Coprophagy by breeding birds, whereby parents eat the feces of their nestlings, is a common but rarely studied behavior. By eating feces, breeding parents may recycle nutrients. In many passerines, eating feces also reduces breeders' time away from the nest, saving energy and increasing brooding time. Here, we report the proportion of individuals that display coprophagy in a population of Dunnocks, Prunella modularis, in Dunedin (New Zealand), and evaluate whether coprophagy varies between sexes, and between two mating systems (monogamy and polyandry). We find that females consume fecal sacs significantly more frequently than males. We also find a non-significant trend for monogamous females to eat feces more often than polyandrous females. We conclude that two hypotheses – parental-nutritional and economical-disposal – could explain the differences in coprophagy between sexes. Our results also suggest that male Dunnocks may engage in coprophagy to recycle nutrients rather than for saving energy. Finally, we describe a novel observation of a nestling being fed with its own feces by an adult male.

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