Parental care in Darwin's finches

Selection should act on parental care and favour parental investment decisions that optimise the number of offspring produced. Such predictions have been robustly tested in predation risk contexts, but little is known about parental care investment trade-offs under conditions of parasitism. The avian vampire fly, Philornis downsi (Diptera: Muscidae), is a myasis-causing ectoparasite accidentally introduced to the Galápagos Islands, and one of the major causes of failure in Darwin’s finch nests. With an 11-year dataset spanning 21 years, we examine the relationship between parental care behaviours and the number of fly larvae and pupae in Darwin’s finch nests. We do so across three host species (Camarhynchus parvulus, C. pauper, Geospiza fuliginosa) and one hybrid Camarhynchus group. Nests with longer female brooding duration had fewer parasites, and this effect intensified with higher male food delivery to chicks. Neither male age nor number of nest provisioning visits alone were direct...