Cuckoos mimic hawks to scare hosts

Cuckoos have a bad reputation, and it's probably going to get worse. They're known for being brood parasites, depositing their eggs in the nests of other bird species. When these hatch, the cuckoo chicks aggressively demand food from the host parents and also eject their unfortunate step-siblings from the nest. As a result, the cuckoo gets a free pass on child-raising.

It is little surprise that cuckoos coming in to lay their parasitic eggs are often 'mobbed' by the birds that they target, in order to drive them away. However, a recent study has found that 'naive' birds are reluctant to approach cuckoos that have a barred (striped) pattern on their undersides, compared to cuckoos that lack such a pattern. This is interpreted as a form of Batesian mimicry by the cuckoos, taking on the stripes of sparrowhawks, which are birds of prey.

Cuckoos therefore may use two different kinds of mimicry in their lives: as adults mimicking birds of prey to prevent host birds from attacking them, and in the nest mimicking host chicks to convince the host parents to feed them.

Sources:

• "Cuckoos mimic hawks to scare their hosts, says research," by Victoria Gill. BBC Earth News, 17 April 2011
• Welbergen, J. A. & N. B. Davies, 2011. A parasite in wolf's clothing: hawk mimicry reduces mobbing of cuckoos by hosts. Behavioral Ecology. First published online 21 Mar 2011, doi: 10.1093/beheco/arr008 [abstract].