Central-place foraging poses variable constraints year-round in a neotropical migrant

Background Central-place foragers are constrained in their habitat selection and foraging range by the frequency with which they need to return to a central place. For example, chick-rearing songbirds that must feed their offspring hourly might be expected to have smaller foraging ranges compared to non-breeding songbirds that return nightly to a roost. Methods We used GPS units to compare the foraging behaviour of an aerial insectivorous bird, the purple martin (Progne subis), during the breeding season in three regions across North America, as well as the non-breeding season in South America. Specifically, we tested foraging range size and habitat selection. Results Foraging range did not vary among regions during breeding (14.0 +/- 39.2 km(2)) and was larger during the nonbreeding period (8840 +/- 8150 km(2)). Purple martins strongly preferred aquatic habitats to other available habitats year-round and in the Amazon commuted from night roosts in low productivity sediment-poor water, where risk of predation was probably low, to daytime foraging sites in productive sediment-rich water sites. Conclusions We provide the first estimates for foraging range size in purple martins and demonstrate foraging preference for aquatic habitats throughout two stages of the annual cycle. Understanding foraging constraints and habitat of aerial insectivores may help plan conservation actions throughout their annual cycle. Future research should quantify foraging behaviour during the post-breeding period and during migration.

Automated summary

The study found that purple martins have smaller foraging ranges during the breeding season and larger ranges during the non-breeding season, consistently preferring aquatic habitats. Understanding foraging constraints and habitat preferences of aerial insectivores can aid in conservation planning. Further research on foraging behavior during post-breeding periods and migration is recommended.