Extrapair paternity in a far northern population of yellow warblers (Dendroica petechia)

The proportion of extrapair paternity is known to vary greatly among species, but differences between populations of the same species have rarely been considered. We used microsatellite DNA markers to assess parentage of offspring in a subarctic population of the socially monogamous Yellow Warbler Dendroica petechia nesting near Churchill, Manitoba. We found a significantly lower proportion of extrapair young in the Churchill population than in a temperate population nesting approximately 1500 km to the south near the Queen's University Biological Station (QUBS) in Ontario. We show that the Churchill population also had significantly lower nesting density and significantly higher breeding synchrony; both are factors that have been hypothesized to affect extrapair paternity negatively. We suggest that inter-population comparisons can be used to test proximate mechanisms affecting extrapair paternity and in some cases may be better than interspecific or inter-individual comparisons. Towards this end we list eight other species that have had extrapair paternity measured in different populations.