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The white-breasted nuthatch has good low-light vision and has anticipated nesting times in response to light exposure, according to a new study in the journal Nature. Image credit: Dave Keeling
Are you looking for a bird’s-eye view of human impact? A new study in the journal Nature provides the most complete picture of how human-caused noise and light pollution affects birds in North America, including how these factors can interact or mask the impacts of climate change.
Recent troubling findings suggest that North American bird populations have declined dramatically over the past few decades. To develop effective strategies to reverse this trend, scientists and land managers need to understand what is causing the decline.
The effects of noise and light pollution on the health of bird populations had been largely overlooked until recent studies suggested that these stressors can harm individual species. With this new study, a continent-wide picture has emerged.
“Our study provides the most comprehensive evidence that noise and light can profoundly alter bird reproduction, even when other aspects of human activity are taken into account,” said biologist Clint Francis of California Polytechnic State University, one of the lead authors of the study.
“This work underscores the enormous extent of human-made noise and light and their pervasive influence on the important animals we share landscapes with,” said study co-author Neil Carter, conservation ecologist at the School for Environment and Sustainability of the University of Michigan. Former UM postdoctoral researcher Mark Ditmer is also a co-author.
The paper, “Sensory Pollutants Alter the Phenology and Physical Form of Birds on a Continent,” was published online on November 11.
The research team looked at a huge collection of data sets, including those collected by citizen scientists through the NestWatch program, to assess how artificial light and human-caused noise affected the reproductive success of 58,506 nests of 142 species. of birds throughout North America. They considered several factors for each nest, including the time of year when breeding occurred and whether at least one chick escaped the nest.
The western bluebird has benefited from light pollution in terms of reproductive success, according to a new study in Nature. Image credit: Dave Keeling
Birds schedule their breeding to coincide with peak food availability to feed their young, using daylight signals to breed at the same time each year. The researchers found that light pollution causes birds to start nesting up to a month earlier than normal in open environments, such as grasslands or wetlands, and 18 days earlier in wooded environments.
The consequence could be a mismatch between time-hungry chicks that may hatch before their food is readily available. If that happens, these early season nests may be less successful in fledging at least one chick, but the situation is complicated by climate change.
As the planet warms, bird food is available sooner due to the warmer climate. Birds that keep their breeding times historical because their internal clocks are set to changes in the length of the day can survive fewer chicks because the food source they rely on already came and went.
“We found that birds that anticipated their breeding times in response to increased light pollution actually have better reproductive success,” said Francis. “A likely interpretation of this response is that light pollution actually allows these birds to ‘catch up’ in the transition to earlier food availability due to climate change.”
These findings suggest two conclusions about birds’ responses to climate change. First, at least temporarily, birds in artificial lighting conditions could track climate change better than those in dark areas.
The northern cardinal has a relatively low-frequency song and has delayed playback in response to noise pollution, according to a new study in the journal Nature. Image credit: Dave Keeling
Second, when scientists thought birds were adapting their breeding times to climate change, the birds may have actually responded to light signals, because many studies have been conducted in areas exposed to some light pollution.
Researchers delved into details for 27 bird species, looking for physical traits that could explain the variations in the species’ responses to light and noise. Common sources of light pollution include the glare of city lights, and common sources of human-caused noise include highway traffic and planes flying overhead.
They found that a bird’s ability to see in low light conditions and the tone of its call correlated with the species’ responses to light and noise pollution, respectively.
The more light a bird’s eye can absorb, the more the species has shifted its breeding time to the beginning of the year in response to light pollution and the more it benefited from light pollution with better nest success .
When looking at the effects of noise pollution, the researchers found that birds living in wooded environments tended to be more sensitive to noise than birds in open environments.
Noise pollution has delayed the nesting of birds whose songs are at a lower frequency and therefore more difficult to hear through human-caused low-frequency noise. Mating decisions are made based on the male’s song and, in some cases, females need to hear the male’s song to become physically ready to reproduce.
These trait-specific and environment-specific findings have strong implications for wilderness management, according to the researchers.
“This work directly informs the conservation of wild bird populations,” UM’s Carter said. “Land managers and conservation operators, for example, can prioritize the habitats and species most at risk from light and noise pollution and better assess the environmental impacts of new developments, as well as mitigate existing ones.
“We also hope that our results will motivate people and communities to reduce their light and sound footprints.”
The study is the first step towards a broader goal of developing a sensitivity index for all North American birds. The index would allow managers and conservationists to cross multiple physical traits of a species to assess how factors such as light and noise pollution would affect each species.
In addition to Francis, Carter and Ditmer, the authors of the Nature article are Masayuki Senzaki, Jennifer Phillips and Ashley Wilson of Cal Poly; Jesse Barber and Christopher McClure of Boise State University; Caren Cooper and Jelena Vukomanovic of North Carolina State University; Kurt Fristrup of the National Park Service; Daniel Mennitt of Exponent engineering and scientific consulting; and Luke Tyrrell of the State University of New York at Plattsburgh.
The work was supported by grants from the National Science Foundation, NASA, and the Japan Society for the Promotion of Science.
Once the document has been published online, it will be available on nature.com.
Press release written by Rachel Henry of California Polytechnic State University, with additional material provided by Jim Erickson of the University of Michigan.
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