Hayes, Christine – Avian Myiasis and the Conservation of the Critically Endangered Ridgway’s Hawk (Buteo ridgwayi) of Hispaniola

Christine Hayes in the field
Christine Hayes in the field

Myiasis, the infestation of living tissue by fly larvae, has been confirmed to cause death in nestling birds and may be the driving force to the extinction of some bird species, especially those endemic to tropical islands such as the Galápagos (Plath 1919, Arendt 1985a, 1985b, Delannoy and Cruz 1991, Koop et al. 2011, 2015, Knutie et al. 2014). Bird-parasite interactions have historically been understudied (Loye and Zuk 1991) and we are only just beginning to understand some of the relationships between flies that cause avian myiasis and their hosts (Arendt 1985a, Dudaniec and Kleindorfer 2006, Rabuffetti and Reboreda 2007, O’Connor et al. 2010, Kleindorfer et al. 2014, Knutie et al. 2015, Koop et al. 2015). Because the reasons for the decline of many island endemic bird species in the Neotropics are incompletely known, improving our understanding of host-parasite relationships may be critical to restoring threatened and endangered species.

The genus Philornis (family Muscidae), a Neotropical Dipteran, contains ca. 50 described species, twenty of which have larvae that are known parasites of birds. (Dudaniec and Kleindorfer 2006, Antoniazzi et al. 2011, Quiroga and Reboreda 2013). The majority of the parasitic Philornis described, ca. 18 species, have subcutaneous dwelling larvae that are hypodermic burrowers, living just under the skin or within the muscle tissues of their hosts (usually nestlings) feeding on blood, tissue, and other body fluids, then dropping into the nest material to pupate (Dudaniec and Kleindorfer 2006, Antoniazzi et al. 2011). Few studies have described the biological relationship between Philornis and their hosts and no study has yet examined the ecological determinants and consequences of a host-parasite relationship for Philornis and any species of raptor.

Ridgway's Hawk (Buteo ridgwayi) chicks
Ridgway’s Hawk (Buteo ridgwayi) chicks
Ridgway's Hawk (Buteo ridgwayi) of Hispaniola
Ridgway’s Hawk (Buteo ridgwayi) of Hispaniola

The Ridgway’s Hawk (Buteo ridgwayi) is a socially monogamous, small forest Buteo, most closely related to the Red-shouldered Hawk (Buteo lineatus) of North America (Amaral et al. 2009). The Ridgway’s Hawk is a critically endangered raptor endemic to the island of Hispaniola with an estimated breeding population of 300 individuals, now isolated to Los Haitises National Park in the Dominican Republic (Thorstrom et al. 2005; Birdlife International, 2013). Historically, the Ridgway’s Hawk was common on the eastern third of Hispaniola, as well as on several satellite islands off of the western coast (Cory 1883, Wetmore and Swales 1931, Wetmore and Lincoln 1934, Wiley and Wiley 1981). At least one subcutaneous burrowing species of Philornis, P. pici, exists in the Dominican Republic (Macquart 1853) and infestations have been recorded in Ridgway’s Hawks, although the ecological relationship between these two species is yet to be described (Wiley and Wiley 1981, Woolaver 2011). Koop et al. (2015) found that small changes in botfly prevalence can have a major impact on avian productivity and survival at the population level for Darwin’s Finches in the Galápagos. If we can understand the ecological correlates of Philornis infestation in the Dominican Republic and manage them to reduce fly numbers, we can possibly have a substantial positive impact on the Ridgway’s Hawk population.

Christine holding a Ridgway's Hawk (Buteo ridgwayi)
Christine holding a Ridgway’s Hawk (Buteo ridgwayi)

The aims of my study are 1) to reveal whether or not Philornis infestation of nestling Ridgway’s Hawks negatively impacts hawk reproductive success and 2) to understand the environmental factors associated with high levels of Philornis intensity in Los Haitises National Park so that we can mitigate them.

Christine holding a Ridgway's Hawk (Buteo ridgwayi) P.S. if you look closely you can see a lizard tail sticking out of the nestling's mouth!
Christine holding a Ridgway’s Hawk (Buteo ridgwayi) P.S. if you look closely you can see a lizard tail sticking out of the nestling’s mouth!



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