Brood parasites are organisms that rely on others to raise their young. Among the birds it is commonly found in the cuckoos, though there are nonparasitic cuckoo species too.The brood parasite manipulates a host, either of the same or of another species, to raise its young as if it were its own. Brood parasitism relieves the parasitic parent from the investment of rearing young or building nests for the young, enabling them to spend more time on other activities such as foraging and producing offspring. The risk of egg loss is mitigated, as eggs are distributed amongst a number of different hosts. As this behaviour is damaging to the host, it often results in an evolutionary arms race between parasite and host. In the picture is a common cuckoo chick being raised by a reed warbler.
Photo: Per Harald Olsen