Is the grass always greener on the other side? Weak relationships between vegetation cover and parasitic fly infestations.

Understanding parasite-host ecology is increasingly important for conservation efforts in a changing world. Parasitic nest flies in the genus Philornis (Diptera: Muscidae) have been implicated in the decline of endemic island species and are also known to negatively impact breeding success of the critically endangered Ridgway's hawk (B. ridgwayi) on the island of Hispaniola. Despite the importance of these effects on hosts, and extensive research of Philornis downsi in the Galápagos, the ecology of most species of philornid nest flies is poorly understood. We examined biotic factors related to Philornis pici infestations of nestling Ridgway's hawks in the Dominican Republic, where both fly and hawk are native. We found grass-cover was negatively associated with P. pici infestations, while coverage and height of other vegetation classes (tree, shrub, herbaceous, and bare ground) had no association, which is interesting considering recent landscape-level changes to Ridgway's hawk habitat. Anthropogenic activities in Los Haitises National Park, the last strong-hold of Ridgway's hawk, have shifted the landscape from primary forest to a fragmented secondary forest with smallholder or subsistence farms and grassy patches. New information on the ecology of nest flies in their native habitat can inform conservation efforts and allow us to make recommendations for future research.

More than just nestlings: incidence of subcutaneous Philornis (Diptera: Muscidae) nest flies in adult birds.

Philornis flies Meinert (Diptera: Muscidae) have been documented parasitizing over 250 bird species, some of which are endemic species threatened with extinction. Philornis parasitism is hypothesized to affect nestlings disproportionately more than adult birds because limited mobility and exposed skin of nestlings increase their vulnerability to parasitism. We used a comprehensive literature review and our recent fieldwork in the Dominican Republic, Puerto Rico, and Grenada to challenge the idea that parasitism by subcutaneous Philornis species is a phenomenon primarily found in nestlings, a fact that has not been quantified to date. Of the 265 reviewed publications, 125 (49%) reported incidences of parasitism by subcutaneous Philornis, but only 12 included the sampling of adult breeding birds. Nine of these publications (75%) reported Philornis parasitism in adults of ten bird species. During fieldwork in the Dominican Republic, Puerto Rico, and Grenada, we documented 14 instances of parasitism of adult birds of seven avian species. From literature review and fieldwork, adults of at least fifteen bird species across 12 families and four orders of birds were parasitized by at least five Philornis species. In both the published literature and fieldwork, incidences of parasitism of adult birds occurred predominantly in females and was frequently associated with incubation. Although our findings indicate that Philornis parasitism of adult birds is more common than widely presumed, parasite prevalence is still greater in nestlings. In the future, we recommend surveys of adult birds to better understand host-Philornis relationships across life stages. This information may be essential for the development of effective control measures of Philornis to ensure the long-term protection of bird species of conservation concern.