Brood parasitic nestlings benefit from unusual host defenses against botfly larvae (Philornis spp.)
Brood parasitic birds lay their eggs into the nests of other birds, abandoning parental care of their nestlings to the unsuspecting hosts. Parasite and host nestlings may themselves be parasitized by botfly larvae (Philornis: Muscidae), which burrow under the nestlings’ skin and can seriously affect growth and survival. Here, we provide the first direct evidence that adult baywings (Agelaioides badius), the primary host of the specialist brood parasitic screaming cowbird (Molothrus rufoaxillaris), regularly remove botfly larvae from their own and parasitic nestlings by pulling them out of the nestlings’ skin. This is the only bird species known to remove botfly larvae. By combining nestling cross-fostering with video recording of baywing nests, we show that due to prompt removal, infection with botfly larvae had negligible effects on nestling growth and survival despite high prevalence. Our results provide the first direct observations for larva removal behavior in botfly hosts. Screaming cowbirds may benefit from using baywings as its main host, as larva removal by adult baywings reduces the costs of botfly parasitism.
Infection by botfly larvae of the genus Philornis (Muscidae) causes nestling mortality in many Neotropical birds. Despite the lethal effects, most Philornis hosts studied so far lack specific defenses against these larvae. The grayish baywing (Agelaioides badius), primary host of the brood parasitic screaming cowbird (Molothrus rufoaxillaris), is the only species that, based on indirect evidence, would be able to remove Philornis larvae from infected nestlings. We provide the first direct evidence that adult baywings do indeed remove botfly larvae from their own nestlings as well as from parasitic cowbird nestlings and that this unusual defense may increase the survival of own and screaming cowbird nestlings at infected nests.
KeywordsPhilornis sp. Ectoparasitism Brood parasitism Allopreening Heterospecific cleaning Cowbird
We thank Fundación Elsa Shaw de Pearson for allowing us to conduct this study at Reserva El Destino and Vanina Fiorini, Florencia Lama and Juan Manuel Rojas Ripari for help with the fieldwork. We are grateful to Christina Riehl and two anonymous reviewers for providing valuable comments on the manuscript.
The datasets generated and analyzed during the current study are available from the corresponding author on reasonable request.
CAU is supported by a fellowship from the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). MCDM and JCR are Research Fellows of CONICET. This work was supported by grants to JCR of Agencia Nacional de Promoción Científica y Tecnológica (PICT 2011-0045) and University of Buenos Aires (Ubacyt W808).
Compliance with ethical standards
Conflict of interest
The authors declare they have no conflict of interest.
Research presented in the manuscript was conducted in accordance with the Argentine law. The study was conducted under permit (202/12) from the local authority (OPDS, Province of Buenos Aires, Argentina). All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. As the experimental protocols involving handling of birds were of minimal impact, the University of Buenos Aires committee for animal care and use did not intervene. No nestlings died or were injured during manipulations, and experimental infection had negligible effects on nestling growth and survival.
- Arendt WJ (1985) Philornis ectoparasitism of pearly- eyed thrashers. I. Impact on growth and development of nestlings Auk 102:270–280Google Scholar
- Davies NB (2000) Cuckoos, cowbirds and other cheats. Oxford University Press, OxfordGoogle Scholar
- Ortega C (1998) Cowbirds and other brood parasites. The University of Arizona Press, TucsonGoogle Scholar