Interspecific competition and nest survival of the threatened Red-headed Woodpecker

Abstract

The cavity-nesting Red-headed Woodpecker (Melanerpes erythrocephalus) is a once common, but now threatened, species across most of its range. Although several drivers for the species’ decline have been suggested, few have been quantitatively tested and still little is known of the Red-headed Woodpecker’s breeding ecology. From 2010 to 2011, we monitored 60 Red-headed Woodpecker nests across a variety of habitats in southern Ontario to estimate the species’ nest survival near the northern edge of their range where populations are rapidly declining. We investigated the relevance of a suite of meteorological, biotic, temporal, and habitat-based drivers on woodpecker nesting success. The frequency of European Starlings (Sturnus vulgaris) sightings near active woodpecker nest sites was the strongest factor influencing Red-headed Woodpecker nest survival. Logistic-exposure nest success assuming constant survival (68 %) dropped significantly (to 13 %) when the frequency of Starling sightings was considered. More than a third of nest failures were suspected to be the result of aggressive cavity takeovers by Starlings, and nests with Starlings present were almost four times more likely to fail than nests without. Red-headed Woodpecker nest survival early in the breeding season appeared depressed, perhaps as a result of interference competition with Starlings. Nesting success increased with the availability of snags and dead branches, which may increase foraging opportunities and parental attentiveness at the nest, leading to more effective nest defense. This research is contrary to previous reports that Starlings do not negatively affect North American primary cavity nesters, and demonstrates the importance of considering multiple ecological, temporal, and spatial factors when determining threats for species-at-risk.