Advances in the modelling of bird populations has made it possible to assess the impact of climate change on two Mediterranean species of warbler, according to researchers in Valencia, Spain.

Data-mining, machine learning and genetic algorithms have all been used in the study, which concludes that more frequent torrential rains and warmer temperatures could compromise conservation of the moustached warbler and common reed warbler, both of which frequent Mediterranean wetlands.

The work by researchers at the Polytechnic University of Valencia and the Cavanilles Institute of Biodiversity & Evolutionary Biology at the University of Valencia has been published in Bird Study journal. It is part of a PhD thesis being undertaken by Pau Lucio, associate lecturer in the animal sciences.

The moustached warbler is a resident and short-distance migrant of Spain, listed as 'vulnerable' in the Spanish Red Data Book of Birds 2021, due to its population decline in recent years. The country is home to the largest population of this species in Western Europe.

In contrast, the common reed warbler has more generalist habitat preferences and is a long-distance migrant, visiting Spanish wetlands during the breeding season and wintering in Africa. Its conservation status is defined as being of 'least concern', as it is widely distributed throughout Europe.

According to Lucio, the research aims to understand the extent to which different climatic and geographical factors are affecting productivity, such as the relationship between the number of birds born in a given year and the number of adults of each species, using a large database with 25 years of ringing records from Spanish wetlands.

"Specifically, we have used data from the scientific ringing programme for the monitoring of breeding bird species in Spain (PASER) between 1995 and 2021." adds Lucio.

The study concludes that cumulative rainfall of up to 100mm favours the productivity of the moustached warbler, and rainfall above this threshold is detrimental to the reproduction of the species. As for temperatures, the team observed that hotter conditions have a negative effect.

In contrast, temperature positively affected common reed warbler productivity, while rainfall had almost no impact. However, productivity also peaked when rainfall was close to 100mm.

"Warmer temperatures and more frequent heavy rainfall may compromise the conservation of the moustached warbler in Spain due to the adverse effect of both elements on its productivity. In contrast, higher temperatures may benefit the common reed warbler," says Virginia Garófano of the UPV Gandia Campus.

Thus, the study concludes that, given the current climate emergency, it is likely that the population of the moustached warbler will decrease while the population of the common reed warbler could increase. However, further work is needed to establish the specific impact of climate change on survival and its implications for the population trends and dynamics of these two species.

The researchers say that one of the main advances of this work has been to be able to use a large database, with a large spatial and temporal distribution, and also to investigate the time window in which climatic variables have the most significant impact on productivity. This made it possible to define climatically sensitive periods, taking into account spatial variables such as site, longitude, latitude and elevation, and temporal changes.

"This advance in the ecological modelling of trends in bird populations has been possible thanks to the use of complex data modelling techniques such as data mining, machine learning techniques and the use of genetic algorithms in the optimisation of the models," says researcher Rafael Muñoz-Mas.