Birds such as the cowbird that lay their eggs in the nests of other birds have evolved strategies to disguise their chicks and not just their eggs.
María De Mársico and her colleagues at the University of Buenos Aires observed eggs or hatchlings from the screaming cowbird (Molothrus rufoaxillaris; pictured left) or the shiny cowbird (Molothrus bonariensis) that were placed or laid in the nests of the baywing (Agelaioides badius; right), and measured the fledglings' survival rates. The researchers found that the baywing hosts rejected 83% of the shiny cowbird fledglings, but none of the screaming cowbirds. Analysis of the birds' plumage revealed that the differences in colour between screaming cowbird and baywing fledglings are likely to be indistinguishable to the avian eye. The begging calls of these species are also very similar, whereas the shiny cowbirds differ in their calls and appearance.
Proc. R. Soc. B http://dx.doi.org/10.1098/rspb.2012.0612 (2012)