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 conditio ns indexed by birds. Therefore, it is important to quantify periods of bird activity so biologists can plan studies. We determined hourly detections f rom singing males of 22 nongame bird species in ponderosa pine, quaking asp en, and grassland vegetation types in the Black Hills of South Dakota. Dete ctions of 12 of 22 species differed among 1-hr intervals after sunrise. Det ections of yellow-rumped warblers, Townsend's solitaires, red-breasted nuth atches, western tanagers, and American robins decreased on count-episodes m ore than 4 hrs after sunrise. Detections of dusky flycatchers declined on c ount-episodes more than 3 hrs after sunrise and detections of black-capped chickadees were greatest during the first hour after sunrise and declined a fterward. Detections of many other species from songs or calls decreased on count-episodes more than 5 hrs after sunrise. We recommend that bird count s in the Black Hills be completed within 4 hrs after sunrise so estimates o f bird abundance are not affected by reduced singing among males.