Does urbanization influence population trends of cavity-nesting birds and their relationship with European starlings?

Abstract

European starlings (Sturnus vulgaris) in North America often achieve high densities in urban regions and compete with other cavity-nesting species for nest sites, including the rapidly declining red-headed woodpecker (Melanerpes erythrocephalus). However, at a continental scale, European starling populations are unrelated to trends in red-headed woodpeckers. To assess whether urbanization influences population trends of cavity-nesting bird species and the relationship between European starlings and other cavity-nesting birds, we compared population patterns within the highly urbanized region of Cook County, Illinois, USA (which encompasses the city of Chicago) with data from surrounding rural counties. We used data from the Breeding Bird Survey (BBS) and the Christmas Bird Count (CBC) spanning 1970–2017, and i) quantified population trends of 19 cavity-nesting species, and ii) examined the patterns of relationships of each of these species with European starlings. Models fit to population trends over time with a variable for urban/rural location included were selected over models without urban/rural location for 14/17 species in the BBS and 14/15 species in the CBC. Starlings showed population declines in both urban and rural BBS and in urban CBC, while they increased in the rural CBC. Red-headed woodpecker populations declined across every survey set and location. Contrary to predictions, the counts of some species in surveys were significantly positively correlated with European starling population trends, while none were significantly negatively correlated. Our findings suggest that urban and rural locations add information to population trends of cavity-nesting species, and that European starlings have little negative impact on cavity-nesting birds in either rural or urban locations, suggesting that habitat loss and other factors are likely greater impacts on red-headed woodpeckers and other members of the cavity-nesting guild.