INTRODUCTION: Many birders have asked us questions about (1) distinguishing
the ages and plumages of Great Gray Owls and (2) how to tell males from
females. Most of the differences seen in the field are due to individual
variation. After September, the young of the year (three months of age) and
older birds are very similar in appearance. However, two broad age classes
can be recognized in the field with practice. Here we describe how to tell
first year birds (hatched in 2004) from adults (older birds) using links to
photos. We hope that birders and those doing surveys will use this
information to better understand the numbers of first year and adult birds
in this winter's irruption. If you are taking photos of perched birds to
determine age, the best ones are of the sides and back showing the
wingtips, secondaries, wing coverts and tail.
MALE or FEMALE: Females are larger than males, but there is considerable
overlap. Judging size in the field is deceptive and unreliable. If several
birds are seen together, one might "guess" that an extremely small
individual is a male or an extremely large one is a female, but not with
much certainty.
SUBSPECIES: There is one subspecies (race) in North America, which is the
nominate (first named) race Strix nebulosa nebulosa. The Great Gray Owl was
first described in 1772 from the Severn River in northern Ontario. It is
one of the few bird species first described from the New World that also
occurs in the Old World. One other subspecies occurs across northern
Eurasia; its scientific name is S. n. lapponica. The Royal Ontario Museum
specimens of lapponica are slightly paler overall with more distinct long
streaks below. A third subspecies, S. n. elisabethae, described from
Mongolia is not recognized by most authorities.
MORPHS: There are no morphs (correct term for phase) of the Great Gray Owl.
Some birds are greyer or browner than others due to wear, faded older
feathers and individual variation. The same bird will appear different
depending on light, time of day, and background. A bird's true colours and
patterns are often altered in photographs.
ALBINOS: Albinism is more frequent in Great Gray Owls than in other North
American owls. A pure white bird in Idaho mated with a normal bird produced
normal young. Partial albinos and leucistic birds with diluted plumage
coloration have been recorded.
MOLT: Juveniles complete a partial molt into first year (first basic)
plumage by late September. First year birds retain the juvenile primaries,
secondaries, and tail for more than a year. The flight feathers of first
year birds appear about the same colour and contrast because they are the
same age. The first molt of flight feathers starts about 13 months of age.
Not all primary/secondary feathers and often lesser secondary coverts are
molted annually, so after about 1.5 years of age, they show a mix of older
faded brown and new darker flight feathers. A few juvenile
primary/secondary feathers may be retained for several years. Most birds
molt their tail feathers every year. Note: Older feathers wear and fade to
brown providing a molt contrast with newer feathers, which is very useful
in aging.
AGES: Two broad age classes can be identified in the field: (1) First year
birds hatched in 2004 and (2) adults.
FIRST YEAR: First year birds have pale tipped primaries and secondaries,
except on the short 10th outer primary which lacks a pale tip. The tail
feathers of first year birds often have a tiny sharp point where the
juvenile down adhered to the tips of tail feathers; these tips remain into
January or February. First year birds lack a mix of older browner feathers
from previous years often found on adults. Note: We have seen very few
first year Great Gray Owls this winter suggesting a poor breeding season in
2004.
ADULT: The folded wingtips are dark brown (no pale tips) and contrast
darker with the grey tertials above. A mix of pale primary tips and adult
tips suggests a 2-3 year old bird. The central tail feathers of adults are
wider with more rounded tips. On some adults one or two new grey
secondaries contrast among brownish secondaries on the folded wing. The
plumage of adults often shows a mix of older browner feathers contrasting
with the greyer new plumage. Note: Most of the Great Gray Owls that we have
seen this winter have been adults.
CAUTION: The above information on aging Great Gray Owls is preliminary.
Many are difficult if not impossible to age in the field. If you have
comments or additional information, please email us at <[EMAIL PROTECTED]>.
PHOTO LINKS with remarks on aging.
1. http://www3.sympatico.ca/jeaniron/AgingGrGr2.htm Two photos comparing
folded wingtip patterns of first year and adult.
2. http://www3.sympatico.ca/jeaniron/AgingGrGrays.htm Three photos
comparing first year and adult birds.
3. http://www.ofo.ca/photos/greatgrays/ Top row, left photo: Dark folded
wingtips with no pale tips indicate an adult. Second row, right photo:
Pointed tail tips indicate a first year bird.
4. http://www.ofo.ca/photos/greatgray/ Photos from OFO's website: Top row,
left photo (Sept 22). Down still adhering to head feathers indicates a
first year bird. Second row, left photo (Nov 7). Dark wingtips lacking pale
tips and brownish secondaries contrasting with tertials indicate an adult.
Dark wingtips on Oct 16 (top right) and Nov 26 (bottom) birds also indicate
adults.
5. http://www.greenbackedheron.com/id.cfm?setid=1234 Four photos from Kent
Nickell's website. Third bird is an adult because of dark wingtips lacking
pale tips, old brownish secondaries and contrasting brownish wing coverts.
Fourth bird is an adult because it has dark wingtips lacking pale tips,
brownish secondaries and a contrast of older brown feathers among the newer
grey body feathers.
ACKNOWLEDGEMENTS: Mark Peck and Glenn Murphy allowed us to examine
specimens at the Royal Ontario Museum. We thank Michel Gosselin of the
Canadian Museum of Nature for advice. Ron Tozer made helpful suggestions.
REFERENCES used for this article and for more information.
Brunton, D.F. and R. Pittaway. 1971. Observations of the Great Gray Owl on
winter range. Canadian Field-Naturalist 85:315-322.
Bull, E. L. and J. R. Duncan. 1993. Great Gray Owl (Strix nebulosa). In The
Birds of North America, No. 41 (A. Poole and F. Gill, Eds.). Philadelphia:
The Academy of Natural Sciences; Washington, D.C.: The American
Ornithologists Union.
Duncan, Jim. 1996. Techniques to Sex and Age Great Gray Owls: a bird in the
hand worth two in the bush? Birders Journal 5(5):240-246.
Godfrey, W. Earl. 1986. The Birds of Canada. National Museums of Canada,
Ottawa.
Nero, Robert W. and Herbert W.R. Copeland. 1997. Sex and Age Composition of
Great Gray Owls (Strix nebulosa). In Duncan, James R.; Johnson, David H.;
Nicholls, Thomas H., eds. 1997. Biology and conservation of owls of the
Northern Hemisphere: 2nd International symposium; 1997 February 5-9;
Winnipeg, MB. Gen. Tech. Rep. NC-190. St. Paul, MN: U.S. Department of
Agriculture, Forest Service, North Central Research Station. 635 p.
Pyle, Peter. 1997. Identification Guide to North American Birds. Part 1.
Slate Creek Press, Bolinas, California.
Please allow Great Gray Owls the space they need to hunt and rest. To age
them, a scope is essential.
Ron Pittaway and Jean Iron
Minden and Toronto, Ontario
[EMAIL PROTECTED]
