Effectiveness of Call-broadcast Surveys to Detect Territorial Peregrine Falcons

—We developed and tested a 10-min call-broadcast survey protocol using conspecific vocalizations to assess Peregrine Falcon (Falco peregrinus) territory occupancy in the Mojave Desert of southern Nevada and northwestern Arizona from 2008–10. Response rate of peregrines, when adults were confirmed present immediately prior to broadcasting, averaged 83% during the breeding season and peaked at 100% during the courtship stage. Detection trials conducted at known occupied territories, when peregrine locations were unknown at the time of the broadcast, resulted in an average 78% detection rate across the breeding season, as compared to a 79% detection rate using the 4-hr default passive survey protocol from 2006–09. We detected peregrines in 42% of broadcast trials during the post-breeding period (September–October) in 2009. We did not observe differences in response rates related to time of day or distance from the broadcast point to the eyrie (85–1600 m). All peregrine responses during detection trials occurred within 300 sec after beginning the call-broadcast, and the mean duration of response by breeding stage diminished as the breeding season progressed. Response rates were similar by sex (male 5 60%, female 5 66%), but males were more likely to respond with females than alone. Peregrines often responded in the vicinity of eyries (72% of responses), a behavior we found useful for identifying eyrie ledges early in the breeding season. We found that conducting 10-min call-broadcast trials early in the peregrine breeding season at distances #700 m from the eyrie provided an effective means to assess