Brood Parasitism Risk Drives Birds to Breed Near Humans

Although humans have generally negative effects on wildlife, some animals live in close proximity to human residences. Why some animals choose to settle near humans remains a long-standing puzzle. Settling near humans or in urban environments may be beneficial, because of the availability of resources such as food (e.g. supplemental feeding) [1] or suitable nest sites (e.g. cavities) [2, 3], or because of reduced predation risk if predators avoid settlements [4, 5]. Here, we report on a study of Daurian redstarts <i>Phoenicurus auroreus</i>, a common host of the common cuckoo <i>Cuculus canorus</i>, to show that settling near humans can also be a strategy employed by hosts to avoid brood parasitism. First, redstarts suffered an increased risk of brood parasitism with increasing distance from the nearest building. Second, redstarts adjusted their nesting location in response to a seasonally predictable change in the risk of brood parasitism. Third, experimentally simulating the presence of cuckoos during a period when they are naturally absent increased the likelihood that redstarts nested indoors or closer to human settlements. These findings suggest that redstarts actively choose to place their nest in the vicinity of a human residence as a defense against cuckoos. Hence, settling near humans may be an anti-parasitism strategy in some avian hosts.