Dynamics of Woodpecker – Common Starling interactions: a comparison of Old World and New World species and populations

Woodpecker species whose cavities are most usurped by Common Starlings (Sturnus vulgaris) are widespread and generalists in their use of habitats. These include primarily woodpeckers that are similar in size to or slightly larger than the starling - such as the Great-spotted Woodpecker (Dendrocopos major) of Eurasia and the Northern Flicker (Colaptes auratus) and Red-bellied (Melanerpes carolinus) and Red-headed (M. erythrocephalus) Woodpeckers of North America. Usurpation occurs primarily in human-dominated urban, suburban and exurban habitats with pastures, sports fields and other open areas that serve as prime feeding habitats for starlings. Starlings prefer high, more exposed cavities with a minimal entrance diameter relative to their body size. Usurpation success depends on timing - optimally just as a cavity is completed and before egg-laying by the woodpeckers. Starlings likely reduce woodpecker populations in more open, human-dominated habitats. Woodpecker habitat losses and fragmentation are more serious problems that enhance habitat quality for starlings and reduce habitat quality for most woodpeckers. The only woodpeckers that might become in danger of extinction as a primary result of starling cavity usurpation are likely island species with small populations. Conservation of rare species limited to islands, such as Fernandina’s Flicker (Colaptes fernandinae) of Cuba, may depend on our ability to prevent the establishment of the Common Starling or other aggressive cavity competitors on their island.

Understanding and interpreting impacts of woodpecker cavity usurpation must include consideration of past woodpecker and Common Starling population fluctuations, breadth of habitats used by woodpecker species, and habitat limitations of Common Starlings. Conservation efforts for woodpeckers and other primary and secondary cavity-nesting species must focus on changes in tree, forest and ecosystem management to encourage maintenance of dead wood, large contiguous tracts that include diverse tree species and old growth, and forested linkages among such areas.