricted to the highlands of northeastern Mexico and the Chisos Mountains of southwestern Texas. In Texas the Colima warbler occurs at altitudes between 6,000 and 7,500 feet (Van Tyne, 1936); in Coahuila, apparently, only above altitudes of approximately 7,500 feet (Burleigh and Lowery, 1942). Records from the southern part of its range, however, show a greater altitudinal spread. The type specimen was taken in Colima at about 8,000 feet, and R. T. Moore (1942) reports two November specimens, one taken at 9,500 feet in northeastern Michoacán, the other at 5,200 feet in Sinaloa. These represent the extremes of the known altitudinal range.

Courtship.--Mating behavior has been observed during the first few days of May and sets of eggs noted May 15 (just completed) and May 20 (highly incubated). The only recorded specimen in juvenal plumage was collected July 20. Peet observed pursuit behavior in the Chisos Mountains on May 4 (within a few days of nest building), which may have had some courtship significance, but nothing definite is known of the courtship habits. Sutton noted copulation twice on May 1 in the Chisos, and the gonads of specimens collected that day were much enlarged; there was no indication that the females had begun incubating.

Nesting.--Two nests, both in the Chisos Mountains, have been described. The first (discovered in 1932) was lodged between small rocks and deeply imbedded in dead oak leaves on the sloping bank of a dry stream bed. A dense ground cover of vines and other herbaceous plants arched completely over it, leaving an entrance only on the northwest side, toward the stream. The nest had a basic structure of loosely woven fine grasses, the outside reinforced with pieces of green moss and the rim with strips of cedar bark; the cavity (5 centimeters across the rim and 4 centimeters deep) was lined with fine grass, a little fur, and a few hairs (Van Tyne, 1936). The other nest, which was "on the ground, under a little bunch of oak leaves, at the edge of a talus slope, almost at the very base of the cliffs" (Sutton, 1935), was similar, but its basic structure included dry leaves, and the site was concealed by only a partial canopy of leaves (Van Tyne and Sutton, 1937).

Nest building was observed in the Chisos Mountains on May 7, 1932 (Van Tyne, 1936):

As I was crossing the dry stream bed about a hundred yards below Boot Spring, I suddenly saw within twenty-five feet of me a female warbler with nest material in her bill. I stopped instantly and, remaining motionless, was greatly relieved to see the warbler continue undisturbed by my presence. In a moment she dropped to the ground and entered the nest, which was on the sloping right bank of the stream about six feet back from the margin of the rocky stream bed. After working for about twenty seconds the warbler left the nest and flew down the stream bed a hundred and fifty feet. In twelve minutes she was back with more nest material to repeat the performance. Subsequent excursions for building material during the ensuing hour were of three, twelve, six, and twenty-two minutes' duration. Each time she worked at the nest only fifteen to twenty seconds, until the last trip (at 11:43 A. M.) when she worked about two minutes and then departed, probably to feed, for she did not return again while I watched. Each trip to the nest had been made undeviatingly, without any hesitation, from the stream bed or from the forest to the west. Alighting almost directly above the nest, without a pause she dropped through the branches by three or four stages and promptly entered the nest, placed the material, and snuggled down working it into place. After a few moments she seemed to have completed this to her satisfaction, and, leaving the nest, she flew up to the branches ten or twelve feet above, fed for a few moments on the insects among the fresh green leaves of the little oaks and maples, and went away for more material.

When it was evident that the nest building was over for the time I went over to the nest and, examining it more closely, found that it was nearly built. The following day, May 8, it seemed to be finished.

Eggs.--Two complete clutches have been found, each containing four eggs. Four eggs collected and measured were 18 by 13.3, 18 by 13.5, 18 by 13.5, and 18.5 by 14 millimeters. They were creamy white, speckled, and blotched in a wreath at the larger end with "vinaceous fawn," "light brownish drab," and "cinnamon drab."

