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

Abstract

A 6-yr study was conducted to determine if competition with starlings [Sturnus vulgaris] for tree holes is affecting breeding strategy or fecundity of the acorn woodpeckers [Melanerpes formicivorus] in California [USA]. The pattern of starling visitation to acorn woodpecker territories did not vary during 6 yr, but the number of their summer and fall hole visits increased. Starlings were effective competitors for acorn woodpecker holes, and the number of individuals breeding increased during the study. The acorn woodpecker groups responded to hole loss by excavating more holes and using various methods that allowed successful breeding. Thus, their fecundity seemed not to have been affected by starling hole competition, and the local population remained stable. However, their habitat preferences are such that intense starling hole competition will continue and spread throughout their range. Increased need for hole defense or lack of nest trees may limit acorn woodpecker breeding. A number of red-shafted flicker[Colaptes auratus cafer]-starling habitat preferences were analyzed. In the future, successfully breeding red-shafted flickers may be found primarily in high mountains and forests.