Saturday, October 24, 2009

Small Canada Geese in Maine

I've been using this rainy Saturday to catch up on correspondence and bird reports from the past couple weeks. As usual, I've been quite interested in all the recent goose sightings from around the state.

So far this fall we've found Canada, Snow, Greater White-fronted, Cackling and Pink-footed Geese here in Maine. (...Any Brant?) I also noticed quite a few reports this fall of smaller Canada Geese that astute birders are noticing amongst the larger individuals. I'm sure these get attention as we all sift through the flocks in search of a rare Cackler.

Though there have been quite a few reports of "Lesser" Canada Geese lately, I wanted to mention that this subspecies has yet to be definitively documented in Maine....This is not to say people aren't seeing groups of small Canada Geese in Maine just that these are probably not the true "Lesser" Canada Geese. (I know discussions of subspecies is often seen as the threshold to the realm of true bird nerd-dom but I still think there's a bit of confusion that bears clearing up.)

Size Variation: Real and apparent

In my experience, we currently see a wide variety of sizes of Canada Geese (Branta canadensis) in Maine. I think birders need to consider several things when evaluating the size of a goose and before assigning it to any one subspecies.

First is just the variation in body size of populations within any subspecies. Generally the birds in the northern reaches of the range tend to be smaller than those in the south. So larger and smaller birds within a migrating flock could be both from the same subspecies.

Sex, age, molt and diet can all work in various combinations to produce some real size extremes. Males are generally slightly larger than females and young birds are smaller than adults. Thanks to good food availability in some locales there are certainly some big, beefy geese out there and likewise there are some smaller birds that have struggled and end up true runts. These outliers usually are usually encountered in ones or twos (as opposed to whole percentages of flocks with differing sizes as is the case when subspecific size difference is in play).

Body posture, lighting, plumage erection and variation in the surface a bird is standing on can all also create some perceived differences in size. A relaxed or dozing bird can look a lot smaller than an alert or alarmed one. Likewise I've been fooled by geese that appeared small in a field, until they stepped out of a furrow and up beside a goose that seemed much larger moments earlier... A swimming bird that is angled slightly away can also look amazingly smaller than a similarly sized individual offering a true side profile. (This can also make bills seem stubby and Cackling-esque!)

Its also worth noting that some telephoto and digiscoped images have distorted perspectives that make birds further away from the camera appear disproportionately larger than those that are closer. (Ever notice how huge the batter and catcher look compared to the pitcher when the video camera in center field is being used during baseball games?)

Subspecies of Canada Geese in Maine

I'm quite confident that there are probably three subspecies that show up in numbers in Maine in the fall. I believe our locally breeding geese come mostly from the introduced "Giant" Canada Goose (B.c. maxima). As the name suggests, these are big geese. We also have another subspecies that breeds northeast of Maine known as the "Atlantic" Canada Goose (B.c. canadensis) that we see in migration. These are slightly smaller than the local birds but still quite large on average. Additionally there is a smaller subspecies called the "Interior" or "Hudson Bay" Canada Goose which generally breeds north and northwest of us (western Quebec and northern Ontario). The marked Canada Geese from Greenland, that I and others around New England have been finding, also seem to be from this subspecies rather than the geographically closer (to Greenland) "Atlantic" subspecies. Many flocks I see in October, here in northern Maine, are a fun mix of these subspecies and when these different varieties are found together the size differences can seem quite pronounced.

Lesser Canada Geese

As recognized by the current taxonomy, the true "Lesser" Canada Geese (B.c. parvipes) are breeders in the northwest parts of Canada and in Alaska and generally winter in the southwestern US. Though there probably have been a few found in the east, these are quite rare. I am not aware of any known Lesser Canada Goose, banded on the breeding grounds, that has turned up in the northeastern US or maritime Canada. Maybe someone can tell me otherwise!

Anyway, I wanted to offer this up to the inquiring minds of the blogosphere: lesser (small "l") Canada Geese in Maine are probably not Lesser (large"L") Canadas!

David Sibley has a great map on his website that shows, generally, the distribution of the various subspecies of Canada (and Cackling) Geese in North America. Its worth checking out:


1 comment:

Robin Robinson said...

Great goose shots, really captures the feeling of amazing abundance of them