[Birdtalk] Hawk-Owl age/sex info

[Cliff and Lisa Weisse]

I received a reply from Ryan Brady in WI regarding the age and sex of 
the Rexburg Northern Hawk-Owl.  The short version is it's probably a 
bird that was hatched this year and it's impossible to sex them in the 
field.  Adult Northern Hawk-Owls molt some, but not all, of their 
secondaries during summer and early fall so they would have secondaries 
of at least two ages.  This bird appears to have all flight feathers the 
same age, which would make it a juvenile that grew all its flight 
feathers this summer.  Here's what Ryan says:

"It's impossible, at least as currently known, to sex hawk owls of any 
age in field.  They don't show much size dimorphism compared with other 
raptors and no known plumage differences.  Aging them in the field is 
difficult without capture.   However, if I were a betting man, I would 
suggest your bird is a hatch-year individual.  Adults show incomplete 
secondary molt (late summer/early fall) and thus have multiple 
generations of secondary feathers.  Hatch-year birds have a complete set 
of uniform flight feathers (from hatching) showing fairly uniform wear 
patterns.  Darren's flight shot seems to show flight feathers of all the 
same age.  The two perched shots (Darren and Tim?), although difficult 
to tell for sure on a folded wing, seem to show the same thing.  I don't 
see any significant wear on the primaries but the tertials and inner 
secondaries are lighter brown and more worn than the rest of the wing.  
This is the result of more exposure, not because these feathers are 
older.  Furthermore, the innermost secondaries and tertials are among 
the first to be replaced during molt of SY birds and thus we might 
expect these worn tertials to be fresher on many adult birds.  Pyle's 
in-hand identification guide mentions some age differences in the 
rectrices but some friends and I captured many individuals during a big 
invasion several years ago and found no useful aging features in the rects."

Cliff

-- 
Cliff and Lisa Weisse
Island Park, Idaho
cliffandlisa at octobersetters.com