Egg laying, in the one instance observed, was at daily intervals (May 12-15); the first egg was laid four days after completion of the nest. Incubation had begun May 16, the day after the last egg was laid. The length of the incubation period is not known. Females collected on May 12 (Peet), May 17 (Van Tyne), and May 20 (Sutton) had well-marked incubation patches; males collected at the same time had no patch.

Plumages.--The Colima warbler differs from its nearest relative, the Virginia's warbler, in being larger; darker, less gray, above; crown paler; rump and upper tail coverts darker and richer in color; yellow of throat and breast absent or, if present, more green and more diffuse; sides and flanks more brownish; crissum darker, more aniline yellow; sexes much more nearly alike. The adult female Colima warbler is slightly darker than the male and is more brown below. It is apparently never yellow on the breast.

The juvenal plumage (known from only one specimen) differs from the adult plumage in lacking the crown spot and in having two buffy wing bars. The rump is also much more yellow (less green) and the crissum is more yellow (less orange). The young Colima warbler differs from the young Virginia's warbler in having a larger bill, darker plumage, and a less ochraceous rump.

The fall plumage differs from that of the spring in being "darker and browner throughout, the gray of head a good deal obscured by deep olive or light brownish olive; crown patch orange rufous; under parts darker with whitish area in middle of belly more distinct and under tail-coverts duller, more nearly aniline yellow" (Bangs, 1925).

George Miksch Sutton's fine color plate (Van Tyne, 1936, frontispiece) of the Colima warbler is apparently the only published figure of the species.

Behavior.--In Texas, the Colima warbler was observed feeding on insects (which were not identified), but nothing further has been recorded about its food. All observers seem to agree that it is not a shy bird, although in its preferred cover, the female seems elusive and nests are difficult to find. Sutton has remarked that they are "rather deliberate, even vireo-like in their movements" (Van Tyne and Sutton, 1937). In the Chisos Mountains, they frequented especially the young maples and deciduous oaks along the banks of the dry, boulder-strewn stream bed, and elsewhere on the steep mountain slopes their preference for clumps of small oaks was noted.

Voice.--The call note of the Colima warbler is a very sharp, almost explosive psit. Its common song is a continuous trill, like that of the chipping sparrow, but shorter (lasting 3 to 4 seconds), more musical, and ending with two separate notes slightly lower in scale. A second, rarer, and more varied song is so clear that it can be heard for three or four hundred feet through the woods although it does not seem loud when heard from nearby. It is perhaps this song that Brandt (1940) describes as resembling the song of the eastern redstart. E. C. Jacot (MS.) reports that the males usually start singing when "a person approaches the territory of a pair, and continues to sing until the intruder has passed." In the Chisos Mountains, Tex., the males were persistent singers. Once several sang even after a dense fog had silenced most other species. They sang usually from bushes and small trees between periods of feeding and moving about but sometimes remained for a while on a higher perch (up to 20 feet), singing at frequent intervals.

DISTRIBUTION

Range.--Chisos Mountains, Tex., and mountains of northeastern Mexico; probably winters in Colima, Michoacán, and Sinaloa.

The Colima warbler has been recorded from: Texas (Chisos Mountains); Coahuila (Sierra Guadalupe and Diamante Pass); Tamaulipas (Miquihuana); Michoacán (Patamba and Sierra Ozumatlan); Sinaloa (5 miles north of Santa Lucia); Colima (Sierra Nevada).

Egg dates.--Texas: 2 records, May 15 and 20.

VERMIVORA LUCIAE (Cooper)

LUCY'S WARBLER

PLATES 18, 19

HABITS

Dr. J. G. Cooper discovered this tiny and inconspicuous warbler at Fort Mojave, on the Arizona side of the Colorado River, in the spring of 1861, and named it in honor of Miss Lucy Baird, daughter of Prof. Spencer F. Baird. It might well have been named the mesquite warbler, as its distribution coincides very closely with that of this tree, which seems to furnish its favorite home, most of its nesting sites, and much of its foraging area.

Harry S. Swarth (1905) wrote of conditions then existing: