Drought and torrential rains are the biggest climate threat to birds in the Mediterranean

Storm Filomena covered Spain with extreme snowfall in a matter of days and, in addition to the impact it had on the population, scientific studies have found that birds such as the red partridge ( Alectoris rufa ) and the short-billed lark ( Chersophilus duponti ) suffered a major decline. Now, research recently published in the scientific journal Oikos and signed by several entities in Catalonia, including CREAF and ICO, has analyzed the impact of extreme climate episodes on the population of European birds over 20 years and shows, for the first time, that drought and torrential rains are the climatic variables that cause the greatest decline in the population of birds in the Mediterranean basin. In addition, they have also found that the negative impact of heavy rains is not limited to this territory, but causes a decline in birds throughout Europe.

Among the reasons that can explain this impact, the authors point out that drought increases the mortality of insects, such as butterfly caterpillars, and causes plants to grow less and produce fewer fruits and seeds . This has a cascading effect, because birds have less food to give their chicks, which need a lot of protein, and the survival rate drops. In the case of intense rains - increasingly frequent in the Mediterranean - they break nests, can cause the loss of eggs or the death of chicks from cooling and, in extreme situations such as hailstorms, can also injure adults.

In the case of the Mediterranean, the fact that there are fewer birds may reduce the key functions they perform "such as dispersing seeds or controlling insect pests," adds Herrando, co-author of the study.

Another finding has been that the increase in temperature favours birds that live permanently in northern Europe , probably because there is a longer period favorable for breeding. On the other hand, it harms long-distance migrants that arrive north in the spring , because the life cycle of plants and insects is desynchronized and when they arrive there is not as much food. “A case that has been demonstrated in other research is that of the mastigatxes ( Ficedula hypoleuca ), which when it arrives from Africa is found that the caterpillar cycle has advanced and there are no longer as many”, highlights Herrando.

To carry out the research, the research team has analysed 20 years of evolution (2002–2022) of bird populations in three major climatic regions of Europe - Mediterranean, continental and boreal -, using Catalonia, the Czech Republic and Sweden as representative territories. "In Catalonia, data from the ICO's Monitoring of Common Birds (SOCC) have been key to reaching these conclusions", he adds. In total, the population dynamics of 141 bird species from various habitats - forest, grassland, agricultural and urban - have been studied , and include both resident and short- and long-distance migratory species. These data have been crossed with annual data on three climatic variables: temperature, water availability and episodes of intense rainfall .

According to the team, a simple measure to help birds in the Mediterranean region during droughts is to restore the network of small ponds and water points in general, or build new ones . These ponds can have a direct beneficial effect because thirsty birds can drink, and also an indirect one, because they can attract insects. However, they warn that their installation must avoid areas of predation , especially by domestic cats. “Ponds can also be very beneficial for other animal species, such as amphibians,” adds Herrando.

The work has been led by Charles University in Prague and the Czech Academy in Prague, and is also signed by an international consortium of scientists linked to universities and research centers in Spain, the Czech Republic and Sweden, including the CSIC and the Catalan institutions Forest Science and Technology Center of Catalonia (CTFC), CREAF and the Catalan Institute of Ornithology, as well as the Palacký University of Olomouc and the University of Lund.

CREAF also included Lluis Brotons, also a researcher at the CSIC and the CTFC. The authors conclude by highlighting that the study “is one of the most complete assessments made to date on how climate conditions the dynamics of bird populations in Europe and will allow us to better refine conservation strategies .”

Scientific reference: Hanzelka, J., Telenský, T., Brotons, L., Herrando, S., Lindström, Å. & Reif, J. (2025). Latitude-specific responses of European birds' population growth rates to temperature and water availability. Oikos, 2025: e11460. https://doi.org/10.1002/oik.11460