Alaska Bird ObservatoryAlaska Bird ObservatoryPREPARED FOR: Brad Andres USFWS Migratory Bird Office, 1011 E. Tudor Rd., Anchorage, Alaska, 99503-6199.
PREPARED BY: Anna-Marie Benson, Alaska Bird Observatory, P.O. Box 80505, Fairbanks AK, 99708 (ambenson@alaskabird.org)
Boreal Partners in Flight members conducted owl surveys during spring of 2000. These surveys were conducted as part of a preliminary investigation into the effort required to develop a long-term owl monitoring protocol in Alaska. Our objective here is to summarize the data collected on owl surveys in Alaska during 2000. We also examine the daily variation in singing phenology.
METHOD
Owl surveys were conducted in Alaska from 22 March to 29 April 2000. Survey locations were selected based on several criteria: accessibility, low levels of human disturbance, and expectations of high numbers of owl detections. Point-count stations were spaced 0.5 mile to 1.0 mile apart and observers drove between stops. Visual and auditory cues of owls were recorded during 8-minute periods. Weather variables were recorded and surveys were not conducted in adverse weather conditions. Surveyors also recorded distance (and usually direction) to the owl. Owls that may have been double counted were removed from this compilation.
Several routes were repeated more than once to examine the seasonal and daily variation in singing phenology. We determined whether detections were disproportionately high within days by comparing the number of owl detections to the expected number of detections based on survey effort.
We grouped surveys from throughout Alaska for this compilation because low sample sizes prevented a more refined grouping of biogeographic areas. These results may therefore be confounded by the geographic variation among owl populations within Alaska.
RESULTS
Twenty routes were surveyed in Alaska during 2000 (Table 1). Many of these routes were repeated more than once, with one route surveyed 14 times. A total of 776 points were surveyed and 57 Great-horned Owls, 31 Boreal Owls, and 26 Saw-whet Owls were detected (Table 1). Additionally, a pair of Great Gray Owls was detected on the Murphy Dome route in Fairbanks on two different days, and one Short-eared Owl was detected on the Steese Route, near Fairbanks.
On most routes, few or no owls were detected even if the route was repeated several times. Only 26% of all detections were recorded on 85% of the routes. The Aleknagik, Fort Greely, and Hope surveys had the most detections of owls; these surveys comprised 15% of all of the surveys conducted in Alaska, yet 74% of detections were recorded on these routes.
We did not make inferences about the peak singing periods of owls within the season because surveys only sampled a one-month period; however, Figures 1 and 2 provide a description of surveys conducted and number of detections. Repeating surveys did not seem to increase the number of detections associated with most routes.
Peak detection periods were 2-5 hours after sunset (Fig. 3); however, all dark hours were not sampled evenly, i.e., most points were surveyed 2-5 hours after sunset (Fig. 4). Boreal Owls were detected most frequently 4-5 hours after sunset, this difference was significantly different from the expected number of detections based on survey effort (X2=17.9, df=6, P<0.01). There was no difference in times that Great Horned Owls were detected compared with expected number of detections based on survey effort. Saw-whet Owls were detected in disproportionately high numbers in the 5-6 hours-after-sunrise category (X2=23.2, df=6, P<0.001).
DISCUSSION
Several owl surveys were conducted throughout Alaska during 2000, but few owls were detected on 17 of 20 routes. Several factors could explain the low numbers of owls counted on most surveys. First, densities of owls may be extremely low in most parts of Alaska, indicating a large number of surveys would be required to have adequate sample sizes to determine long-term trends in detections of Boreal Owls and Great Horned Owls in Alaska. Second, owl densities may fluctuate from year to year; perhaps densities were lower than average in 2000 in areas where surveys were conducted. Third, our non-random sample of surveys may have created a bias toward low density of owls near population centers. Finally, the survey period may not have adequately sampled the peak singing periods for owls, i.e., surveys may have been conducted too late.
RECOMMENDATIONS
1. Repeat survey routes that have potential for long-term monitoring.
2. Avoid establishing surveys near towns.—Two routes in Fairbanks (Murphy Dome and Goldstream) were problematic because noise from dog teams and cars distracted surveyors. These two surveys will not be conducted in future years.
3. Begin surveys on 15 February, rather than 15 March, to determine whether more individuals could be detected earlier in the year.
4. More study is needed to determine whether singing males adequately represent abundance of owls in Alaska.
ACKNOWLEDGEMENTS
We would like to thank Brad Andres, USFWS Migratory Bird Management, for gathering funds for this compilation. Thanks to the many agency biologists whom contributed the survey data herein: Buddy Johnson (USFWS), Jeff Mason (Colorado State University), Deb Nigro (NPS), Susan Savage (USFWS), Rob MacDonald (ADFG), and Stacy Prosser (USFS). Many thanks to David Shaw (ABO) for entering and maintaining records and convincing many volunteers to conduct surveys: Amal Ajmi, Michelle Ambrose, Laurel Devaney, Adia DeWitt, Dana Durham, Catherine Egan, Greg Egan, Rebecca Gilbert, Lorrie Hawkins, Brita and Janlee Irving, Sherry Lewis, Jim Logan, Tony Payne, Joyce Potter, Mark Ross, Ken Russell, Kristine Sowl, and Judy Williams.
©2000 Alaska Bird Observatory, Inc.
All rights reserved
Limited permission is granted to educators to reproduce these materials for use by their students
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