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

Abstract

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).

Assessing dietary specialization to inform the conservation of the fairy pitta (Pitta nympha), an endangered vermivore

“…, Fig. 1A ), this may suggest that when foraging pittas are unable to find enough earthworms, they resort to non-earthworm prey items of smaller size, resulting in higher number of items in a beak-load because non-earthworm types are not sundered ( Park et al, 2022 ) and take less space in the beak. Alternatively, if birds aim to deliver a load of similar nutritional value on average, it implies one earthworm is replaced with several smaller, less nutritious prey items.…”

“…Field work was previously described in Park et al (2022) . From May to July 2012, 2013, and 2017, we (JP) observed nestling provisioning at four fairy pitta nests in Namhae-gun in southern Republic of Korea (127°54′E, 34°50′N; no.…”

“…From videos and photos, we extracted the following variables for statistical analyses. Several variables listed below were also used in our earlier research ( Park et al, 2022 ). Subsequent analyses using the extracted variables were performed on a subset of visits, excluding the first visit each day.…”

“…These data were excluded from statistical analyses regarding prey length. Parents often sundered prey, primarily earthworms, into pieces ( Park et al, 2022 ). To determine the length of the prey before sundering, we identified its color, thickness (diameter), and segment patterns (size and location) at the sundered point for each piece.…”

Conservation of avian diet specialists: lessons from brood provisioning ecology of the endangered vermivore, the Fairy Pitta (Pitta nympha)

“…For example, the Indian Pitta, Pitta brachyura prefers to breed in evergreen broad-leaved forests along ravines where surface living earthworms are abundant 23 , and the number of nests of the Rainbow Pitta, Pitta iris was positively correlated with both rainfall and earthworm abundance 34 . As earthworms are the most important food source, especially for the young nestlings, it is not surprising that the Fairy Pitta appears to have developed a special behavioral adaptation for handling and carrying earthworms to the nest: earthworm sundering 35 , which also occurs in other avian vermivores 2,4,6,7,35,36 .…”