Abstract
Three Northern Mockingbirds (Mimus polyglottos) and one Curve-billed Thrasher (Toxostoma curvirostre) from the Rolling Plains of Texas, USA were sampled for eyeworms in September 2013. All four birds were infected with the eyeworm Oxyspirura petrowi.
Oxyspirura petrowi is a heteroxenous nematode that occurs in numerous avian species (Pence 1972). Much of the recent attention on eyeworms has been on their potential role in the long-term decline of Lesser Prairie-chicken (Tympanuchus pallidicinctus; Robel et al. 2003) and Northern Bobwhite (Colinus virginianus; Villarreal et al. 2012) populations.
Northern Mockingbirds (Mimus polyglottos) and Curve-billed Thrashers (Toxostoma curvirostre) were often found feeding in or around ground traps used during a Northern Bobwhite study on a large ranch in the Rolling Plains of Texas, USA. Eyeworms were found in greater than 90% of bobwhites trapped on the ranch (Dunham et al. 2014). Three Northern Mockingbirds and one Curve-billed Thrasher were captured using double-funnel, welded wire, walk-in traps (91.4×61.0×20.3 cm) baited heavily with milo. Upon euthanizing and examining the birds, we recovered 13 eyeworms in the three Northern Mockingbirds and seven eyeworms in the Curve-billed Thrasher. The parasites were identified as O. petrowi, the first known reporting of O. petrowi in both species.
All birds were trapped and handled under Texas Parks and Wildlife permit SRP-1098-984, USFWS permit MB014265-0, Texas A&M University AUP 2011-193, Texas Tech University ACUC 11049-07, and Texas Tech University ACUC 13027-03. Voucher specimens of O. petrowi (Northern Mockingbird: 107285, Curve-billed Thrasher: 107286) were deposited in the US National Parasite Collection, Beltsville, Maryland.
There was no evidence of gross pathology in Northern Bobwhites, despite heavy infection of O. petrowi in the nasal-lacrimal-orbital tissue accompanied by spot hemorrhaging and inflammation (Dunham et al. 2014). This same report documented eyeworms attached to tissue, which suggests they were ingesting blood. Oxyspirura mansoni, which is primarily found in domestic poultry, can cause severe pathologic effects such as an inflammatory response, corneal opacity, nasal discharge, and eventual blindness in domestic poultry (Schwabe 1950). With these pathologic responses reported, it seems evident that eyeworms can potentially cause airway and visual obstruction, blood loss, and energy depletion, all of which will impair a bird's ability to fly, find or secure food, and ultimately impact its survival.
Both the Curve-billed Thrasher and Northern Mockingbird migrate, which gives them the ability to spread the eyeworms to areas of the world where they had not previously occurred. Oxyspirura petrowi has been found in cold northern climates including Minnesota (Erickson et al. 1949) and in very hot climates such as in Iraq (Al-Moussawi and Mohammad 2013). With the resilience of O. petrowi and the threat of potential spread of infection in migratory birds, eyeworm infections could become more frequent in regions where they historically have not been found. Further research is needed on the life cycle of the eyeworm so that treatment and control methods can be developed to reduce opportunities for infection in other avian species.