Acorn Woodpecker Breeding Strategy as Affected by Starling Nest-Hole Competition

The aggressive, skillful tactics used by the introduced Starling (Sturnus vulgaris) in acquiring nest-holes have been extensively documented by Kalmbach and Gabrielson (1921), Howell (1943), Bent (1950), and others (see below and Troetschler 1970), but it is not known whether the Starling is detrimental to the breeding success of any native North American bird. The present study was designed to determine if competition with Starlings for tree holes is changing the breeding strategy and/or lowering the fecundity of the Acorn Woodpecker (Melanerpes formicivorus) in California. The Acorn Woodpecker is a unique, social species resident in the oak belt of western North, Central and South America. Individuals live and breed cooperatively, defend stores of acorns (each acorn tightly fitted into a woodpecker-made socket) and collectively defend a year-round territory which includes the nest tree(s), storage tree(s), and oaks which supply the mast (Myers 1923, Leach 1925, Ritter 1938, Skutch 1943, 1961, 1969, MacRoberts 1970, MacRoberts and MacRoberts 1972). It seems possible that this species has an advantage over other competitors for Starling holes such as bluebirds, flycatchers or other woodpeckers because its social groups may permit better defense and more rapid construction of holes. Alternatively, however, its resident nature may limit flexibility in choice of nesting sites.