Barnes, Keith P. – Ecology, habitat use, and probability of detection of Flammulated Owls in the Boise National Forest. 2007.
Flammulated Owls (Otus flammeolus) are recognized as a sensitive species because of uncertain population viability and potential effects of anthropogenic manipulations of their ponderosa pine (Pinus ponderosa) forest habitat. During 2005 and 2006, I radio-tagged and monitored habitat use of 24 Flammulated Owls in central Idaho. I determined that owl densities in my study area were 0.34-0.43 territorial adult males/40ha. At the landscape level, owls selected south and east-facing aspects, middle to upper slopes and ridges, and areas of intermediate forest cover. At the home range scale, owls selected areas of higher density of standing dead trees (snags) but showed high variability in use of other forest characteristics. I did not detect selection for habitat characteristics at the scale of nest trees or vegetation surrounding nests. Owls selected large ponderosa pine trees for day roosts, and, when owls roosted in Douglas-fir (Pseudotsuga menziesii) trees, often they selected medium-sized trees. At scales below the landscape scale, it is possible that tolerance of a range of conditions has enabled Flammulated Owl populations to persist despite historical widespread alterations to their principle habitat of mature ponderosa pine forests.
Broadcasts of conspecific vocalizations are commonly used to increase detection rates on surveys of secretive bird species, yet the assessment of detectability necessary to fully interpret such survey data is frequently lacking. I evaluated the probability of detection of 17 radio-tagged male Flammulated Owls (Otus flammeolus) to conspecific broadcast surveys in Idaho during 2005 and 2006. Probability of detection was 100% during the pair-bonding and incubation periods of the breeding season, after which time it declined to a low of less than 15% during the post-fledging period. Paired males showed a different pattern than unpaired males. Following hatching of eggs, detectability of paired males declined gradually over a 6-week period while detectability of unpaired males dropped sharply for a 4-week period before increasing during the post-fledging period for paired owls. Surveys for Flammulated Owls should be conducted during the pair-bonding and incubation periods, during which time high detectability permits inference of presence or absence of owls from broadcast survey detections.