Burning the candle at both ends: two sympatric thrushes are equally detectable and sing at similar rates at dawn and dusk

How vocal activity varies between these two periods has not been examined in many species. In this study, we explored rates of detection and song rate of two sympatric passerines, Hermit (Catharus guttatus) and Swainson’s (Catharus ustulatus) thrushes, at dawn and dusk.

At three intervals in the breeding season, we examined eight 1-min intervals from 60-min before to 60-min after both sunrise and sunset. We recorded whether each species was detected, the total number of songs sung, and the number of individuals singing. We found that both Hermit and Swainson’s thrushes were equally likely to be detected at all time periods except that Hermit Thrush singing was reduced and Swainson’s Thrush song was absent 60-min after sunset.