Biologists have suspected for some time that certain animals identify prime breeding real estate by monitoring the reproductive success of neighborhood conspecifics. To test this so-called public information hypothesis, Blandine Doligez of the University of Bern in Switzerland and her colleagues transferred baby collared flycatchers between nests among breeding plots on the Swedish island of Gotland, creating some plots with big broods and others with only a few nestlings. Subsequent observations of immigration and emigration rates revealed that prospective residents spy on the locals and preferentially move to plots abounding with chicks. For their part, parents of the newly enlarged broods found that they had too many mouths to feed and their wards grew scrawny. Consequently, they moved out.
"These results," Doligez and her collaborators conclude, "could only be explained by the use of public information" by the flycatchers. Exactly how widespread this breeding habitat selection strategy is remains in question. But the authors note that another recent study of colonial seabirds yielded similar results.