Does Breeding Density Covary with Extra-Pair Fertilizations in Hooded Warblers?

Abstract

The extent of variation in the frequency of extra-pair matings among and within avian species could result from differences in breeding density, where breeding density is predicted to be positively correlated with extra-pair paternity. We combined paternity data and behavioural observations to evaluate this prediction using correlational data in relation to observed densities of Hooded Warblers Wilsonia citrina by comparing populations differing in (1) nearest neighbour distance which varied by more than an order of magnitude (range 50-600 m) and (2) the number of adjacent neighbours within 300 m (range 0-8). Spearman rank correlations demonstrated no relationship between extra-pair paternity and either inter-territory distance or the number of adjacent neighbours within 300 m. The rate of extra-territorial forays, female chip rates, the number of chipping bouts, time spent chipping, male song rates, the number of song bouts and time spent singing were similar among pairs breeding at different densities. Our results suggest that a simple linear relationship between density and extra-pair paternity may not exist in some avian species, possibly because the costs of inter-territory travel may be much lower than the benefits gained through extra-pair fertilizations, and also because of the conflicting mating tactics used by males and females.