Noise and light alter bird nesting habits and success

Are you looking for a bird’s-eye view of human impact? A new study published in the journal Nature provides the most comprehensive picture of how human noise and light pollution affect birds across North America, including how these factors can interact or mask the impacts of climate change.

Recent troubling results suggest that bird populations have declined by more than 30% over the past few decades. To develop effective strategies to reverse this trend, scientists and land managers need to understand what caused 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 Clint Francis, a biologist at California Polytechnic State University and a of the main authors of the study.

The researchers looked at a large collection of data sets, including those collected by citizen scientists through the NestWatch program, to assess how light and noise affected the reproductive success of 58,506 nests of 142 species across North America. The team considered several factors for each nest, including the time of year when breeding occurred and whether at least one chick escaped the nest.

Birds schedule their breeding to coincide with peak food availability to feed their young, using daylight signals to breed around the same time each year. 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 in timing – hungry chicks 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’ with the transition to early food availability due to climate change.”

These findings suggest two conclusions about how birds respond to climate change. First, at least temporarily, birds in areas affected by light pollution can follow climate change better than those in darker natural habitats. Second, when scientists thought birds were adapting their breeding times to climate change, the birds may actually have responded to light signals instead because many studies have been conducted in areas exposed to some light pollution.

When considering noise pollution, the results showed that birds living in wooded environments tend to be more sensitive to noise than birds in open environments.

Researchers delved into details for 27 species looking for physical traits that could explain the variations in species responses to light and noise. A bird’s ability to see in low light conditions and the tone of its call correlated with species responses to light and noise pollution, respectively.

The more light a bird’s eye can absorb, the more the species shifted its breeding period to the beginning of the year in response to light pollution, and the more the species experienced better nest success due to ‘light pollution. Noise pollution has delayed the nesting of birds whose songs are at a lower frequency and therefore more difficult to hear through low-frequency human 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 specific environmental traits and findings have strong implications for wilderness management.

“We have convincingly shown in many species that noise and light pollution are having strong effects on wild populations,” Francis said. “If there is a proposed development and land managers are concerned about a bird they have no information about, they can use this study to see if the development is likely to affect the bird. Is it a forest bird? If so, it is likely to be more sensitive to light and noise. “

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-reference multiple physical traits of a species to assess how factors such as light and noise pollution would affect it and each species.

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Link to the original study in Nature, “Sensory Pollutants Alter the Phenology and Physical Form of Birds on a Continent”: https: //www.nature.with/articles /s41586-020-2903-7