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

Courtney L Pike,Birgit Fessl,Ismael E Ramirez,Charlotte E Causton,George E Heimpel,David J Anchundia

doi:10.1007/s10905-021-09789-7

Courtney L Pike, Birgit Fessl + Show 4 more

Open Access

https://doi.org/10.1007/s10905-021-09789-7

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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.

Highlights

Island ecosystems are increasingly challenged by invasive species that have been introduced by humans (Simberloff 2010; Bellard et al 2017; Spatz et al 2017; Lenzner et al 2020)
Video recordings taken outside and within nests of the Galapagos Flycatcher that were heavily infested with P. downsi have provided new insights into the behavior of this invasive parasitic fly, though results should be interpreted with some caution given the low sample size and the limited data collection period for two nests
By tracking three nests during the nestling phase and monitoring fly activity from the onset of the incubation phase to post-fledging in one of these, we determined that P. downsi visitation of nests appears to be highly dependent on the time of the day and is influenced by the presence of adult birds; when birds are in the nest, flies rest outside the nest until the birds leave

Summary

Introduction

Island ecosystems are increasingly challenged by invasive species that have been introduced by humans (Simberloff 2010; Bellard et al 2017; Spatz et al 2017; Lenzner et al 2020). While the first report of P. downsi in bird nests occurred in 1997 (Fessl et al 2001), records in museums date back to the 1960 s (Causton et al 2006; Fessl et al 2018) This fly is native to mainland South America and Trinidad (Bulgarella et al 2015; Fessl et al 2018; Koop et al 2020), but it has a widespread distribution and broad host range in Galapagos, infesting nests of at least 21 small landbird species (Fessl, et al 2018; Anchundia and Fessl 2020; Coloma et al 2020). Control options that are being evaluated include insecticidal treatment of nests and trapping as stop-gap methods and biological control and the Sterile Insect Technique as long-term options (Knutie et al 2014; Heimpel 2017; Bulgarella et al 2017; Fessl et al 2018; Boulton et al 2019; Bulgarella et al 2020; Ramirez et al Accepted)

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