VERMIVORA CRISSALIS (Salvin and Godman)
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.