Auditory surveys for Northern Saw-whet Owls (Aegolius acadicus) in southern Wisconsin 1986-1996

Abstract

During auditory surveys with tape playback between 13 February and 27 April during 1986-1996, our detection of calling by Northern Saw-whet Owls (Aegolius acadicus) varied dramatically and regularly in an apparent 4-year cycle: 1986, 1990, and 1994 were significantly high calling years; 1987-1989, 1992-1993, and 1995- 1996 were significantly low; and 1991 was intermediate. Calling was also significantly affected positively by increasing time since sunset and negatively by date. Results from daytime searches during 1986- 1990 for saw-whet owl individuals, roosts, and pellets did not show annual fluctuation. Three other owl species were also heard during these auditory surveys. Calling by Eastern Screech-owls (Otus asio) was not significantly affected by any variable tested. Calling by Great Horned Owls (Bubo virginianus) was significantly affected by annual cycle and year, each with opposite effects than for the saw-whet owl. Calling by Barred Owls (Strix varia) showed no year or cycle patterns, but was negatively affected by date and wind, positively affected by increasing cloud cover, and positively correlated with saw-whet owl calling.

Parent Publication

• Biology and conservation of owls of the Northern Hemisphere: 2nd International symposium

Citation

Swengel, Ann B.; Swengel, Scott R. 1997. Auditory surveys for Northern Saw-whet Owls (Aegolius acadicus) in southern Wisconsin 1986-1996. In: Duncan, James R.; Johnson, David H.; Nicholls, Thomas H., eds. Biology and conservation of owls of the Northern Hemisphere: 2nd International symposium. Gen. Tech. Rep. NC-190. St. Paul, MN: U.S. Dept. of Agriculture, Forest Service, North Central Forest Experiment Station. 411-420.