Abstract
Every year, billions of birds undertake extensive migrations between breeding and non-breeding areas, facing challenges that require behavioural adjustments, particularly to flight timing and duration. Such adjustments in daily activity patterns and the influence of extrinsic factors (e.g., environmental conditions, moonlight) have received much more research attention in terrestrial than marine migrants. Taking advantage of the widespread deployment in recent decades of combined light-level geolocator-immersion loggers, we investigated diel organisation and influence of the moon on flight activities during the non-breeding season of 21 migrant seabird species from a wide taxonomic range (6 families, 3 orders). Migrant seabirds regularly stopped (to either feed or rest) during migration, unlike some terrestrial and wetland birds which fly non-stop. We found an overall increase for most seabird species in time in flight and, for several species, also in flight bout duration, during migration compared to when resident at the non-breeding grounds. Additionally, several nocturnal species spent more of the day in flight during migration than at non-breeding areas, and vice versa for diurnal species. Nocturnal time in flight tended to increase during full moon, both during migration and at the non-breeding grounds, depending on species. Our study provides an extensive overview of activity patterns of migrant seabirds, paving the way for further research on the underlying mechanisms and drivers.
Highlights
Every year, billions of birds migrate between breeding and non-breeding areas, often undertaking extensive journeys across unfavourable environments
We found some influence of the lunar phase on flight activity, but that was not necessarily more pronounced during migration than when birds were resident in their nonbreeding areas
For some species, we found an increase in flight bout duration during migration, which has been observed in albatrosses (Mackley et al, 2010)
Summary
Billions of birds migrate between breeding and non-breeding areas, often undertaking extensive journeys across unfavourable environments. Less constrained are birds crossing a region where they can stop to rest or to wait for better conditions, but in general cannot forage, such as the numerous passerines, raptors, and other species which migrate over the Sahara Desert (Klaassen et al, 2008; Strandberg et al, 2009; Lemke et al, 2013). Birds sometimes have to fly over moderately challenging barriers, i.e., areas where they can stop to rest and even find some food, but that are not suitable for long periods of residency; this applies to non-tropical seabirds migrating over equatorial oceans where marine productivity and wind speeds are consistently low (Mann and Lazier, 2005). The extent to which migrating birds must adapt their daily routines when crossing unfavourable habitats should depend on the ratio of energy accumulated while feeding to energy spent on travel (Strandberg and Alerstam, 2007)
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