Behavior of the Avian Parasite Philornis downsi (Diptera: Muscidae) in and Near Host Nests in the Galapagos Islands

Abstract

The Avian Vampire Fly, Philornis downsi, has invaded the Galapagos Islands, where it causes high mortality of endemic and native landbird species, including most species of Darwin’s finches. Control methods are under development, but key information is missing about the reproductive biology of P. downsi and the behavior of flies in and near nests of their hosts. We used external and internal nest cameras to record the behavior of P. downsi adults within and outside nests of the Galapagos Flycatcher, Myiarchus magnirostris, throughout all stages of the nesting cycle. These recordings showed that P. downsi visited flycatcher nests throughout the day with higher fly activity during the nestling phase during vespertine hours. The observations also revealed that multiple P. downsi individuals can visit nests concurrently, and that there are some interactions among these flies within the nest. Fly visitation to nests occurred significantly more often while parent birds were away from the nest than in the nest, and this timing appears to be a strategy to avoid predation by parent birds. We report fly mating behavior outside the nest but not in the nest cavity. We discuss the relevance of these findings for the adaptive forces shaping P. downsi life history strategies as well as rearing and control measures.

Life-stage and sex influencePhilornisectoparasitism in a Neotropical woodpecker (Melanerpes striatus) with essential male parental care

“…Unfortunately, almost nothing is known about the temporal activity patterns of Philornis on Hispaniola nor for most other Philornis with subcutaneous larvae. In the Galápagos, adult P. downsi enter host nests to oviposit when the parent birds are absent during the day when nestlings are young and at night when nestlings are older (O'Connor et al 2010), and peak nest visitation rates of adult flies occurs in the late afternoon and dusk in the nestling phase (Pike et al 2021). But P. downsi larvae are free-living and hematophagous and eggs are oviposited in the nest.…”

“…), a form of essential parental care. This male-biased nocturnal incubation and brooding behavior might be important because adults of at least some Philornis species will visit nests at night (O'Connor et al 2010) and in the late afternoon and dusk (Pike et al 2021). If overnight incubation and brooding increase exposure (H3b), Philornis (P3.1b) prevalence and (P3.2b) intensity should be higher for nesting males than nesting females.…”

Persistence of the invasive bird-parasitic fly Philornis downsi over the host interbreeding period in the Galapagos Islands

“…Our study period included 2015, which has been classified as an El Niño year 35 , 36 , and was thus characterized by higher rainfall than usual. Given the precipitation patterns at our field site and several cases of finches breeding in June and July 48 , we conclude that the nesting season was increased by 4–6 weeks during 2015.…”

“…There are limited records of cool-season nesting for two of these species. The Galapagos Flycatcher, Myiarchus magnirostrus , nests in cavities and is known to breed during the hot season 48 , 51 . However, an active flycatcher nest was discovered with nestlings and P. downsi at the CDRS during August 2014 52 as well as in June of 2015 at our field site 48 .…”

“…The Galapagos Flycatcher, Myiarchus magnirostrus , nests in cavities and is known to breed during the hot season 48 , 51 . However, an active flycatcher nest was discovered with nestlings and P. downsi at the CDRS during August 2014 52 as well as in June of 2015 at our field site 48 . Another possibility is the Galapagos Dove, Zenaida galapagoensis .…”