Rates of infestation by the scaley leg mite (Knemidokoptes jamaicensis) were examined on two overwintering Nearctic-Neotropical migrants, Palm Warbler (Dendroica palmarum) and Prairie Warbler (D. discolor), in low-elevation desert thorn scrub and high-elevation pine forest in the Dominican Republic. Ectoparasites were common on birds in the dry thorn scrub where birds roosted communally, but were never found on birds in the moister pine forest where communal roosting was not detected. Prevalence of ectoparasites varied between years and generally increased in prevalence within winters, with mean rates of infestation reaching as high as 25% among Palm Warblers in late-winter. Parasitized Palm Warblers showed significant decreases in mean pectoral muscle mass scores indicating a negative effect on body condition and physiological stress. Infestation had a significant effect on overwinter site persistence and annual return rates; no infected individuals ever returned the following year. Results of a path analysis indicated that mite infestation was more important than general physiological condition (as represented by pectoral muscle score) in determining annual return. Data suggest that environmental variables and host behavior may affect parasite infestation rates, and further attention should be given to the potential contribution of parasite infestation to winter limitation of avian populations.
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Vol. 120 • No. 3