Some bird species in North America have not fully adjusted their distributions in response to ongoing climate change. The habitats of these birds have become increasingly disconnected from their optimal climate conditions, while other aspects of the environment have become more constraining. This trend of climate decoupling is more pronounced for habitat specialists and species in decline.
The findings were published in Nature Ecology & Evolution by the German Centre for Integrative Biodiversity Research (iDiv), Leipzig University, Martin Luther University Halle-Wittenberg (MLU), and the Doana Biological Station. Climate decoupling as a result of ongoing climate change may put additional strain on many bird species and exacerbate population declines.
Plants and animals face a number of challenges as a result of climate change. For example, as the climate changes, many species’ appropriate climatic conditions change, and some may disappear entirely. This is likely to worsen as the climate changes in tandem with other human-caused changes, such as land use for agriculture or other purposes. Climate decoupling occurs when there is an increasing divergence between the climatic conditions suitable for a particular species and its abundance and distribution over time.
One of the most surprising results of our analysis was that the overall trend of climate decoupling showed no signs of slowing down. This suggests a possible feedback between climate decoupling and declining populations that might emerge in the face of a multitude of current global changes.
Dr. Duarte Viana
The grasshopper sparrow (Ammodramus savannarum), for example, lives in grasslands across North America and was once quite common there. However, because grasslands are being degraded or lost, this grassland specialist species has been unable to fully adapt to changing climatic conditions. Climate decoupling, in conjunction with habitat loss, may explain the observed rapid declines in grasshopper sparrow abundance and local extinctions.
It is not only the grasshopper sparrow that is decoupling from its optimal climate conditions. 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) and found that at least 30 out of 114 species (26%) of North American birds have become less well adjusted to their climate over the last 30 years. This means that their distributions and abundances were increasingly decoupled from climate over time.
The reasons may differ depending on the species. Some species may prefer to stay in areas where they have previously lived. Climate-independent resources and habitats may limit some species. Furthermore, some species may be declining as a result of global warming and thus unable to adapt to changing climate. Approximately 10% of the species studied had positive temporal trends in climate matching, indicating that they became more coupled to climate over time. There was less support for significant temporal trends in climate matching for the remaining species, implying that their abundances and distributions remained more stable over time.
“One of the most surprising results of our analysis was that the overall trend of climate decoupling showed no signs of slowing down,” says lead author Dr. Duarte Viana, who did most of this study while working at iDiv and Leipzig University and is now based at the Doñana Biological Station in Seville. “This suggests a possible feedback between climate decoupling and declining populations that might emerge in the face of a multitude of current global changes,” he adds.
Climate decoupling was found to be more common among habitat specialists than among generalists, according to the researchers. In increasingly altered landscapes, these specialists may have a more difficult time finding the right combinations of suitable habitat and climate conditions.
“We also discovered that climate decoupling was more prevalent among threatened species with declining population sizes,” says senior author Prof Dr. Jonathan Chase, head of the Biodiversity Synthesis research group at iDiv and MLU.
“Many known factors are contributing to the population declines of many bird species, but our research adds a new dimension to our understanding of the potential causes of some of these changes: 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, may be something we humans should pay attention to, as we will most likely find ourselves living in places outside of our optimal climate ranges in the near future.”
