I.D. problem: hybrid white geese?
A photographic review
text © Don Roberson
photos copyrighted by photographer(s) credited
Here's the problem. Say you are walking by Crespi Pond at Pt. Pinos on a crisp winter's day, and you suddenly notice there is a white goose grazing with the ubiquitous American Coots on the 17th green of the Pacific Grove golf course. It's an all-white goose with black primaries: an adult. It is obviously either a Snow Goose or a Ross's Goose, both about equally rare in Monterey County and both of which have occurred multiple times in previous winters on Crespi Pond. The goose doesn't look all that big, and the bill doesn't look all that long, but it does have a black "grin patch" that is characteristic of Snow Goose.

Is it a Snow Goose? Maybe. But it does look small and details of the bill seem odd. And hybridization between Snow and Ross's Goose is known (Ryder 1969, Trauger et al. 1971). Could it be a hybrid? Maybe. In fact, I published a paper on this problem focusing on yet another goose on Crespi back in December 1990 (Roberson 1993; more on that below).

This is exactly the situation my wife Rita Carratello and I faced on 4 Dec 2004. I've gone back to study and photograph it since (on 6 & 7 Dec; photos right and below) and can firmly state: I don't know, but I strongly suspect this goose has hybrid origin. Let's see what you think.

A completely typical first-year Ross's Goose wintered at this exact same spot from 18 Dec 2002-12 Mar 2003. Here's an overview photo of it (below left) grazing with coots on the 17th green. Next to it (below right) is a photo from 7 Dec 2004 of the mystery goose grazing on the same green (but showing Crespi in the background, rather than the ocean). I use the coots for comparison because there were no other geese around to use for comparative purposes.

In comparing the two photos, it does look to me like the 2004 bird (above right) is slightly larger than the 2002 bird (above left), but not dramatically so. And, at a distance, the 2004 bird sure seemed to have a short bill. Indeed, compare it with the bill length of the 2002 bird (directly to the right) and notice that both look fairly short. I would have expected a Snow Goose to look longer-billed, even a distance.
Next, let's compare a bunch of heads and bills at closer range. Below are six shots: the top row is all of Snow Geese from different locales and at different ages. Then below them are, left to right, a Ross's Goose, the mystery 2004 goose, and the apparent 1990 Crespi hybrid.
Here's some observations about the above set of photos. Beyond some overall comments, I'll refer to two distinct parts of the bill shown on the photo (right): (1) the "bill process," an extension of the bill back toward the eye from the upper mandible, and (2) the shape of how the feathers of the face meet the bill below the "bill process":
  • All the Snow Geese (top row) have huge, honking bills. They are not only long but they are hefty. They are triangular in shape, with the thickness of the bill, measured from the top of the bill to the bottom of the bill where the bill meets the face, being at least half the length of the bill. On all the bills in the second row, the length of the bill is more than twice the thickness.
  • The Snow Geese have culmens that bulge outward slightly or that are straight (that of the young bird, upper left, bulges outward quite a lot) while the geese in the second row have slight concave culmens (middle mystery bird), or are a bit concave near the tip (Ross's Goose) or look straight (the 1990 probable hybrid).
  • Compared to the size of the head, all the Snow Geese have long bills (e.g., almost as long as it is from the bill base to the nape, if the bill were taken off and pointed backwards) while all the geese in the lower row have short bills, decidedly less than the length of the head.
  • While the mystery goose (bottom center) and the 1990 hybrid (bottom right) do have grin patches, perhaps they are not as overwhelmingly prominent as on the Snow Geese.
  • The "bill process" of Snow Goose tends to be broad, and extends well back towards the eye. In contrast, Ross's Goose (lower left) has a very short "bill process." The two potential hybrids are intermediate in this character.
  • On Ross's Goose, the bill meets the feathers of the face is almost a straight line. On Snow Goose, the feathers of the face meet the bill in curving arc: those facial feathers are convexly rounded against the base of the upper mandible below the "bill process." Again, the two potential hybrids are somewhat intermediate.
Here's a close-up of the mystery goose on 7 Dec 2004. I see:
  • prominent grin patch but a short bill
  • a concave culmen
  • a short bill process
  • a rather straight line where the bill meets the face, and
  • maybe a hint of warty-like roughness at the base of bill (a Ross's character).
All these points seem "intermediate" between Snow and Ross's, and suggest some hybridization or introgression to me.
For the record, here is a shot (published in Roberson 1993) of the probable hybrid Snow X Ross's Goose at Crespi Pond on 2 Dec 1990. It was a first-year bird with duskiness on the nape, crown, neck, and back, but in a pattern more like Ross's than like Snow. Also, in line with a photo discussion of potential hybrids shown on Kevin McGowan's web site, it looked more like a Ross's Goose with a slightly long bill and a smallish grin patch. The current "mystery goose" on Crespi, which more closely resembles a Snow Goose, is more like a potential hybrid photographed in Mar 1989 in Ohio by Mary Gustafson, and published in Roberson (1993).

With both the 1990 Crespi goose, and the current 2004 Crespi goose, we cannot prove what they are. My suggestion that they represent a hybrid of introgressant goose is a theory, which you may find to be supported or not supported by the photographic evidence.

Finally, one more "for the record" photo. In November 1984, Crespi Pond was host to both a Ross's Goose and a Snow Goose. This is the only time that they have occurred together at this site. Robert F. Tintle took this photo (below):

Literature cited:

PHOTOS: All photos © Don Roberson, except when attributed to another photographer, and then copyright to that photographer, used with permission.
Photo credits for the group of six heads: Top row (all Snow Geese): immature at Crespi Pond 16 Jan 1994 © R.F. Tintle, adult at Crespi Pond in Dec 1982 © D. Roberson, adult at Salton Sea NWR, Imperial Co., CA, 23 Nov 1973 © J. Van Remsen, Jr. Bottom row: Ross's adult at Locke-Paddon Pond, Marina, 6 Mar 2004 © D. Roberson, apparent hybrid at Crespi Pond 7 Dec 2004 © D. Roberson, apparent hybrid at Crespi Pond 2 Dec 1990 © D. Roberson.

Use the following links to other portions of the MTY checklist:

Part 1: Waterfowl through Grebes
Part 2: Albatrosses through Frigatebirds
Part 3: Herons through Cranes
Part 4: Plovers through Sandpipers
Part 5: Jaegers through Alcids
Part 6: Doves through Woodpeckers
Part 7: Flycatchers through Larks
Part 8: Swallows through Pipits
Part 9: Waxwings through Warblers
Part 10: Tanagers through Sparrows
Part 11: Grosbeaks through Finches
or just the plain Checklist (no annotations)
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Page created 7 Dec 2004