Quality of environment explains why some birds choose to neglect their hungriest chicks

March 30, 2016

Scientists have long been aware that in some species of bird, parents will prioritise feeding the neediest chicks, whereas in others they will focus on the strongest offspring. Until now, though, the reason behind this discrepancy has remained a mystery.

A comprehensive new study from the University of Oxford finds that the quality of the local environment can explain which chicks in a nest a parent bird decides to feed. This helps resolve a long-standing question in ecology about whether parents respond to signals of need (such as how much a chick begs) or signals of quality (such as a chick's colour) when making feeding decisions.

For example, species living in favourable, predictable environments (such as tree swallows in North America) choose to feed begging chicks that are in poorer condition relative to their siblings, whereas parent birds in unfavourable, unpredictable environments (such as blue-footed boobies in the Galápagos Islands) preferentially feed chicks that are in the best condition, regardless of how much other siblings in the nest beg.

The study is published in the journal Nature Communications.

Shana Caro, a PhD student in Oxford's Department of Zoology who led the research, said: 'There have been hundreds of studies looking at the phenomenon of begging in birds, many of which have found strange results and contradictory patterns.

'Our analysis of these studies found that there is a universal explanation for these discrepancies: the predictability and quality of the local environment.'

The researchers compiled the available literature – more than 300 studies – on the parental care preferences during feeding of 143 bird species across the globe and analysed how this variation in care relates to the condition and behaviour of offspring, as well as the environmental conditions in the area in which each species is found.

Shana Caro said: 'In good ecological conditions, such as those with predictable and abundant sources of food, you tend to find that the chicks in greatest need of food make the most noise and do the most begging.

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