Incidence and Effect of Hippoboscid Flies

House Finches in North America are known hosts of ectoparasitic hippoboscid flies and eastern finches are also susceptible to the eye disease mycoplasmal conjunctivitis. I used three years of trapping data from a population in Georgia to ask if birds affected by conjunctivitis had increased rates of hippoboscid fly parasitism. Of 1,531 examinations of 1 ,287 House Finches, hippoboscid fly prevalence was 0.89% in birds with no conjunctivitis and 0.95% in birds with conjunctivitis. These rates were not significantly different, but the overall low prevalence in this population was considerably lower than that reported in other eastern House Finches. Two individuals with both conjunctivitis and hippoboscid flies appeared to be in poor health. particular, the House Finch, has l>een examined in this respect more than most species (Wood 1983, McClure 1984). House Finches are native to western North America but were introduced into the eastern United States in the 1940s and have since spread to most eastern states, so that now two, non-overlapping House Finch populations, eastern and western, exist in North America (Hill 1993). With respect to their hippoboscid fly parasitism, Wood (1983), studying eastern House Finches, found an overall prevalence rate of 13%, and found that hippoboscid flies were present from June to September. McClure (1984) examined 9,973 western House Finches aver six years and observed an overall prevalence rate of 1.7%. McClure found hippoboscid flies on House Finches in all months of the year, but by far most occurred from June to October. INTRODUCTION In 1994, over a decade after these initial studies of hippoboscid parasitism in House Finches, House Bird banders have long known of hippoboscid Finches in eastern North America began contractflies-small, flattened, parasitic flies that live ing a newly emerged disease, mycoplasmal amongst the feathers of birds and often escape conjunctivitis (Fischer et al. 1997, Altizer et al. when birds are handled. These flies feed on the 2004a). This disease, caused by the bacterium blood of their host, and often can affect the conMycoplasma gallisepticum (MG), causes infected dition of their host negatively (Senar et al. 1994). individuals to develop easily recognizable sweiiHippoboscid flies· were once thought to be ings around their eyes (conjunctivitis) with facilitators of feather mite transfer between birds outbreaks occurring annually during the fall and (Jovani et al. 2001 ). Much of what is known about winter months (Altizer et al. 2004a, Altizer et al. hippoboscids comes from reports by bird banders. 2004b). Infected House Finches are not able to Since banders routinely handle large numbers of forage efficiently (Hotchkiss et a1. 2005) and have birds, they have been able to document the general poor body conditions (Altizer et al. 2004a). distribution and incidence of hippoboscid fly Furthermore, based on citizen-science data, parasitism on many landbird species (e.g. Wood Altizeret al. (2004b) showed that prevalence of this 1983, McClure 1984, Davis 1998). One species in disease was highest in the southeastern U.S. This Jul. Sep. 2007 North American Bird Bander Page 109 raises an interesting question: does this high conjunctivitis prevalence make this population particularly susceptible to parasitism by ectoparasites such as hippoboscid flies? This may be the case if conjunctivitis influences the House Finches' ability to preen and successfully rid themselves of