Birds move closer to humans to avoid brood parasites

An international research team has recently discovered that Daurian redstarts, a passerine bird species, have evolved a strategy to avoid cuckoo brood parasitism. Cuckoo birds and other brood parasites lay their eggs in the nests of other species to be incubated and raised.

Cuckoo birds are weary of people and usually nest far from human-dominated environments. The researchers found that Daurian redstarts in northeastern China purposefully choose nesting sights near or even inside human settlements. As a result, their risk of becoming a host is reduced. 

The Daurian redstart has two breeding periods per season. During the first breeding event, cuckoos are not present. However, the cuckoos migrate to the area during the second breeding event.

The researchers noticed that the Daurian redstarts nested farther away from human settlements during the first breeding period, and then moved closer to human settlements in the second period when cuckoos were present. The experts concluded that the birds moved their nests closer during the second breeding period to avoid parasitism.

Moreover, the researchers were able to elicit this anti-parasitism strategy by presenting cuckoo models and artificial calls. Although these simulations were conducted during the first egg-laying period, the Daurian redstarts were motivated to move closer to human environments in response to the simulations. This suggests that the Daurian redstarts change their nesting behavior in response to the presence of cuckoos, regardless of the breeding period.

“We were able to show experimentally for the first time that Daurian redstarts adapt their nesting behavior depending on whether they notice cuckoos in the area,” said Jinggang Zhang, a researcher at the Max Planck Institute for Biological Intelligence. 

We must wonder about the ecological impacts of this interaction in an ever-changing environment. 

“Urbanization affects habitats and animal populations around the world in many ways. Cuckoos may have to adapt to this development by venturing closer to human settlements as well, or by expanding the range of host species,” said Bart Kempenaers, a director at the institute. 

A second study conducted by the researchers demonstrates the cuckoo’s adaptability. Daurian redstarts have two colored eggs – red and blue. The research team found that female cuckoos showed a “clear preference for nests with blue eggs”  in the hopes that the foster parents will not reject the parasitic egg.

“We were surprised to find such a clear preference for nests with blue eggs,” said Kempenaers. “Our observations suggest that cuckoo females are quite sensitive to characteristics of the nest and do not just dump their eggs in any host nest they can find.” 

The research is published in the journal Current Biology.

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By Erin Moody, Earth.com Staff Writer

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