In contrast, when food is scarce, parents can be predicted to ignore begging and preferentially feed bigger chicks 8. When food is relatively plentiful, parents can be selected to preferentially feed the offspring signalling the greatest need 8. While each model is consistent with observations in some species, it is inconsistent with others 3.Ī possible explanation for this diversity is that different ecological conditions, in different species, favour different signalling systems 8, 22, 23, 24, 25. However, neither signal of need nor quality models predict that parents should flexibly ignore begging, as the hoopoe does 12, 17, 19. The pattern in those species may be better explained by ‘signal of quality’ models 3, 20, 21. This is clearly not the case in species where parents let the neediest offspring starve and offspring in better condition beg more 3, 13, 18, 19, 20, 21. However, these signal of need models assume that parents are trying to rear all their offspring and that offspring in better condition reduce their begging 3, 4, 9, 14, 17. The dominant paradigm, ‘signal of need’, predicts that chicks in worse condition beg with greater intensity and that parents respond to this begging 3, 14, 15, 17. All rights reserved, used with permission.Įvolutionary theory has been unable to account for this diversity across species, as highlighted by Mock et al. All rights reserved, used with permission and ( d) This figure is not covered by the CC BY licence ( c) G. ( c) This figure is not covered by the CC BY licence © L.M.R. All rights reserved, used with permission. ( b) This figure is not covered by the CC BY licence ©Damschen/ARCO/. Gouldian finch Erythrura gouldiae parents ( d) may preferentially feed offspring with elaborate structural ornaments around their mouths. 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. Tree swallows Tachycineta bicolor feed the chick begging the most ( a). However, the way parents respond to information about their offspring differs markedly across species. 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. In many siblicidal species, such as the blue-footed booby, the largest offspring beg and are fed the most 13. In other species, such as the hoopoe, mothers sometimes force food into the beaks of larger, silent chicks, ignoring the persistent begging from their smaller offspring 12. In many species, such as the tree swallow, smaller nestlings beg more, and are preferentially fed by their mothers 10, 11. Offspring attempt to influence the feeding behaviour of their parents by begging for food through a variety of mechanisms, including vocal calls, behavioural displays and physical structures 2.ĭifferent species, however, appear to beg and respond to begging in different ways ( Fig. Success or failure often depends on parents’ ability to determine which offspring to invest in, when to invest in them and how much to invest. Raising a brood successfully puts a metabolic demand on breeding birds that is the equivalent to a human cycling the Tour de France 1. In many species, including our own, the production of offspring represents the most energetically demanding stage of an animal’s life. Overall, these results show how ecological variation can lead to different signalling systems being evolutionarily stable in different species. In unpredictable and poor environments, parents pay less attention to begging, and instead rely on size cues or structural signals of quality. In predictable and good environments, chicks in worse condition beg more, and parents preferentially feed those chicks. We analyse parent–offspring communication across 143 bird species, and show that this variation correlates with ecological differences. This extreme variation across species, which contradicts predictions from theory, represents a major outstanding problem for the study of animal signalling. Furthermore, parents in some species even neglect smaller chicks that beg more, and preferentially feed the biggest chicks that beg less. Surprisingly, however, in a quarter of species studied, parents ignore begging chicks. A nest of begging chicks invites an intuitive explanation: needy chicks want to be fed and parents want to feed them.
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