Please click on image to ENLARGE closeup of a Canada goose in Northwest Arkansas. I didn't have a handy photo of a white goose to illustrate Joe's essay, but I hope everyone enjoys seeing this friendly Canada a few feet from World Peace Wetland Prairie.
Here in the western Ozarks we don't see many geese at mid-winter, but
the skies should be full of geese heading north anytime now. Got me to
thinking about two geese at Lake Atalanta in Rogers ? a white Snow
Goose and a white Ross's Goose. These birds are easily seen and easily
photographed and all of us who enjoy birding there have seen them many
times. But who are they, exactly?
I photographed them up close and personal by accident on December 5,
2010. In one image you can see their bills, legs, etc. With the images
up on my computer at home, what strikes me is their similar size and
shape. Compared to Ross's in the same image, Snow Goose has the
obvious grin patch, heavier/larger bill. The legs of the Snow Goose
are thicker. I am puzzled by how close they are in size, but didn't
get any further with it until Doug James and Elizabeth were up there
recently and Doug noticed the exact same thing: if you are close
enough to see the grin patch, you can separate them by that widely
accepted field mark, but the size is so close that no real difference
Species accounts in the Birds of North America (BNA) series help
expand the mystery. To begin, these geese have a close genetic
relationship. That is, they are basically sisters. Snow Geese that
winter in Arkansas are mainly assignable to the subspecies called
Lesser Snow Goose. There is additional geographic variation in body
size and other characteristics related to growth conditions during the
prefledging period in the Arctic. For example, one study cited in BNA
demonstrated that early-hatched goslings had access to more food and
presumably better growth opportunities. So what happens on the ground
in the Arctic must influence the size of birds we see in Arkansas.
In terms of Ross's Goose, they are rarely found with the form called
Greater Snow Goose, but often with Lesser Snow Goose. DNA analysis
shows that Ross's is a sister species with Lesser Snow Goose. So the
sisters migrate into Arkansas and maybe that is who is at Lake Atalanta.
My conclusion in all of this is that apparent size similarity may be
reconciled as follows:
1. The Snow Goose at Lake Atalanta is the form Lesser Snow Goose
2. This Lesser Snow Goose may be even smaller than other Lessers
because of various ecological conditions in its prefleging growth
3. Male Snow s are modestly larger than females, so our Snow may be a female
4. Male Ross's are heavier than females in winter, so our Lake
Atalanta bird may be a male
By juggling all of this stuff, it is possible to logically squeeze
these two real live wild birds at Lake Atalanta into the same size
frame: a small female Lesser Snow Goose and a large male Ross's Goose.
Like we used to say in the Forest Service when confronted by the
unexplainable, That's my story and I'm sticking with it.
JOSEPH C. NEAL in Fayetteville, Arkansas