Nesting biology of the Tennessee Warbler, Vermivora peregrina, in northern Ontario

Abstract

Fourteen Tennessee Warbler, Vermivora peregrina, nests were monitored during the 1994 breeding season near Longlac, Ontario. Videocameras were used to record various aspects of parental care. In our study area, Tennessee Warblers nested in relatively dry, open areas. The edges of old logging roads and small clearings were favoured nesting locations. The nests were well concealed. Cover was provided by a variety of ground plants, in particular mosses, grasses, Bunchberry and Large-leaved Aster. The median clutch size of 11 nests was 6 eggs (range 5 to 7). Hatching success was 94%. The median brood size of 14 nests was 6 nestlings (range 4 to 7). The interval from the laying of the last egg to the hatching of the first nestling was 7-8 days. This is exceptionally short compared to that of other warbler species. A short incubation period may be an adaptation that allows the species to take maximum advantage of a pulsed food supply (i.e., Spruce Budworm) for nestling growth and development. The Mayfield estimate of nest success for Tennessee Warblers in this study (73.3%) was high compared to other ground-nesting songbird species. Male Tennessee Warblers provisioned their nestlings at higher rates than did their mates, especially during the first few days of nestling life. Feeding rates increased with increasing nestling age and brood size. Lepidoptera larvae and pupae were the most common food items in the diets of nestlings.