Facultative polygamy may influence post-fledging movements in a brood-splitting passerine

Animal space-use patterns can vary widely with age, sex, and stage of the annual cycle, but the factors that drive pattern shifts are poorly understood. Here, we provide preliminary evidence that mating strategy (i.e., polygamy) influences movements of parents attending recently fledged young. We monitored the space use during the post-fledging period for Vermivora spp. broods led by a male and female with a split brood in 2014 and the same male with 2 fledglings in 2015. We observed context- and sex-specific space-use patterns that seemed to be driven by the male's attention to a secondary polygamous nest in 2014. When attending his secondary nest, the male restricted his primary brood's movements to within the nesting habitat close to his secondary nest until the nest failed. This pattern was distinct from movements of both the 2014 female and the same male in 2015 when he lacked a secondary nest. These observations may explain some reports from other studies that female-led broods disperse farther than male-led broods. Future work should explicitly consider the potential impacts of facultative polygamy on post-fledging space use, especially in species traditionally considered monogamous.