Researchers analyzing the changing abundances of birds in the U.S. and Europe reveal that climate change impacts bird populations in both good ways and bad – but at least the patterns are predictable. The findings were published in Science this week. 

Changes in climate can cause diverging effects on wildlife populations: They can decline, increase, or remain steady. For example, populations of white-throated sparrows (pictured above) have been declining throughout their breeding range in the northeast U.S. Meanwhile, wrens (pictured below to the right) have been increasing in parts of northern Europe where the winters are becoming more and more mild – but they’re declining in southern countries where summers have been getting both hotter and drier.

A large international team led by Durham University’s Stephen Willis studied data on the abundance of 145 bird species in Europe and 380 species in North America collected from 1980 to 2010. They divided the birds into two categories: those enjoying an increasingly suitable climate and those whose climate suitability has been declining over the last three decades. 

Climate change, they found, is predictably impacting population sizes across the two Northern Hemisphere continents. Species likely to benefit from increasing temperatures and subsequent effects tended to increase in abundance, while populations expected to do badly were indeed negatively impacted.

This consistency across North America and Europe suggests that their so-called "climate impact indicator" approach can be applied to other areas that have long-term monitoring data – though these are less available in the tropics, subtropics, and the Southern Hemisphere.

"These findings represent a new climate impact indicator for biodiversity. The same approach could also be applied to species such as bees, butterflies and dragonflies, which are well monitored and highly susceptible to changes in climate," Willis said in a statement. "This helps us to understand where climate change is affecting populations, and to understand the causes of population changes of common birds that might also be affected by factors such as habitat loss and agricultural intensification."

^{The American robin is declining in southern states including Mississippi and Louisiana, but increasing in northern central states, such as the Dakotas. U.S. Fish & Wildlife Service}

^{Image in the text: Wren. Stephen Willis/Durham University}