Tuesday, October 20, 2009

Ageing Canada Geese

Determining the age of a goose can be helpful for identification, and can also reveal some interesting behavioral and ecological information by enabling you to sort out family groups and subflocks. Given good views it's not hard to distinguish Canada Geese that are still in juvenal plumage from those that are in adult plumage. By October many immatures (hatched in the summer a few months earlier) will have molted most of their body feathers into adult-like plumage, while others have not yet begun to molt. In general, consistent with other species of birds, the late-molting juveniles are long-distance migrants from far northern breeding grounds, while local Lower-48 resident Canada Geese molt in early fall.

Juvenile (top) and adult (bottom) Canada Goose. 19 Oct 2009. Concord, MA. Photos copyright David Sibley.

Differences apparent in these photos are:

  • Juvenile overall has lower contrast markings, especially blurry and obscure pale edges on back feathers
  • Juvenile has all feather tips narrow and rounded, vs adult feather tips broader and more square or flat-tipped. This creates a strongly barred pattern on the adult with pale lines straight across the back and well-marked pale and dark bars on the flanks.
  • Juvenile has neck not quite as dark blackish as the adult, and the dark neck blends into the paler breast color; vs the adult has a truly black neck (in shadow in the lower photo here) with very distinct edge and no blending to pale breast (but in some dark western subspecies the black neck may blend into a dark brown breast even on adults)
Similar differences in feather shape and pattern should allow ageing of other species of geese as well.


Jason Kessler said...

Fascinating. A bird ID opportunity right in front of me all the time, and I was unaware.

I'm heading over to the Hudson.

Many thanks.

Kirk said...

Good Stuff. I think people tend to ignore Canada Geese as being common or, even worse they simply call them "sky carp." They are really quite beautiful in the same way of the subtle beauty of a sparrow. Thanks for another excuse to look closer.

Toronto real estate agent said...

Quite beautiful indeed! I used to watch them all day long by the lake we had by our house when I was little. I even thought they were prettier than swans...haha. Even today, I think they have something magical about them.

Take care, Julie

Hilke Breder said...

Now I have another reason to check out Canada Geese, other than looking for a Cackling goose. Makes looking much more interesting. They are really quite beautiful birds.