Birds nest earlier as climate heats up

Many birds are now nesting and breeding five to 12 days earlier than they did a century ago, in response to climate change, according to research from California. The findings add to the growing body of observed changes in bird behaviour, including shifts in migratory schedules and habitat ranges, that illustrate the profound ecological impact of temperature increases which to humans might seem relatively insignificant.  

“By nesting a week or 10 days earlier, birds are avoiding some of the negative effects of climate warming,” says study co-author Steven Beissinger, of the University of California Berkeley (UCB). It is good news, he says, to the extent “there may be more flexibility for species to respond to climate change than we thought”. 

The bad news, though, is “we don’t know yet whether staying in place and shifting schedules earlier is a permanent solution, or only provides temporary relief from the 2ºC rise in temperatures forecast to occur”.

Through nesting earlier, birds are taking advantage of cooler weather to compensate for the 1ºC rise in average temperature over the past century. Avian biology is particularly sensitive to temperature during nesting, the study by researchers from UCB and the University of Connecticut notes: baby birds have limited ability to regulate their own body temperatures; and the effort to feed their young means parent birds cannot afford to waste energy, such as flying in hotter weather.  

The research, led by Jacob Socolar and published in Proceedings of the National Academy of Sciences, is based on comparing new data with that first collected by pioneering UCB zoologist Joseph Grinnell between 1911 and 1929. Grinnell conducted extensive studies of California’s fauna, including birds, introducing a precise methodology to record field observations now known as the Grinnell System. 

Using his data as a baseline, UCB’s Grinnell Resurvey Project has been revisiting the same sites to assess how animals have responded to environmental changes. Previous analysis by several of the co-authors of this new paper has suggested about half of California’s birds have moved north or to higher elevations to escape hotter temperatures over the past 100 years.

Understanding the relationship between temperature and nesting was buttressed by data from 47,023 monitored bird nests across North America, collected as part of Project Nestwatch, a citizen science program run by the Cornell Laboratory of Ornithology in New York.

Frank La Sorte, a research associate with the Cornell lab, says birds provide a valuable resource for studying the implications of climate change for natural systems. “Information can be readily acquired on how the location and timing of life-history events are defined across the annual cycle, and how these spatial and temporal patterns are being affected by changing environmental conditions,” he says. “The findings from this study helps us to better understand how these factors may interact as birds respond to warming conditions.”

La Sorte and colleagues also drew on citizen science for research, published in July 2017, reporting the threat to bird species that breed in North America and winter in Central America. The near-term dangers of habitat loss, they concluded, was likely to be magnified by the long-term effects of climate change. 

“Evidence that birds are able to make adjustments in both space and time during the breeding season suggest that similar dynamics may be occurring during other phases of the annual cycle, La Sorte says. ”This flexibility may prove highly beneficial for the survival of bird populations, especially if this extends to long-distance migrants, whose complex life cycles are considered to be at particular risk of disruption under climate change.”

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