Migratory birds with delayed spring departure migrate faster but pay the costs

Authors: Bryant C. Dossman, Amanda D. Rodewald, Colin E. Studds, Peter P. Marra

Year: 2023

Publication: Ecology

Publication Link: https://doi.org/10.1002/ecy.3938

Keywords: American redstart, automated telemetry, carry over effects, light-level geolocators, migratory delays, Motus, nonbreeding season, passerine, spring departure timing, survival

Abstract: Migratory birds that experience poor overwintering conditions are often late to
arrive at the breeding grounds, which is known to depress individual fitness.
Despite the importance of this carryover effect, few studies have investigated
how individuals can modify migratory behaviors en route to reduce delays on
arrival and whether accelerating migration incurs survival costs. To examine
this, we used Motus Wildlife Tracking System to track individual American
redstarts (Setophaga ruticilla) as they migrated from wintering grounds in
Southwest Jamaica through Florida en route to their breeding areas. We leveraged
long-term data on spring departure timing and breeding latitude to quantify
the relative departure dates (early vs. delayed) of tagged individuals, which
we then related to individual migration rates and apparent annual survival.
Compared to those initiating migration earlier, individuals that departed relatively
late (10-day delay) migrated at a 43% faster rate, which decreased their
annual survival by 6.3%. Our results are consistent with the hypothesis that
spring migrants use speed to compensate for departure delays despite incurring
survival costs. This compensatory behavior may potentially underly differential
survival during spring migration and may be particularly widespread
across short-lived migratory birds generally considered time-constrained.

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