Adult Great Gray Owl - How to Age It

5 March 2009

Adult Great Gray Owl at Holland Landing north of Toronto on 5 March 2009. Digiscoped from the road.


Close-up of wing and tail in photo 1

This adult is 2 1/2 years or older as indicated by three generations of secondaries: the oldest secondaries are faded with frayed edges, two are faded but not overly worn, and the newest are the darkest ones. Great Grays older than a year have some plain dark primaries as on this individual. Also note that some wing coverts and undertail coverts are skeletonized, i.e. worn to the feather shaft. The retention of considerable old feathering indicates an inhibited or partially skipped molt that probably resulted from food stress during the molt period before this owl irrupted southward. For more information on molts and aging Great Gray Owls see Pittaway and Iron 2005. Click on link below.