Northern Maine has been hosting an exceptional number of Cackling Geese this year. Though its difficult to figure out exactly how many its pretty clear now that there are/have been at least 10 that have been seen in the area this fall.
Cackling Geese were split from Canada Geese back in 2005 and since that time, birders have been paying them a bit more attention. These small geese are most common in the western and central portions of the country with rare-but-regular appearances on the east coast. The Cacklers, as all experienced waterfowl oglers know, look a lot like small Canada Geese and the differences between the two species are subtle.
In my limited experience (as an Eastern birder) the geographically closest and most expected form/subspecies of Cackling Goose, the "Richardson's" Cackling Goose can be the most difficult to separate from a flock of Canada Geese. In general, the little geese are substantially shorter necked and stubby-billed, they have a very steep forehead and a blocky head shape. Less than half of the Richardson's Cackling Geese I've seen show a white band/ring at the base of the black neck "sock".
In addition to their very small size (in proportion to other expected forms of Canada Geese in this area), I think most of these little geese show a silvery tone to the back and wing plumage. This seems like a subtle distinction, but it can be quite pronounced and many Cacklers I see are clearly a shade lighter and more grayish than the surrounding Canadas. Differing lighting conditions can effect this, but I think I can often distinguish a Cackling Goose in closer flocks with the naked eye. Cacklers have a high pitched vocalization which is really more of a yelp than a honk. ...I think it sounds like a very small dog bark...a squeaky yap.
Like Canada Geese there is plenty of variability in appearance in the Cackling Geese I've seen here. There are some individuals that are much more easily distinguished than others. A few I just leave unidentified.
By looking solely for small sized geese, a birder can get in trouble. I believe Northern Maine has three (and maybe four) subspecies of Canada Geese visiting during migration and these vary quite widely in size. The "Giant" Canada Goose is the locally nesting form and are substantially bigger than the equally common "Atlantic" Canada Goose that breeds in eastern Canada/ Labrador and migrates through in spring and fall. Northern Maine also sees plenty of the slightly smaller "Interior" subspecies which comes from northern areas around Hudson Bay. I have seen many times where an "obviously" smaller goose and Cackling Goose candidate turns out to be an apparent "Interior" form surrounded by "Giant" Canada Geese.
There is also a very small, dark-plumaged form of Canada Goose that shows up in small numbers in Aroostook County during migration. I'm not sure what subspecies these are or where they are from, but I'm fairly confident they are not just small or young individuals of the other more common Canada Goose subspecies. I have thought they may be a dark form of the "Lesser" Canada Goose but I have yet to find any literature that says such a form exists! What ever they are, on the subspecific level, they are certainly small enough to attract attention of a birder looking for a Cackling Goose.
I thought a few photos of the Cacklers we've seen up this way this fall:
My first find this year was a sleepy little Cackler found with a flock of Canada Geese in the downtown impoundment of Limestone Stream in Limestone on 30 September 2011. Though my photo is no work of art, you can distinguish the stubby bill, steep forehead and silvery plumage in comparison to the larger Canada Goose just behind it.
I cropped another shot of this bird to better show the blocky head profile. The bill is short, the forehead is almost a step up rather than smooth. The crown is pretty flat.
Lastly I've included a shot of a Cackling Goose flock found at Collins Pond in Caribou on 19 October 2011. The Cacklers are behind the front four Canada Geese in a line through the middle of the frame. I am sure there are at least 5 short necked Cackling Geese here. There are two other small geese which show stubby bills but slightly longer necks that I also think may be Cacklers that are just showing a more alert profile than the other members of the flock. So there may be seven! Meanwhile on the other end of pond....