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    Over the past 17 years, research on a rain forest population of the Pearly-eyed Thrasher (Margarops fuscatus), with additional observations on nesting Puerto Rican Parrots (Amazona vittata) within the Sierra de Luquillo, Puerto Rico, has shown that reproductive success of thrashers and parrots is often greatly reduced as a result of the additive effects of a diverse group of predators, competitors and ectoparasites, namely, other thrashers, Puerto Rican Screech-Owl (Otus nudipes), scansorial black rat (Rattus rattus); honeybee (Apis mellifera ligustica and A. m. scutellata), and a muscid botfly (Philornis sp.). Although egg and chick losses from nest predators and competitors accounted for less than 10%, botfly ectoparasitism was responsible for 56% of the remaining chick losses. This research not only summarizes the prevalence and intensity of nest predation and ectoparasitism but, more importantly, addresses the interaction between these two forms of biological control. Such knowledge is preeminent in managing endangered species and their biological stressors. Results from Pearly-eyed Thrasher research show that predation rates, nest-site competition, and the prevalence and intensity of botfly ectoparasitism at thrasher nest boxes varied significantly among years and months, increased with the progression of the thrasher breeding season, and escalated following major habitat disturbance. Primary nest predators of the thrasher and parrot have developed a strategy of taking their prey just before the hosts’ average age at death resulting from Philornis ectoparasitism, thus increasing the predators’ chances of success. At thrasher nest boxes, instances of predation, cavity takeovers, and the prevalence and intensity of botfly ectoparasitism are highly correlated with each predator’s, competitor’s, and ectoparasite’s own breeding seasons which, when combined, span the entire reproductive period of both the thrasher and parrot. The breadth and extent of the predatory and parasitic habits of the Puerto Rican Parrot’s five main biological stressors show that constant, intensive nest guarding, poisoning and trapping (rats), and repellents (against honeybees and botflies) are necessary in recovery efforts. Management recommendations and additional parrot research needs are offered as possible steps in ameliorating the effects of these nocuous organisms so detrimental to the Puerto Rican Parrot’s recovery.

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    Arendt, Wayne J. 2000. Impact of nest predators, competitors, and ectoparasites on Pearly-eyed Thrashers, with comments on the potential implications for Puerto Rican Parrot recovery. Ornitologia Neotropical. 11:13–63,


    Amazona vittata, Apis mellifera, biological control, black rat, botfly, ectoparasitism, honeybee, ligustica, Margarops fuscatus, nest predation, Otus nudipes, Pearly-eyed Thrasher, Philornis, Puerto Rican Parrot, reproductive success, Screech-Owl, scutellata.

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