Notes on the Food Habits and Food Defense of the Acorn Woodpecker

Abstract

The Acorn Woodpecker (Melanerpes formicivorus), the most social of North American woodpeckers, is a common resident of mixed oak woodlands from Oregon south through California, east through Arizona, New Mexico and Texas, and south to Panamai. These woodpeckers live in year-round groups. Each group consists of 2-10 birds of both sexes and apparently all ages (Ritter 1938). In most groups males are reported to outnumber females, but this apparent discrepancy in sex ratio may be explained by the fact that juveniles possess the adult male plumage during at least part of their first year (Ritter 1938). Territory and food defense, nest hole construction, and the care and feeding of nestlings appear to be accomplished jointly by all members of the group. Aside from these rather sketchy points, little else is known about the social organization of these woodpeckers. In its food habits, the Acorn Woodpecker is one of the most atypical of all woodpeckers. During the fall and winter the birds feed extensively on acorns and other mast which they store in prepared holes in the surfaces of oaks and pines. This aspect of their ecology has been repeatedly described (see literature cited in Ritter 1938 and in Bent 1939), but because of a predominance of interest in this unusual habit, other aspects of the woodpeckers' food habits have been largely neglected by most naturalists. This is unfortunate since it has led to the assumption that the food habits of these birds are far less diversified than is actually the case. In addition to storing and consuming dried acorns, the woodpeckers feed extensively on mature and immature green acorns before storage begins during the fall, and are proficient flycatchers and sapsuckers. The purpose of this paper is threefold: 1) it describes some previously unreported or incompletely described aspects of the food habits of the Acorn Woodpecker; 2) it describes the defense of these foods from conspecifics and heterospecifics; and 3) it compares some aspects of the food habits of the Lewis' (Asyndesmus lewis), Acorn, and Redheaded (Melanerpes erythrocephalus) Woodpeckers. Since the food habits of the Acorn Woodpecker have been the subject of several previous papers (see literature cited by Beal 1911, Ritter 1938, and Bent 1939), a repetition of these earlier works is avoided.