The age of an owl is determined by examining the patterns
of feather replacement on the wings. As a bird ages, it's feathers
become worn and faded, and are replaced with new feathers. If
the pattern and timing of feather replacement is know for a species,
then the age of a bird can be determined. During the fall, young
of the year (hatch year) Northern Saw-whet Owls have a full set
of new flight feathers, individuals over a year old have replaced
a portion of their flight feathers, but still retain some of the
feathers grown the previous summer, individuals over two years
old my have three generation flight feathers.
Photo by Ann Nightingale.
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