Navigating north: how body mass and winds shape avian flight behaviours across a North American migratory flyway

Abstract

The migratory patterns of birds have been the focus of ecologists for millennia. What behavioural traits underlie these remarkably consistent movements? Addressing this question is central to advancing our understanding of migratory flight strategies and requires the integration of information across levels of biological organisation, e.g. species to communities. Here, we combine species-specific observations from the eBird citizen-science database with observations aggregated from weather surveillance radars during spring migration in central North America. Our results confirm a core prediction of migration theory at an unprecedented national scale: body mass predicts variation in flight strategies across latitudes, with larger-bodied species flying faster and compensating more for wind drift. We also find evidence that migrants travelling northward earlier in the spring increasingly compensate for wind drift at higher latitudes. This integration of information across biological scales provides new insight into patterns and determinants of broad-scale flight strategies of migratory birds.

The grand challenges of migration ecology that radar aeroecology can help answer

“…An important step towards identifying important areas for migrants has been made by Buler and Dawson (), who used weather radar data from the eastern US to identify areas and habitats of high conservation value for large numbers of avian migrants. Radar data have also been combined with large scale citizen science data in the USA (eBird) for a detailed view of the bird migration strategies at the flyway level (Horton et al ) or with systematic entomological surveys in investigations of the migration circuit of the painted lady butterfly Vanessa cardui in the Western Palaearctic (Stefanescu et al ).…”

“…The biomass of aerial migrants that seasonally enter and leave a particular region could unravel patterns in recruitment (biomass gain) and mortality (biomass loss) (Chapman et al 2012, Hu et al ) and be linked to environmental variables that drive the variability in long‐term trends. Such information is critical for the early detection of population declines (Dokter et al ), and for installing timely remedial measures.…”

“…To reduce the risk of bird‐aircraft collisions, radar is being used in an operational capacity by military aviation in several countries for (near) real‐time monitoring of avian migration, and to develop migration forecast models used operationally (Shamoun‐Baranes et al , Van Gasteren et al ). Both are used to alter flight planning under high collision risk, saving money and lives.…”

“…A more complete understanding of how migrants respond to environmental change would be useful for predicting impacts of climate change on migration systems, and how these may carry over to communities and ecosystems. Many studies have documented changes in migration phenology associated with climate change (Carey , La Sorte et al ), yet large gaps remain in our understanding of migration phenology and its relationship to climate (Cohen et al ).…”

“…Migratory animals might be particularly affected as they rely on multiple, distant sites throughout their annual or life‐cycles (Runge et al , ) and changes in any of those sites are fitness‐relevant and may carry over to demographic rates and trends in their populations. There are also several evolutionarily novel factors such as artificial light at night (ALAN), electromagnetic noise, or wind energy installations, which have enormously expanded in recent years and now represent significant and ubiquitous distortions particularly to aerial migrations (Engels et al , Fijn et al , McLaren et al ).…”