Natural History, Variation, and Distribution of the Strickland's Woodpecker

Abstract

Strickland''s woodpecker (Dendrocopos stricklandi) was studied in Mexico from Jan. through May, 1961, and in southeastern Arizona in June and July, 1961. The sp. includes 2 groups. The arizonae group includes a series of populations characterized by dark brown pileum and nape, medium brown dorsum and rump, upper parts immaculate or nearly so, and underparts spotted and barred. This group ranges from southeastern Arizona and southwestern New Mexico south to the east-central part of the Mexican state of Michoacan, and it occurs between about 4,000 and 8,000 feet, occasionally higher. The stricklandi group is characterized by dark, sooty brown coloration, heavily white-barred dorsum and rump, and streaked and barred underparts. It occupies high elevations, between 8,500 and 13,500 feet, in the Mexican states of Mexico, Morelos, Puebla, and Veracruz, and in the Distrito Federal. In the northwestern part of its range the arizonae group forages mainly in oaks. In the southeastern part of its range, populations of the arizonae group occur almost entirely in pine woodland. The stricklandi group occurs in woodlands and forests which are dominated by conifers, especially by pines, with oaks and alders interspersed as less prominent elements. In dimensions, there are 4 generally concordant northwest-southeast clines of decreasing size of bill, wing, tail, and tarsus in the arizonae group. Bill size continues to decrease sharply in the stricklandi group, but wing and tail lengths increase markedly, with abrupt reversal of the clines in those dimensions. Tarsal length shows less clinal variation than the other dimensions. The relatively long wing and tail of stricklandi may reflect adaptation to flight in the less dense atmosphere of high altitudes. The very small bill of the stricklandi group may reflect dependence on conifers as primary foraging sites, reinforced by selection pressures exerted by climate in accordance with Allen''s Rule. There is a further possibility that the very small bill of the stricklandi group may reflect a foraging method different from that used by arizonae. The arizonae and stricklandi groups are similar in coloration of the pileum and nape. They differ strongly and consistently in depth of color of the dorsum and rump and in ventral pattern. They differ less consistently, but to a considerable degree, in extent of the red on the head in adult males. Without the test of sympatry, the two groups are here regarded as conspecific, thus emphasizing allopatric distribution, similarities in dorsal pattern, in pileum and nape color, in vocalizations, and in ecology of the two groups where they approach geographically. The recently named race websteri Phillips, originally described from Nayarit and western Jalisco, is recognized on the basis of size differences but is here given a more extensive range.