European birds with narrow climate tolerance face population declines

New research suggests conservation efforts could more effectively identify and protect bird species at greatest risk from climate change by better understanding the range of specific conditions they need to thrive.

The study, led by the University of East Anglia (UEA), examined the relationship between the extent of the climatic conditions that species tolerate and in which populations can survive—known as climatic niche breadth—and their likelihood of declining in response to climate change.

For species inhabiting a similar area of geographic space, those able to tolerate a wider range of climate conditions are less likely to experience population declines, and are more likely to be increasing, compared to those with narrower climatic preferences.

The authors say their findings, published in the Journal of Biogeography, provide valuable insights into how climatic niche breadth can act as an important factor in predicting bird species’ vulnerability to climate change. The paper is titled “European breeding bird declines associated with narrower climatic niches.”

They suggest incorporating species’ climatic niches into climate change risk assessments to better inform conservation strategies, arguing that variation in climatic conditions within a species’ range can provide greater nuance in understanding their resilience to factors that affect their population.

“Deciding which species are more at risk isn’t straightforward, and species may be declining for a range of reasons,” said lead author Karolina Zalewska, a postgraduate researcher in UEA’s School of Environmental Sciences.

“Rare species and those that have smaller distributions are more likely to be vulnerable to climate change. This study has shown that birds that are more widespread, such as the house sparrow and the common starling, can also face threats to their populations.

“Species, whether rare or widespread, with narrower climatic niches may be more susceptible to the rapid changes brought on by climate change compared to those with broader niches, and this may be one of the underlying reasons behind the population declines observed.

“Our results emphasize the importance of understanding and incorporating the level of exposure to climatic variability when assessing vulnerability to climate change and long-term population declines.”

Human-induced climate change has increasingly been identified as a major threat to global biodiversity. However, the extent of this threat is likely to be uneven across species, due to differences in life histories or exposure to environmental change, with some climatic conditions, such as variables of temperature and rainfall, being more widespread than others across geographic area.

While species with broad geographic distributions would be expected to experience a wider range of climatic conditions and so be more resilient to environmental change, recent population declines of many widespread species suggest other factors may be involved, with the breadth of climatic conditions a species experiences being a possible indicator of their resilience to climate change.

Co-author Prof Aldina Franco, also from the School of Environmental Sciences, said, “Faced with the challenges of the global biodiversity crisis and climate change, the rapid assessment of species’ vulnerability to environmental change has become of paramount importance to address priorities for conservation.

“As climate change accelerates, our study highlights the need to prioritize species that are most at risk due to their more restricted environmental requirements.”

The researchers drew on data for the population trends of 159 European breeding bird species across 29 European countries from the Pan-European Common Bird Monitoring Scheme. These 40-year population trends were related to the climate conditions species experience and their distribution area.

They used 30 years of climate data for the species breeding ranges to construct representations of their climatic niches and produced a new index of climatic niche breadth that accounts for species distribution area.

This analysis, along with additional factors such as the species’ diet, primary habitat type, migratory status, and average body mass, was then used to explore how these variables influence the long-term population trends.

“These findings can help us understand the threats associated with climate change and allow for rapid assessment of the importance of climatic factors on population trends, providing an invaluable tool for targeting species conservation,” added Miss Zalewska.

“In particular, we show that the climatic niche breadth to range area index can help predict which species may be more vulnerable to population declines.”

Within the species included in this study, 58 had a decreasing population trend, populations of 68 species were stable and 33 were increasing.

As in previous studies, the team found that species associated with farmland habitats, both in the UK and wider European area, such as the corn bunting or skylark, were more likely to be declining, while those able to tolerate human-modified environments, including blackbirds and blue tits, were more likely to experience increasing population trends.