Date of this Version
Locating nests of grassland passerines can be difficult, labor intensive, and disruptive to birds and vegetation. We developed a mobile tower blind for observing adult bird behavior and used it to locate nests in a western Montana grassland. We compared nest-search efficiency of behavioral observations from the tower versus the ground. Nests of savannah sparrow (Passerculus samhvichensis) were found in a higher proportion of territories searched from the tower (13/16 = 82%) than from the ground (4113 = 3 1%). Average search time for each nest found was lower from the tower (44 min) than from the ground (127 min). Both were lower than when we used drags made of rope or cable and chain (411 min). but nests were found earlier in the nesting cycle when we used drags. Adult birds were agitated and reluctant to approach and reveal their nests whenever an unconcealed observer was present in or near their territory. In contrast, normal behavior resumed within a few minutes after an observer entered the tower, even when the tower blind was within 10m of the nest. Observing behavioral cues from a tower blind provides substantial advantages for locating nests of savannah sparrows and probably other grassland birds. but effectiveness of the approach likely varies among species and habitats.