North Coast Diaries

Goose chase

The American Ornithological Union (AOU) finally decided to split Canada Goose. The big ones will continue to be called Canada Geese and the small ones will be called Cackling Geese (at least for now). Taxonomists do their lumping and splitting to reflect the most recent consensus on relationships, evolution and ecology for given species. They do not necessarily care if they've added or subtracted ticks from a birder's lifelist. They do not necessarily care if they've created a field-recognizable unit. And I don't expect them to.

But there are one or two birders out there who believe that if the AOU calls it a species then there's got to be some suite of characters that can be used to reliably diagnose every bird encountered. We've been through this with Emidonax flycatchers and large pink-footed gulls already.

I've been spending a lot of time with geese in the last couple weeks. The very large ones are very easy to tell from the very small ones. But I'm afraid that many of the ones in the middle may be undiagnosable, especially at the parvipes/tavernerii cusp where parvipes (Lesser Canada Goose) has been placed with the big form and tavernerii (Taverner's Goose) has been placed with the small form. You'd be able to sort them on their respective breeding grounds, but they may be pretty much "Canada Goose Complex" anywhere else.

I have a feeling that this "differences only matter when breeding" thing is a fairly common and under appreciated reality among closely related migrant species, especially those that are obliged to share wintering grounds. Seems like there might even be some selective benefit. The fact that we can't tell them apart away from the breeding grounds may be part of the point.

Now here's where I risk exposing my elitist tendencies....
If there is a suite of characters that can diagnose a statistically significant portion of these middle ground individuals, they are likely to be subtle. Joe-average Birder is not likely to spend enough time in the field internalizing these features to really use them. Yet, he will read about these miracle fieldmarks in Birding magazine, then go out and start naming geese. He will make what amount to guesses based mostly on what his needs are for the day list or the year list or the county list or whatever, see what he wants to see and cite some reasonably well known author as the source of his expertise.

So What?

If indeed the only point to birding is to generate lists of things to be compared annually with the lists generated by others, then it really doesn't matter.

On the other hand, maybe admitting that we can't aways make identifications to species celebrates a greater observation about nature and any prentense of greater knowledge misses the real point...

Some references:
PDF of ODFW's Guide
Sibley's Goose Guide
Angus Wilson's breakdown Posted by mbalame at December 13, 2004 7:32 PM