A European roller (Coracias garrulus) perched on a branch. / Photo: Manuel Gómez, EBD-CSIC

In a context of global warming that is intensifying extreme weather events, the ability of species to adapt to environmental changes is key to ensuring their survival. A study led by the Estación Experimental de Zonas Áridas (EEZA-CSIC), with the participation of the Estación Biológica de Doñana (EBD-CSIC), has analyzed how the European roller (Coracias garrulus)—a migratory bird that normally lays only one clutch of eggs per year—adjusts its breeding in response to episodes of extreme rainfall. The study was published in the scientific journal Journal of Avian Biology.

The research documents how in 2023, a year marked by extreme rainfall in the arid region of Tabernas (Almería), the European roller experienced a sharp increase in failed breeding attempts. In response, the birds increased the number of replacement clutches (new batches of eggs laid after the loss of a previous clutch) to levels never recorded in the 18 years of monitoring. In addition, the breeding season lengthened: egg-laying began about five days earlier than usual, and the final clutches were delayed by up to 11 days.

Despite this, Francisco Castaño Vázquez, researcher at the EEZA-CSIC and co-author of the study, notes that the number of chicks and overall breeding success did not differ from the average of the past 18 years, highlighting the species’ reproductive flexibility.

This quasi-natural experiment revealed significant shifts in reproductive phenology—that is, the timing of breeding—as well as a high rate of failed breeding attempts during the incubation stage. The European roller typically produces a single clutch per year and only rarely lays a second if the first fails. However, in 2023 researchers detected an “unprecedented” increase in compensatory breeding attempts. According to Radovan Václav, co-author of the study and scientist at the Institute of Zoology of the Slovak Academy of Sciences, the research provides “valuable information on how birds respond to climate change.”

The 11-day delay in egg-laying at the end of the breeding season may pose an additional risk, as summer heatwaves usually reduce the abundance of insects that rollers feed on and increase the exposure of chicks to heat stress. This response to heavy rainfall “could compromise the future survival and reproductive success of both adults and their late-hatched offspring,” says Francisco Valera, EEZA-CSIC researcher and senior author of the study.

Roller chicks showed higher survival rates in nest boxes and in natural cavities, whereas nests in human constructions were particularly vulnerable to heavy rainfall. Jesús Veiga, researcher at EBD-CSIC and co-author of the study, stresses the importance of long-term monitoring and of properly designing nest boxes “to mitigate the challenges posed by climate change,” as well as planning conservation strategies that take climate-driven shifts in breeding timing into account.

This research is the result of a collaboration between two CSIC centers (the Estación Experimental de Zonas Áridas and the Estación Biológica de Doñana), the Complutense University of Madrid, and the Institute of Zoology of the Slovak Academy of Sciences. The study was funded by the Slovak Ministry of Education, the Spanish Ministry of Science, Innovation and Universities, and the European Union.

Content produced by Fermín Grodira within the CSIC–BBVA Foundation Science Communication Grants Program, 2024 Call.

Reference

Radovan Václav, Francisco Castaño-Vázquez, Jesús Veiga, Francisco Valera. (2026). Reproductive flexibility in a single-brooded migrant: can the European roller Coracias garrulus adapt to extreme weather events? Journal of Avian Biology. https://doi.org/10.1002/jav.03502