Productivity as the main factor correlating with migratory behaviour in the evolutionary history of warblers

Abstract

The evolution of migration in birds and its causes are still subject of debate. Recent studies tracking current bird migration have identified peaks in net primary productivity (NPP) as a main driver of bird migratory behaviour. However, it is unclear which variables may have played a major role in the evolution of bird migration at deeper phylogenetic levels. Here, we used phylogenetic comparative methods to assess whether the evolutionary patterns of migratory distances, as a proxy for migratory behaviour, are correlated with several biometric, climatic and productivity variables in a phylogenetic context, using Sylvia warblers as a case study. Our results recover NPP in the breeding range and during the breeding season as the variable with stronger positive correlation with migratory distances, being always included in the best models considering all potential variables. Several climatic variables show a correlation with the evolution of migration, but those are also tightly correlated with NPP. Among morphological variables, migratory lineages tend to have longer wings than sedentary ones. Although NPP has been identified as a driver of migratory behaviour in current species, in a phylogenetic scale it is not possible to disentangle if it was a main driver in the evolution of bird migratory behaviour or a consequence of it, yet migration and NPP seem to be tightly related today and along the long evolutionary history of these passerines.

Seasonal climatic niches diverge in migratory birds

“…Several drivers have been proposed to explain the origin of bird migrations, including competition avoidance (Cox 1968), reduced parasitism (Piersma 1997) or lower predation risk (McKinnon et al 2010). However, the main driver of such long journeys may be related to the availability of energy surplus as food, particularly in breeding ranges, as has been shown in other studies (Somveille et al 2015, Ponti et al 2018. It is likely that long-range migratory species move from breeding to non-breeding areas to profit from the peaks of net primary productivity in each season, showing enough plasticity and physiological breadth to abide different climatic conditions between breeding and non-breeding periods.…”

“…, Ponti et al . ). It is likely that long‐range migratory species move from breeding to non‐breeding areas to profit from the peaks of net primary productivity in each season, showing enough plasticity and physiological breadth to abide different climatic conditions between breeding and non‐breeding periods.…”

“…, Ponti et al . ; see Table S3). We calculated the niche overlap between breeding ranges or non‐breeding ranges of those species pairs, using the same methodology described above.…”

“…We did not perform phylogenetic analyses given the lack of genetic information for many migratory species from Africa and Europe. We selected all sister species present in our dataset, or species that were phylogenetically closely related, and also some trios when the relationship between phylogenetically closely related species was not clear, based on different phylogenetic hypotheses (Riesing et al 2003, Alstr€ om et al 2008, Aliabadian et al 2007, Gonzalez et al 2009, Gibson & Baker 2012, P€ ackert et al 2012, Arbabi et al 2014, Dos Remedios et al 2015, Oatley et al 2015, Tietze et al 2015, Ponti et al 2018; see Table S3). We calculated the niche overlap between breeding ranges or non-breeding ranges of those species pairs, using the same methodology described above.…”

“…breeding vs. nonbreeding) because, in each period, migratory birds have different environmental requirements, e.g. a surplus of energy in terms of food in the breeding ranges (Somveille et al 2015, Ponti et al 2018 or moulting during the non-breeding season or at the end of the breeding season (Svensson and Hedenstrom 1999). In this context, we wanted to test different possible hypotheses.…”