eWestern Birds
The Quarterly Journal of Western Field Ornithologists
Molt Sequences in an Extralimital Great Gray Owl Detected over Two Winters in Northwestern California
Rodney B. Siegel, Peter Pyle, and Helen L. Loffland
ABSTRACT: In California, the Great Gray Owl (Strix nebulosa) has a very small population and is considered endangered. The Coast Range of northwestern California is not considered part of the species’ regular range, and prior to January 2016 there were only three records for the region. During the winters of 2015–2016 and 2016–2017, however, a Great Gray Owl occurred in Humboldt County at locations separated by about 50 km. We evaluated photographs from both winters to assess whether they were of the same individual owl. Patterns of retained juvenile wing feathers and replaced feathers of the definitive basic plumage were consistent with the owl photographed in winter 2016–2017 (likely in its fourth cycle) being one year older than the one photographed in winter 2015–2016 (likely in its third cycle). Furthermore, during both years, the same primary feather on the right wing showed an irregularity along the inner web near the tip, including a notch and additional damage to the barbs, evidence that the observations in both years were of the same individual. Feather-replacement patterns in this individual during these two winters, along with those of another specimen from Humboldt County from 2007, imply that the sequences of molt of the remiges in the Great Gray Owl parallel those of other Strix but that the rate of molt may be slower than previously reported.