Nesting success, nest sites, and parental care of the least flycatcher in declining maple forests

Abstract

We compared nesting success, nest site characteristics, and parental care of the least flycatcher (Empidonax minimus) between healthy and declining sugar maple (Acer saccharum) stands in southern Quebec, from 1987 to 1989. On average, decline had caused a 20–30% foliage loss. A previous study showed that the least flycatcher was the most abundant species in these stands, even though some negative correlations between population densities and the intensity of decline were detected. Nesting success averaged 53% and did not differ between healthy and declining sites. Nests were located in larger trees in declining sites, and foliage loss in the canopy above the nest was twice as high as in healthy sites. Nestling feeding frequency was significantly higher in declining sites than in healthy ones. Mean meal size did not differ between sites, suggesting that nestlings received more food in affected stands in spite of evidence of lower insect abundance. The nestling diet was principally composed of Lepidoptera, Diptera, Hymenoptera, and Coleoptera in declining and healthy sites. Parents spent more time at the nest in declining sites in 1988, presumably because of increased brooding demand resulting from cold weather that year. We suggest that nestlings were thermally stressed in declining sites because of canopy foliage loss and that parents had to work more (i.e., provide more feeding and brooding) to maintain breeding success. Therefore, even though a moderate level of decline does not affect nesting success, flycatchers may still be negatively affected in more subtle ways.