[Tweeters] That Ocean Shores white goose

Bill Tweit bill.tweit at gmail.com
Tue Jan 16 21:53:59 PST 2018


There is a story here. The conclusion is that it is a Ross's Goose.
Likely an older male. The story is both cautionary and instructive, and
explains how we have a reasonably educated guess about the sex and age.

A lot of folks have gone to see that goose, called it a Ross's, and a lot
of great photos have been posted on eBird. One observer, Rachel Hudson,
had trouble convincing herself that it was a Ross's, for some very good
reasons. She thought the beak looked a bit too wedge-shaped, the feather
line seemed wrong, the head did not look as rounded as it should, and
overall the bird looked too bulky. The collected eBird photos show she was
right on all counts; it has an unusually shaped beak with a lot of
caruncles and does not have a typical head shape. As a result of her
concerns, she submitted it to eBird as a candidate for Snow X Ross's, a
fairly frequently noted hybrid, as it didn't seem to her to fit a pure
Ross's and it clearly was not a Snow.

When I read her analysis contained in her eBird checklist, I'll admit to
smacking my forehead in some exasperation at myself. I had seen the bird
just a couple of days previous, from a distance, and casually called it a
Ross's without giving thought to the hybrid possibility. I ignored a
nagging doubt I felt at the time that the bird did not look as small as it
should have in comparison to the Greater White-fronted Geese, and was
content to "slob bird" it as a Ross's. After all, I had more important
things to do like looking for more crossbills!

We, the eBird editor crew, circulated some of the better photos to others
with more white goose experience for their opinion about the possibility of
a hybrid. Meanwhile, Rachel did some digging of her own, finding an older
scientific paper titled "Winning with warts? A threat posture suggests a
function for caruncles in Ross's Geese." This paper noted that older male
Ross's develop more extensive caruncles on their beaks, which explains the
different beak shape and feather line. Males also tend to be larger than
females, explaining the bulky appearance. And, the response we got from
Steve Mlodinow, who has the opportunity to study a lot of white geese of
both species on his home turf in Colorado provided confirmation that it is
a Ross's; he also noted it was likely a male. The instructive part of the
story is that it is sometimes possible to ascertain the sex of an
individual Ross's Goose in the field, with close attention to detail.

The cautionary part of the story is that it confirms several birding
adages.

- Identify it for yourself, don't just take someone else's word for it.
- Ask questions if the identification doesn't seem to fit. This is how
we continue to improve at our craft, by close observation and keeping an
open mind.
- And, do your own research. After all, you might stumble across a
scientific paper with an even better title than "Winning with warts"!


Bill Tweit
​O​lympia, Washington
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