Why do birds migrate? A macroecological perspective

Abstract

Aim Bird migration poses a challenge to macroecology, because with one in five species moving twice yearly between breeding and non-breeding grounds, macroecological patterns in birds are dynamic rather than static. But migration is also a natural experiment for testing hypotheses about the ecological mechanisms driving species distributions. Here, we use macroecological patterns of migratory bird diversity to test whether seasonality, winter harshness and the cost of migration drive the global distribution of migratory birds. Location Global.Methods We used data on the distribution of the world's bird species to derive global empirical patterns of: the number of breeding migrants, the number of non-breeding migrants and the difference in seasonal diversity. We built statistical models with ecologically meaningful predictors related to each of the hypotheses and investigated if they can significantly explain global empirical patterns of migratory bird diversity. We formally tested these models by training on one hemisphere (Western or Eastern) to predict the other hemisphere in turn. Model predictions were assessed in terms of match to the empirical data and their ability to predict the spatial features of patterns. ResultsWe found strong support for the hypotheses that birds move to breeding grounds to exploit a surplus in resources, preferring areas with harsh winters (presumably to avoid competition). In contrast, distribution during the nonbreeding season seems driven by avoidance of harsh winters and connectivity to breeding grounds. Models integrating these hypotheses explain well the observed variance in the empirical patterns and reproduce key spatial features, even when models trained in one hemisphere are used to predict another. Main conclusionsThe strong predictive power of the models suggests that we have captured the main mechanisms that drive global patterns in bird migration. The fact that the models perform well despite being applied to species with very different ecologies suggests general mechanisms driving migration across taxa.

Shifts in Bird Migration Timing in North American Long-Distance and Short-Distance Migrants Are Associated with Climate Change

“…Additionally, the departure date and the number of days that they stayed in their summer or wintering residence were most influenced by maximum temperature (Table 3). These results support the previous notion that birds may migrate to winter locations to avoid harsh (cold) temperatures in their breeding grounds [41][42][43][44]. As the maximum temperature during the winter increases, birds might then return back to their breeding grounds.…”

Fitness consequences of different migratory strategies in partially migratory populations: A multi‐taxa meta‐analysis

“…Taxonomic biases, particularly the ornithocentrism in animal migration literature found elsewhere (Bauer et al, ), are partly a result of migratory behaviour being more common in certain groups and partly a reflection of feasibility: species more readily tracked and monitored are more likely to be the subject of studies relevant to this topic. Similarly, while the prevalence in this study of data from the Northern Hemisphere is in part a product of a more general bias found across ecological literature (Amano & Sutherland, ; Martin, Blossey, & Ellis, ), there is also greater prevalence of terrestrial migratory species in the Northern Hemisphere due to a combination of high seasonal variability and greater land mass (Somveille, Rodrigues, & Manica, ).…”

Reconstructing the geographic and climatic origins of long‐distance bird migrations

“…A largely documented biogeographic pattern is the tendency of most migratory birds to breed in regions characterized by strongly seasonal environments (Somveille, Rodrigues, et al, 2015. A recent paper (Winger, Auteri, Pegan, & Weeks, 2019) reviewed the studies that attempted to integrate theories about the evolution of bird migration with the biogeographic history of migratory clades (Louchart, 2008;Salewski & Bruderer, 2007;Winger, Barker, & Ree, 2014;Zink, 2002) and stressed that the biogeographic origins of bird migration have rarely been considered in relation to the onset of climatic seasonality.…”