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11 November 2019 Ageing Northern Saw-Whet Owls (Aegolius acadicus) from Remigial Molt Patterns
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Abstract

We recorded molt patterns of migrant Northern Saw-whet Owls (Aegolius acadicus) at three locations in the Great Lakes region: Stevens Point, Wisconsin; Whitefish Point, Michigan; and Duluth, Minnesota. We then analyzed the molt patterns of recaptured birds that were banded in a previous season and originally classified as hatch-year birds (i.e., they had no remigial molt). Of these 286 known-age birds included in our analysis, 155 (54%) were second-year (SY), 72 (25%) were third-year (TY), 39 (14%) were fourth-year (4Y), 16 (6%) were fifth-year (5Y), three (1%) were sixth-year (6Y), and one (0.30%) was eighth-year (8Y). Using these known-age birds, we were able to identify definitive molt patterns for the SY and TY age classes. All 155 (100%) SY birds and 52 (72%) of the TY birds matched our ageing criteria. The remaining 28% of TY birds did not match our ageing criteria and were classified as after-second-year (ASY). Of the entire sample (n = 286), only three birds (1%) matched an incorrect age class, including one 4Y that matched the SY age class and two 5Y that matched the TY age class.

© 2019 The Raptor Research Foundation, Inc.
Nova Mackentley, Eugene A. Jacobs, and David L. Evans "Ageing Northern Saw-Whet Owls (Aegolius acadicus) from Remigial Molt Patterns," Journal of Raptor Research 53(4), 387-392, (11 November 2019). https://doi.org/10.3356/0892-1016-53.4.387
Received: 28 November 2018; Accepted: 16 July 2019; Published: 11 November 2019
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