Factors affecting the detection of elf owls and western screech owls
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Although elf owls (Micrathene whitneyi) and western screech owls (Otus kennicottii) are of management interest because of their potential to serve as barometers of environmental change, factors affecting the detection of these species have not been quantified. We conducted point counts for elf owls and western screech owls from 1994 to 1996 in the Sonoran Desert, southwestern Arizona. We assessed whether owls were more detectable when broadcasts were used than when they were not, and how temporal, lunar, weather, and biological variables affected detection rates. We assessed factors that potentially varied within a night (weather, time, presence of other owls) separately from those that did not vary within a night (date, moon phase). Elf owls and western screech owls were more likely (P < 0.001) to be detected when conspecific broadcasts were used than when broadcasts were not used. Within the breeding season, detection rates of elf owls were greatest during the late advertising period (11 April to 30 April) between the first-quarter and third-quarter moon phases. Detection rates of screech owls did not differ among moon phases or dates (P > 0.40). Controlling for moon phase and date, elf owls were most frequently detected during calm (wind < 5 mph), moonlit conditions. Increased detection rates of western screech owls were associated with decreased wind speed, temperature, and cloud cover. We recommend that conspecific broadcasts be used during surveys to increase detection rates for both species. Elf owls should be surveyed during the late advertising period between the first-quarter and third-quarter moon.
