Responsiveness of Nesting Northern Goshawks to Taped Broadcasts of 3 Conspecific Calls

Kennedy, Patricia; Stahlecker, Dale

Because locating nest sites of forest-dwelling raptors is difficult and time-consuming, we determined if broadcasting conspecific vocalizations of northern goshawks (Accipiter gentilis; hereafter referred to as goshawks) increased goshawk detectability during the nesting season in northcentral New Mexico (NM) and northcentral Arizona (AZ). We recorded responses of goshawks to an observer who was either broadcasting alarm, wail, or juvenile begging calls, or was not broadcasting at all while walking transects. We sampled 215 transects at 27 goshawk nests during sampling periods associated with courtship, nestling, and fledgling-dependency periods during 1990. Goshawk responses to taped conspecific calls were higher (P = 0.02) than their responses to an observer without a tape. Detection rates were highest on transects with broadcasts during the nestling (73.3%) and fledgling-dependency periods (76.9%). During all sampling periods, the probability of detecting a goshawk was highest for observers broadcasting a conspecific vocalization within 100-200 m of the nest. During the nestling period, the alarm call elicited the highest detection rate, whereas the wail and begging calls resulted in the highest detection rate during the fledgling-dependency period. Vocal mimicry by Steller's jays (Cyanocitta stelleri; hereafter referred to as jays) (potential false positives) occurred on 16.7% of the transects. The lowest mimicry rates occurred during the nestling period. Our data suggest that goshawks are best surveyed with broadcast conspecific vocalizations during brood rearing at stations that are 300 m apart on transects that are separated by 260 m, and that stations on adjacent transects be offset by 130 m.

Responsiveness of Nesting Northern Goshawks to Taped Broadcasts of 3 Conspecific Calls

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