Urban noise affects the color of songbirds’ beaks

Recently, there have been growing concerns in the scientific community that anthropogenic noise has a number of damaging effects on wildlife in urban environments. Anthropogenic noise contains a wide range of frequencies, types of sounds (such as those from traffic), and varying amplitudes, including sounds with rapid onset times which can be startling.

Although previous studies have argued that noise pollution can affect cognitive performance in many animal species, including songbirds, a new study led by Florida Atlantic University is the first to test whether exposure to urban noise affects also the coloration of these birds’ beaks.

The scientists focused on zebra finches (Taeniopygia guttata), a species of songbirds in which males have a colorful plumage of white, black, gray, brown, and orange, while females are all gray. In addition, males have bright red beaks and females have orange beaks. This beak ornamentation is a social signal and a secondary sexual trait which can signal a male’s quality and affect females’ mate preference, while also affecting dominance hierarchies in male zebra finches.

The researchers conducted two separate experiments to investigate the effects of anthropogenic noise on cognition, growth, and beak coloration in these songbirds. In the first experiment, they tested adult zebra finches on a variety of cognition assays during exposure to playbacks of urban noise versus exposure to other types of natural sounds. In the second experiment, the experts measured the cognitive performance on adult zebra finches after raising them with consistent exposure to urban noise. 

Afterward, the team compared the birds’ performance to that of birds exposed to “pink noise” (a type of noise control) or to normal sounds of the aviary. Moreover, the researchers tracked their growth and development of beak coloration during the first 90 days of the birds’ lives.

The analysis revealed that exposure to urban noise caused the birds to take longer to learn novel foraging tasks and association-learning tasks. Although exposure to such sounds did not seem to affect growth rate or adult body size, males tended to develop less bright beak coloration, while females developed beaks with brighter, orange coloration.

“Our finding suggest that urban noise exposure may affect morphological traits, such as beak color, which influence social interactions and mate choice,” said study senior author Rindy C. Anderson, an associate professor of Biology at FAU. “However, the mechanisms by which noise affects beak ornamentation remain unclear. If traffic noise raises corticosterone levels and corticosterone levels affect beak color, then it is possible that stress is mediating the effects of noise exposure on beak ornamentation.”

“Further research should investigate the effects of beak ornamentation on social hierarchies and mate selection in urban environments, and test whether social interaction in noisy environments can ameliorate negative effects from urban noise on traits such as problem-solving and neophobia or fear of new things,” she concluded.

The study is published in the journal Acta ethologica.

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By Andrei Ionescu, Earth.com Staff Writer

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