Information is power, even for birds. Researchers report that collared flycatchers decide where to nest and whether to return the next year based in part on knowledge of their neighbors' reproductive success.
Choosing a good breeding site may mean the difference between begetting many offspring or none at all. So a team led by Blandine Doligez, now at the University of Bern, Switzerland, wanted to know whether birds make use of information gleaned by watching their neighbors. Doligez investigated the question at a long-term research site at Gotland, Sweden, where researchers had noticed flycatchers peering into the nest boxes of other birds. "I thought, 'that's really a sign,' " Doligez recalls.
Some subterfuge was required in order to check whether the birds used their spying in decisions. The researchers took nestlings from some nests and added them to others, creating plots of woodland with either supersized or measly broods. The team then monitored these plots and two types of control areas for 3 years. The manipulation had a marked effect. Birds from outside the area preferentially moved to plots with many nestlings, apparently judging these plots to be productive.
But the extra mouths meant that parents had to spread food more thinly, so youngsters on these plots were smaller. Resident birds apparently picked up on those cues--and nested elsewhere the next year. Residents weren't happy with meager nests, either: They fled those plots at equally high rates, the team reports in the 16 August issue of Science. Emigrating birds "know what's going on in their own area," Doligez concludes. Immigrants, however, are at a disadvantage and may be unable to pick up on relatively subtle clues, she says.
Such findings highlight the importance of animal behavior to population biology, notes conservation biologist J. Michael Reed of Tufts University in Medford, Massachusetts. "Dispersal is often treated as diffusion in population models even though for many species it is a result of a series of behavioral decisions," Reed says. The work may also prove useful for conservation efforts to reintroduce species to new areas, he adds.