Combined roles for breeding synchrony, habitat and scale as predictors of extrapair paternity

Abstract

Despite extensive research on passerine reproduction, it remains difficult to predict which traits of individuals, nesting populations and landscapes drive extrapair paternity (EPP). Two broad categories of drivers, habitat structure and population level factors, have been considered separately or at a single spatial or temporal scale. We used a 6-year nesting data set of scissor-tailed flycatcher, Tyrannus forficatus , which have high rates of cuckoldry (73% of nests, 59% of nestlings), to explore how nest density, breeding synchrony, habitat structure and clutch initiation date affect EPP rates. We further considered synchrony at two temporal and habitat structure at two spatial scales. We predicted that visual occlusion from vertical habitat structuring on breeding territories would allow extrapair males to go unnoticed and provide cover for extrapair copulations. Predictions for effects of nest density and fertility synchrony were double-edged: EPP may either increase as extrapair mate availability and ease of comparison with social mates increases or decrease as social mates increase their efforts to assure paternity. Using Bayesian techniques, we found a combination of population level factors and habitat structure, including interactions among the latter, at different scales best accounted for variation in EPP. EPP declined with increasing population synchrony. Variation in EPP was also explained by fine-scale habitat measures, decreasing with increasing nest tree diameter at breast height and woody vegetation cover but increasing with tree density. Notably, EPP increased with a coarse-scale habitat measure, linear extent of fence or powerline, suggesting a role for human alteration of habitat. Fences are used as communal perches by neighbours and floater males, potentially increasing interactions between asynchronous individuals. Our study demonstrates that breeding synchrony influences the probability of EPP and that habitat structure on individual territories is a strong predictor of paternity that acts independently of breeding density or synchrony at our scale of measurement. • We explore factors influencing cuckoldry in scissor-tailed flycatchers across 6 years. • Cuckoldry increased with populationwide fertility synchrony. • Cuckoldry was not related to spatial distribution of nests. • Cuckoldry increased with tree number and powerline/fence length and low shrub cover. • These correlates may impact cuckoldry via their effects on male mate guarding.