Food Availability Fails to Explain Asynchronous Breeding of Two Syntopic Oriental Trogons

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Seasonal variation in food supply may not adequately explain avian breeding phenology in tropical areas with relatively stable climates. In northeastern Thailand the Red-headed Trogon (Harpactes erythrocephalus) and Orange-breasted Trogon (H. oreskios) share similar nest sites, diets, foraging habitats, and foraging techniques but differ in timing of reproduction even though their food supply of insects varies in a similar seasonal pattern, peaking in June for both species. For the Red-headed Trogon, egg laying lasts 5–6 months and peaks in May; nestling provisioning coincides with peak food availability. For the Orange-breasted Trogon, by contrast, egg laying lasts 2–3 months and peaks in February. This nesting period is shorter and earlier than that of most other species of birds at our study site, and nestling provisioning preceded the period of peak food by 4 months. Timing of breeding by the Orange-breasted Trogon may represent a compromise between breeding at the optimal time based on food resources and avoiding competition for nest sites from the larger Red-headed Trogon.