COS 81-2 - Influence of the lunar cycle on individual migration movements and timing in a nocturnal bird, Eastern Whip-poor-will (Antrostomus vociferus)
Consistency in annual, seasonal, or diel movements allows animals to structure their use of space and time to predictably find resources and mates, maintain territories, and avoid predators. Migrating birds may improve fitness by reusing familiar routes and stopover sites, and by timing departures and arrivals to coincide with relatively predictable resources. For example, some nightjar species forage most effectively on nocturnal aerial insect prey during periods of bright moonlight, and this lunar-driven foraging behaviour may influence departure and stopover timing during migration. Moon cycle dates differ from year to year, providing a potential temporal conflict or mismatch for individuals that may benefit from maintaining consistent annual schedules, but could optimize foraging by matching their timing to external moonlight cues. Repeat annual tracking allows us to quantify behavioural variation both within and among individuals in relation to varying ecological conditions. We GPS-tracked the fall migrations of 40 Eastern Whip-poor-wills (Antrostomus vociferus) between breeding grounds in Canada and wintering grounds in Mexico and Central America over successive years, to investigate the relative contributions of the lunar cycle and individual consistency to migration timing and routes.
Results/Conclusions
We collected 62 migration tracks from 40 Whip-poor-wills, and 48 fall migration departure dates from 38 birds. We observed relatively high individual consistency in fall departure dates and wintering ground arrival dates, despite inter-annual variation in timing related to moon phase. All migrations (durations ranged from 17 to 64 days long) included at least one full moon phase, and stopovers lasting more than one day occurred most frequently during periods of high moon illumination. We found no evidence of individual fidelity to specific stopover sites, suggesting that there is flexibility in migration route decisions. Our results reveal plasticity in migratory phenology and stopover site selection in response to lunar synchrony, and illustrate how individual consistency in migratory timing may constrain the ability to respond to environmental change.
