[obol] Re: Taverner's Cackling Goose vs. Lesser Canada Goose
- From: Hendrik Herlyn <hhactitis@xxxxxxxxx>
- To: David Irons <llsdirons@xxxxxxx>
- Date: Wed, 15 Oct 2014 10:51:30 -0700
Hi Dave and all,
Thanks, Dave, for your insightful coverage of this topic. I used to spend a
lot of time (mainly at Finley NWR and the Oregon coast) trying to sort out
the various (then) subspecies of the Canada/Cackling complex, and I have to
agree with Dave, I never felt very confident about being able to separate
Lessers from Taverner's.
I fact, I was rather surprised to find out that Taverner's was assigned to
the Cackling species after the split. To me, it always appeared much more
like a small "honker" than a "cackler" (and again, I can only second what
Dave said about their voices).
It would be nice to see more studies done on those intermediate forms. In
the meantime, I'm afraid we're stuck with the current classification - my
answer to which is: in the field I count *minima*, *leucopareia*, *occidentalis
*and *moffittii*, and I blissfully ignore the rest! ;-)
Happy goosing!
Hendrik
On Wed, Oct 15, 2014 at 12:03 AM, David Irons <llsdirons@xxxxxxx> wrote:
> Greetings All,
>
> Over the past seven years or so, I have spent a considerable amount of
> time studying and photographing the smaller forms of white-cheeked
> (Canada/Cackling) geese that winter in the Pacific Flyway. While most of
> these efforts have been made within what might be referred to as the
> Willamette Trough–from Ridgefield NWR south to Eugene–I have also studied
> Aleutian Cackling Geese in Humboldt County, California and spent a fair
> amount of time looking at the birds that winter in pastures along the lower
> reaches of the Nestucca River in southern Tillamoook County.
>
> Earlier in the day Bob Archer, Scott Carpenter and others have offered
> some good tips for separating the two predominant forms of Cackling Goose
> in the Pacific Flyway. Ridgway's Cackling Goose (subspecies *minima*) now
> winters mostly in the Willamette Valley and extreme southwest Washington.
> Aleutian Cackling Goose (subspecies *leucopareia*) is for the most part
> a coastal migrant in Oregon and northwestern California and then turns
> inland to winter in California's Central Valley.
>
> You will be hard-pressed to find any source that offers meaningful
> criteria for separating the third Pacific Flyway form of Cackling Goose
> (*Branta
> hutchinsii taverneri*) from Lesser Canada Goose (*Branta canadensis
> parvipes*). In fact, most descriptions of these two taxa compare them to
> one another and describe them as being the same size and virtually
> identical in appearance. In the ID pdf shared earlier today by Bob Archer,
> the culmen measurements offered for both forms (32-40mm) are identical.
> I've photographed birds that I initially presumed to be Lessers and other
> birds that I initially presumed to be Taverner's Cacklers and compared lots
> of birds in the field. I've never been able settle on any differences other
> than those that fall within a cline that I think can be attributed to
> individual variation. Based on what I've seen, the range of variation in
> the "Tav/Lesser" grouping mentioned by Scott Carpenter is certainly no more
> extensive than the variation that I see among *minima* Cacklers. I find
> it particularly telling that an otherwise accurate and authoritative
> treatment of the ID criteria for white-cheeked geese (the pdf shared by
> Bob) includes not a single comparative of image of Lesser v. Taverner's,
> even though both forms supposedly winter side-by-side in the Willamette
> Trough.
>
> In my opinion, the voice of the putative subspecies Taverner's is honking
> and more Canada Goose-like and not at all similar to the higher-pitched
> yelping vocalizations of other subspecies of Cackling Goose. This, along
> size differences between Taverner's and the three other Cackling Goose
> subspecies, suggest to me that what we know as Taverner's Cackling Goose
> may be more closely related to the Canada Goose group. Taverner's are
> significantly larger than the the three other forms of Cacklers and they
> are close in size to Lesser Canada Goose and Dusky Canada Goose. Given that
> Taverner's and Lesser breed and winter in the same areas, look alike and
> sound alike, what criteria should we use to sort them? I recall reading
> somewhere that a mtDNA study showed them to be distinct subspecies, but I
> haven't the foggiest notion of how one might separate them in the field.
>
> As Scott mentioned, even after much study there are birds that can't be
> safely assigned to subspecies. I routinely see "tweeners" that I can't
> confidently slot to subspecies. That said, I think that the majority of
> Ridgway's, Aleutian, and Richardson's Cackling Geese can be identified in
> the field. However, separating Lessers and Taverner's in the field remains
> a challenge even for the most experienced goose observers. I certainly
> can't claim to be able to ID them visually.
>
> Dave Irons
> Portland, OR
>
--
__________________________
Hendrik G. Herlyn
Corvallis, OR
*"Nature is not a place to visit. It is home." -- Gary Snyder*
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