Figure 1. Variation in parental provisioning.

In every species of bird with parental care, chicks appear to have evolved signals designed to maximize their chance of being fed, such as vocalizations, begging postures and bright mouths. However, the way parents respond to information about their offspring differs markedly across species. Tree swallows Tachycineta bicolor feed the chick begging the most (a). Others sometimes neglect begging offspring, such as the blue-footed booby Sula nebouxii (b) and the hoopoe Upupa epops (c) which instead preferentially feed larger chicks. Gouldian finch Erythrura gouldiae parents (d) may preferentially feed offspring with elaborate structural ornaments around their mouths. (Photos courtesy of (a) M. Sodicoff. (b) This figure is not covered by the CC BY licence ©Damschen/ARCO/naturepl.com. All rights reserved, used with permission. (c) This figure is not covered by the CC BY licence © L.M.R. Gordón. All rights reserved, used with permission; and (d) This figure is not covered by the CC BY licence (c) G. Grall, National Aquarium, Baltimore. All rights reserved, used with permission.