Birds that maintain their historical breeding times because their internal clocks are set to changes in day length may have fewer chicks survive because the food source they rely on already came and went
A study of the University of Michigan (UM) suggested that human-caused noise and light pollution can harm individual species of bird populations.
The researchers looked at a huge collection of data sets to assess how artificial light and human-caused noise affected the reproductive success of 58,506 nests from 142 bird species across North America. They considered several factors for each nest, including the time of year breeding occurred and whether at least one chick fledged from the nest.
The researchers found that light pollution causes birds to begin nesting as much as a month earlier than normal in open environments, such as grasslands or wetlands, and 18 days earlier in forested environments.
The consequence could be a mismatch in timing - hungry chicks may hatch before their food is readily available.
As the planet warms, birds' food is available earlier due to warmer weather. Birds that maintain their historical breeding times because their internal clocks are set to changes in day length may have fewer chicks survive because the food source they rely on already came and went.
These findings suggest two conclusions about birds' responses to climate change. First, at least temporarily, birds in artificially lit conditions may be tracking climate change better than those in dark areas. Second, when scientists thought birds were adjusting their reproductive timing to climate change, birds may have actually been responding to light cues instead, because many studies were done in areas exposed to some light pollution.
The researchers then delved into greater detail for 27 bird species. They found that a bird's ability to see in low light and the pitch of its call were related to the species' responses to light and noise pollution, respectively.
The more light a bird's eye is capable of taking in, the more that species moved its breeding time earlier in the year in response to light pollution and the more that species benefited from light pollution with improved nest success.
Having examined the effects of noise pollution, the researchers found that birds living in forested environments tended to be more sensitive to noise than birds in open environments.
Noise pollution delayed nesting for birds whose songs are at a lower frequency and thus more difficult to hear through low-frequency, human-caused 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 breed.
These trait- and environment-specific results have strong implications for managing wildlands, according to the researchers.
The study is the first step toward a larger goal of developing a sensitivity index for all North American birds. The index would allow managers and conservationists to cross-reference multiple physical traits for one species to assess how factors such as light and noise pollution would affect each species.
The study is published Wednesday online in the journal Nature.