Climate decoupling is an increasing threat to birds

Climate change poses a number of threats to plants and animals, and many species may disappear altogether. This is only expected to worsen due to human impacts such as altering land use for agriculture. 

The habitats and preferred climate conditions of species have been drastically impacted. When there is a divergence between the climatic conditions suitable for a particular species and its abundance and distribution through time, this is known as climate decoupling. 

For example, the grasshopper sparrow lives in grasslands across North America. However, because grasslands continue to be degraded, this has hindered the species from fully adjusting to changing climatic conditions. Climate decoupling and habitat loss may explain the high rates of grasshopper sparrow abundance declines and local extinctions.

A team of researchers led by iDiv, Leipzig University and MLU used the best available evidence on bird population changes through time from the North American Breeding Bird Survey (BBS).

The study revealed that at least 30 out of 114 species (26 percent) of North American birds have become less adjusted to their climate over the last 30 years. This means that their distributions and abundances were increasingly decoupled from climate over time. 

This can happen for various reasons, depending on the species. Some species might remain where they historically lived, while others might be limited by climate-independent resources and habitats. On the other hand, some species might be declining due to global changes, unable to adjust to the changing climate. 

“One of the most surprising results of our analysis was that the overall trend of climate decoupling showed no signs of slowing down,” said lead author Dr. Duarte Viana. “This suggests a possible feedback between climate decoupling and declining populations that might emerge in the face of a multitude of current global changes.”

The researchers showed that climate decoupling was more prevalent among habitat specialists than generalists. This is because specialists may have greater difficulty finding a suitable habitat and climate conditions in increasingly modified landscapes.

“We also found that climate decoupling was more prominent among species that were considered threatened and that were declining in population sizes,” said study senior author Dr. Jonathan Chase, head of the Biodiversity Synthesis research group at iDiv and MLU. 

“There are many known factors that are contributing to the population declines of many species of birds, but our study adds a new facet to our understanding of the potential causes of some of these changes – that species are less likely to be living in their optimal climate conditions as the world changes around them. This, like the proverbial canary in the coal mine, might be something we humans should pay attention to as we will likely soon find ourselves similarly living in places outside of our optimal climate ranges.”

The study is published in the journal Nature Ecology & Evolution.

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By Katherine Bucko, Earth.com Staff Writer