Sometimes bird mommies and dads have to pick which of their chicks to feed. According to a new Nature Communications study, that decision is heavily dependent on environmental conditions. Parents in a quarter of the bird species examined ignore their beg chicks, and some even neglect smaller chicks that implore more in favor of bigger chicks that beg less.
Birds spend a lot of energy looking for food to sustain their brood, and researchers have long puzzled over how parents decide which of their progeny to invest in, when, and how much. Previous work revealed that creating a brood successfully is as metabolically demanding for breeding birds as cycling the Tour de France is for humans.
Most chicks have evolved behaviors and signals designed to maximize their chances of being fed: vocal calls, praying postures, and bright mouths with colorful decorates or ultraviolet reflectance, for example. How mothers respond differs a lot across species. Some bird mothers, like tree swallows, feed the chicks that implore the most. Others might dismiss persistent implore and feed the biggest( and silent) chicks instead, such as the hoopoe. And in siblicidal species, like blue-footed boobies on the Galapagos, bigger chicks implore and get more food, while smaller chicks are left to starve. Precisely how mothers prefer signals of quality over signals of want( or vice versa) is a mystery.
University of Oxfords Stuart West and colleagues conducted a literature search use Web of Science and Google Scholar on parental care preferences during feeding. They aimed up with 306 analyzes on 143 bird species from around the world. They then analyzed how difference in mothers options are related to factors ranging from chick condition to ecological conditions.
The team found that when the environment is predictable and good, chicks in poorer health pray more, and their parents feed them more. When food is plentiful, all the progeny might survive. But when the environment is unpredictable and less favorable yet an optimistic number of eggs were laid parents tend to feed chicks with the best health, regardless of how much the other nestlings beg. The mothers pay less attention to begging, relying instead on signals of quality, such as size.
The findings suggest that ecological variation can lead to different, yet evolutionarily stable, parent-offspring communication systems in different species. Some birds can even adjust their responses: When theres extra food, hihi parents become less sensitive to mouth color in their progeny, and alpine swifts who breed early in the season when theres more food favor nestlings with lower ultraviolet reflectance.
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