Late yestereday afternoon, I returned to Stearn's Lake to relocate the goose
that I identified on Sunday as a dark morph Ross's Goose. I had not considered
the possibility of a hybrid and wanted to recheck the identification. I was
primarily concerned about a possible Ross's x Snow Goose. However, as I arrived
at the Stearn's Lake parking lot, Joe Roller called to discuss a similar goose
that he had observed at Stearn's on Monday. He urged that I look closely at the
body color of the goose on the possibility that it might be a hybrid with a
Cackling Goose rather than a Snow.
There was considerably more open water on the lake yesterday (about 80%) than
on Sunday (about 30%). There seemed to be more geese also. The single white
Snow Goose was readily visible from the parking lot. I walked around the south
side of the lake, stopping first along the southwest edge. I quickly found two
dark morph Snow Geese, both on the west side of the lake. I then scanned the
farther side of the lake, and toward the dam I spotted a dark morph Chen or
Chen hybrid goose. The goose was small relative to the majority of Canadas, had
a more rounded head than the Snows and appeared to have a stubbier bill. The
observation, however, was at a good distance and the bird was in a mass of
Branta geese. I walked further along the trail to the dam and up on the dam
road. From the dam I was able to relocate the smaller Chen goose. At this
point, the bird was backlit, and the light was fading. The bird was about the
size of the Branta geese that I judged to be Cacklings. The head and neck were
white with a few brownish fleckings on the neck. There was no black on the back
of the neck or top of the head. The bill was relatively stubby and appeared to
be a pale bluish gray at the base with perhaps some pink toward the tip. There
was no suggestion of a grinning patch. The body color was brownish gray tending
perhaps a bit more gray than the Branta geese. There was no white visible on
the wings. The breast below the white of the neck was pale as in some Canadas
and Cacklings. The base of the bill was somewhat crescent shaped and seemed to
fall between the straight edge characteristic of the Ross's Goose and the
crescent of the Snow. The feathers under the tail were white. When the bird
flew along with the mass of Canadas and Cacklings around it, I thought I caught
a glimpse of white rump, but it quickly melded into the flock. Overall, my
impression was of a possible hybrid. If the Ross's do hybridize with Cackling
or small Canada Geese, it may well be a Chen/Branta hybrid. Several of the
impressions I had Tuesday were different from those I had Sunday. On Sunday,
the rounding of the head seemed more distinct than in the views I had Tuesday.
The body color seemed more blue gray Sunday and the bill more pink. On Sunday,
I was much closer to the bird and the light was better. It almost seemed they
might have been different birds, but the likelihood of two small Chen-like dark
morph geese in the same flock of Brantas seems low.
Illustrations and discussions of dark morph Ross's Geese and Ross's Goose
hybrids are sparse in the literature. Of the field guides on my shelf, only
Sibley illustrates the dark morph. The National Geographic Complete Birds of
North America has an illustration and the most complete discussion that I've
found so far of the dark morph. Only The Birds of North America Online mentions
the possibility of a Ross's x Cackling with no discussion. In addition to his
observation of the suspected Stearn's Lake hybrid Monday, Joe Roller recalls
seeing a similar bird on another Boulder area lake 6-8 years ago.Chuck
Hundertmark2546 Lake Meadow DriveLafayette, CO 80026Phone/fax:
303-604-0531Cell: [email protected]
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