Each spring, billions of birds embark on a risky journey from their overwintering habitats to their breeding grounds. Most Nearctic-Neotropical warbler species are nocturnal migrants with a short hop migration strategy, but little is known about their migratory flight duration each night. This study used radio-telemetry tags to track the flights of songbirds using the Motus Wildlife Tracking System (herein “Motus”), comprehensive network of automated radio receiver towers. During spring migration, Black-throated Blue Warblers (2014: n = 33; 2015: n = 21) and Magnolia Warblers (2014: n = 32; 2015: n = 69) were caught with mist nets and tagged with radio transmitters at the Long Point Bird Observatory (42.584°, −80.397°) before their release at the same site. The objective of this study was to estimate the nocturnal flight duration of these two species using a Cormack-Jolly-Seber mark-recapture model to estimate “survival” (the probability of remaining in flight) while accounting for imperfect detection. In addition, we tested whether favourable tailwinds extended flight duration.
Results/Conclusions
Preliminary model selection identified constant survival and time-dependent detection probability as the best model. After accounting for declining probability of detection as a function of time since departure, the hourly probability of remaining in flight was 0.58. This resulted in an estimated flight duration of 1.72 hours. Preliminary results also showed that favourable tailwinds extended flight duration, although the effect size was modest. There was also some evidence to support a decline in survival with time. These results were in line with our expectations that birds will be increasingly more likely to land with time since departure due to declining fuel reserves and the onset of dawn. The declining probability of detection is likely associated with a decrease in the coverage of towers found away from Long Point. Overall, the estimated flight duration seems low relative to the potential flight duration if birds were to fly all night. This study serves as the first attempt to quantify the nocturnal flight duration of songbird species in Ontario. In addition to further analyses, further work will be necessary to determine if short nocturnal flights are a general feature of warbler migration or whether it is context specific.
