Atmospheric conditions create freeways, detours and tailbacks for migrating birds

Abstract

The extraordinary adaptations of birds to contend with atmospheric conditions during their migratory flights have captivated ecologists for decades. During the 21st century technological advances have sparked a revival of research into the influence of weather on migrating birds. Using biologging technology, flight behaviour is measured across entire flyways, weather radar networks quantify large-scale migratory fluxes, citizen scientists gather observations of migrant birds and mechanistic models are used to simulate migration in dynamic aerial environments. In this review, we first introduce the most relevant microscale, mesoscale and synoptic scale atmospheric phenomena from the point of view of a migrating bird. We then provide an overview of the individual responses of migrant birds (when, where and how to fly) in relation to these phenomena. We explore the cumulative impact of individual responses to weather during migration, and the consequences thereof for populations and migratory systems. In general, individual birds seem to have a much more flexible response to weather than previously thought, but we also note similarities in migratory behaviour across taxa. We propose various avenues for future research through which we expect to derive more fundamental insights into the influence of weather on the evolution of migratory behaviour and the life-history, population dynamics and species distributions of migrant birds.

Causes and consequences of facultative sea crossing in a soaring migrant

“…Still, how migration route is influenced by atmospheric and geographical factors is much less clear. Route selection over ecological barriers such as large waterbodies may depend on weather and geographical features (Alerstam, ; Becciu et al, ; Efrat, Hatzofe, & Nathan, ; Eisaguirre et al, ; Nourani, Yamaguchi, Manda, & Higuchi, ), affecting migration time and energy expenditures, with consequences for animal fitness (Shamoun‐Baranes, Bouten, & Van Loon, ; Shamoun‐Baranes et al, ). Large terrestrial soaring birds depend on local atmospheric conditions during their flight, since they utilize thermal uplifts to gain height and later glide towards their destination (Norberg, ).…”

Adverse wind conditions during northward Sahara crossings increase the in‐flight mortality of Black‐tailed Godwits

“…To explain why this variation exists, it is necessary to understand how it affects the reproductive performance and survival of individuals, as well as whether it is the result of ‘pre‐functional’ differences among individuals (Hogan ) or the result of different developmental trajectories (Piersma ). The large‐scale nature of migration has made developing this understanding difficult, especially when determining the mortality rates associated with different migratory strategies (Shamoun‐Baranes et al ). However, with the advent of miniaturised tracking devices and advanced survival analyses, we are now better able to study these associations in situ (Sillett & Holmes ; Strandberg et al ; Klaassen et al ; Lok et al ; Rockwell et al ; Ward et al ; Senner et al ).…”

Environmental effects on flying migrants revealed by radar

“…Inappropriate responses to environmental heterogeneity and dynamics could strongly jeopardize migrant fitness due to direct mortality or through carry-over effects that may lower reproductive output (Newton 2008). Although some important progress has been made in recent years (Krauel et al 2015, Shamoun-Baranes et al 2017, we still lack good understanding of how aerial migrants sense and respond to their dynamic habitat.…”