![]() 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. 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. ![]() 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). Specifically, we tested foraging range size and habitat more » selection. 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. 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. = ,īackground: “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. Future research should target how diel foraging and refueling strategies support nocturnal flights and barrier crossing in this and other diurnal species. Nocturnal flights at barrier crossing may provide time and energy savings where foraging opportunities are low in an otherwise diurnal strategy. Overall, our results demonstrate the use of nocturnal flight and a high degree of individual plasticity in migration strategies on a circadian scale in a species generally considered to be a diurnal migrant. Our results are consistent with diurnal birds using night flight to help achieve time- and energy-savings through ‘short cuts’ at barrier more » crossings, at times and locations when foraging opportunities are not available. Birds were not more likely to initiate crossings with supportive winds, however crossings were more likely when they reduced travel distances. 32% of all water crossings were initiated at night, demonstrating that night flight is not only used to complete large crossings but may confer other advantages for diurnal birds. Most (91%) of individuals made large (sometimes > 1000 km), open-water crossings of the Caribbean Sea and the Gulf of Mexico that included the use of night flight. We used high precision GPS tracking of a diurnal, migratory swallow, the purple martin (Progne subis), to determine whether individuals were flexible in their spring migration strategies to include some night flight, particularly at barrier crossing. However, individual plasticity in circadian patterns of migratory flights in diurnally migrating songbirds has never been investigated. ![]() Some species may show individual plasticity in the use of day or night flight, particularly when crossing large, open-water or desert barriers. The migration patterns of land birds can generally be divided into those species that migrate principally during the day and those that migrate during the night. ![]()
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