Recent analyses suggest that exposure to cholinesterase (ChE)-inhibiting pesticides may be a factor contributing to declines of white-winged dove (Zenaida asiatica) populations in the Lower Rio Grande Valley (LRGV) of Texas, USA. Because irrigated cotton fields are regularly sprayed with organophosphorus (OP) pesticides (known ChE inhibitors) and doves drink irrigation water, we conducted a series of experiments to determine effects of OP pesticides in drinking water on productivity and reproductive behavior of white-winged doves. During the breeding seasons of 1996-1998, we exposed captive breeding pairs of white-winged doves to various concentrations of methyl parathion (MP), an OP pesticide widely used in the LRGV. Exposure to drinking water with 1.0 ppm MP did not significantly affect reproduction. Exposure to ≥4.5 ppm MP primarily affected egg laying and incubation stages of the reproductive cycle. Specifically, both chronic and periodic exposure to MP-contaminated water reduced number of eggs laid/pair, time incubating, and number of chicks fledged/pair. Food and water consumption declined with exposure to MP. Responses of white-winged doves to MP exposure were consistent with the hypothesis that declines in dove populations in the LRGV are influenced by pesticide exposure. However, field evidence of direct exposure is required to support the hypothesis of a pesticide-related decline.