Sundering of earthworms by the Fairy Pitta (Pitta nympha): an unexplored strategy of prey preparation for brood provisioning by avian vermivores

Ecological specialists utilize a restricted range of resources and have evolved adaptations to exploit their specialized resources. For example, avian insectivores that feed nestlings with grasshoppers, beetles, or moths perform insect prey preparation before feeding nestlings so that the nestlings are able to swallow the prey. This behavior is generally not expected for soft prey such as earthworms. However, an overview of photographic evidence available online suggested that earthworms are sundered by parents before bringing the prey to the nestlings in a range of species from several families of vermivores worldwide. Reports on the provisioning of nestlings by the vermivores are relatively scant and no report on earthworm sundering has been published. We studied earthworm sundering performed by parents provisioning their broods at four nests of the Fairy Pitta in Korea. The birds sundered earthworms more often when nestlings were smaller and when the earthworm was longer. This is the first quantitative description of earthworm sundering in avian vermivores. We present and evaluate four hypotheses for the function of sundering: provisioning of small nestlings, decreased detectability, hunting multiple prey, and transport of prey. Among these, provisioning of small nestlings seems the most feasible explanation of sundering by the Fairy Pitta as sundering the earthworm allows parents to efficiently provision the younger/smaller nestlings who would have difficulties swallowing unsundered earthworms. This specialized prey preparation technique of vermivores suggests a tight adaptive match between their parental behaviors and their diet (vermivory).