Mills, Todd R., Rumble, Mark A. and Flake, Lester D. 2000. Optimum Timeframes for Detecting Songbird Vocalizations in the Black Hills.
Birds are indicators of vegetation structure and ecological conditions. The singing activity of birds declines during late-morning periods, which can affect estimates of abundance and conclusions regarding vegetative conditions indexed by birds. Therefore, it is important to quantify peridos of bird activity so biologists can plan studies. We determined hourly detections from singing males of 22 nongame bird species in ponderosa pine, quaking aspen, and grassland vegetation types in the Black Hills of South Dakota. Detections of 12 of 22 species differed among 1-hr intervals after sunrise. Detections of yellow-rumped warblers, Townsend's solitaires, redbrested nuthatches, western tanagers, and American robins decreased on count-episodes more than 4 hrs after sunrise. Detections of dusky flycatchers declined on count-episodes more than 3 hrs after sunrise and detections of black-capped chickadees were greatest during the first hour after sunrise and declined afterward. Detections of many other species from songs or calls decreased on count episodes more than 5 hrs after sunrise. We recommend that bird counts in the Black Hills be completed within 4 hrs after sunrise so estimates of bird abundance are not affected by reduced singing among males.