[CT Birds] Ageing and sexing Snowy Owls - a cautionary note

Julian Hough jrhough1 at snet.net
Sun Dec 22 11:48:26 EST 2013


I used to think I could age and sex some Snowy Owls. While I think the 
heavily barrd birds with boldly barred napes and minimal white "bibs" are 
females, and the lightly marked and almost white birds with broken tailbands 
are males, this isn't always the case.
Birds with vermiculated inner greater coverts and primary tips may be 
first-years (HY) but I'm not sure older birds cannot show these in 
successive moults, so it really is hard to age and sex birds of unknown age 
in the field.
Individuals often get lighter with age, stay the same, or get darker so 
there is a whole gamut of variation and overlap. Apparently according to 
Russian research, first borns in the nest are often paler than successive 
hatchlings which are darker!
Also, some HY males (aged in the hand from banding / specimens) may overlap 
with adult females and may only be differentiated by size. Pyle mentions 
tail (?) feather shape (blunt and rounded vs bluntly pointed) as a means of 
ageing some birds, but this seems hardly useful in the field.

The only main way of ageing Snowy Owls to calendar year (after HY/SY) is 
perhaps during June-September when birds have an incomplete primary moult 
and it MAY be possible to differentiate between old and new primaries.

I have seen few birds in New England I would call "females. This fits the 
migration pattern which basically is that females, being larger and 
dominant, take territory further north and it is the males that are "pushed" 
out further south. It also makes sense, from a probability point of view, 
that many of these birds are likely HY birds.

So, it seems from conventional wisdom that while we may think a bird is a 
young bird, or most likely a female (if large and boldy barred) we are 
likely guessing a lot more than we think we are.

Good owling.

Julian


Julian Hough
CT, 06519
USA
jrhough1 at snet.net

Blog: www.naturescapeimages.wordpress.com
website: www.JulianRHough.com





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