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Sunday, February 10, 2008

The Power of Suggestion

Denver-area winter birding spot Cherry Creek Reservoir has been hopping with good birds over the last few days, including reports of 9 species of gulls. The keys at big lakes like Cherry Creek are patience and good glass, and it also doesn't hurt to spend the hours with good birding buddies, either. Having one or more friends around helps a lot with bird spotting as one sifts thousands of Ring-billed and Herring Gulls for the goodies, and helps to pass the time during lulls (like yesterday, when nearly all of the gulls departed for a couple of hours in mid-afternoon.)

Another bird of note at Cherry Creek has been a juvenile swan. Swans can be deceptively tough to ID when you don't have up-close field guide looks at adults. The open patch of water that has been the base of operations for this bird is about 500 meters out from shore, and often the air gets quite distorted over the ice. As if that wasn't enough of a problem, young swans don't develop some of the most important field marks until they mature- things like the shape of their bill or the shape of the junction with the bill and forehead can be unpredictably out of whack on first-winter birds. Lots of indicators pointed to Tundra Swan, including black legs and a concave upper bill edge. So for a couple of days, the RBA and state list serve were reporting it as such. Yesterday, though, a competing ID theory developed with its own supporters pointing out features like the immense size, all-dark lores, and long neck as indicative of Trumpeter Swan.

I didn't arrive until about noon, and soon got onto the swan, which was standing near and completely dwarfing a Canada Goose (a large subspecies, too- not a lesser Canada Goose.) The bird stretched, craning its neck, which was amazingly long. Seeing this for myself, and with the arguments for Trumpeter fresh in my mind, I had no problem agreeing with the call- Tundra would be bigger than a Canada Goose but not that big. Throughout much of the afternoon I happily shared my scope with other birders and casual passers-by, telling them it was a young Trumpeter Swan.

How wrong I was.

So were the Tundra Swan folks right? Nope.

You see, Trumpeter and Tundra Swans are the only species on the state list, and we all fell into the trap of trying to make the bird one or the other. But while I was happily pointing out the bird to folks, Bill Maynard had gone home and was studying his digiscoped pictures to try and settle the issue. His conclusion was that the bird was a young Mute Swan, which explained the seeming contradiction of field marks. Coincidentally, just after he posted his thoughts to the state list, Mike Freiberg and I were photographing the bird as it flew over us, heading off beyond the dam for about ten minutes before thinking better of the sojourn and flying back to its hangout in the middle of the lake. I didn't look at the photos at all, though, until my dad called me to tell me about Bill Maynard's post. Mike and I grabbed our Nikons and zoomed in on the flight shots, and essentially smacked our foreheads with the realization that it indeed was a Mute Swan.

So what are some things that I take away from the experience?
• This is an example of why the birding lifestyle is cool- healthy, friendly ID debates and sometimes surprising resolutions.
• A great example of seeing what one expects to see instead of seeing what one is actually seeing.
• A reminder to keep the mind open to possibilities beyond the expected, particularly when a bird isn't quite "right."

So at this point I hand it off to the Colorado Bird Records Committee. I don't think there will be any debate about the ID, but with people around the country keeping Mute Swans in their ponds, the provenance of the bird will be debatable. On the other hand, established wild populations of this Eurasian species exist up and down the East Coast and through the Great Lakes, and perhaps in Missouri and Montana as well, so making the flight to Colorado from one of these wild populations wouldn't be too much of a stretch for such a bird. It doesn't show obvious signs of aviculture (like a band or clipped or oddly worn wing feathers), but not all waterfowl enthusiasts band their birds, I suppose. Whatever the eventual verdict, it is a very interesting bird and sure to generate much more discussion before the whole episode is over.


brucesc said...

Very interesting story and superb flight photos! To say nothing of the good lessons. I guess that means I'd better go scope very carefully the hundreds of tundra swans we watched over the weekend.

Anonymous said...

Doesn't look like a young mute swan though.....(to me)... we have a lot of them here, as well as trumpeters..but I agree to your greater widsom on all birding as I am a new birder. Lovely flight shots...with a Nikon?

Sean Fitzgerald said...

Good post Bill. Power of suggestion/expectation is truly a force to be reckoned with. Congrats on snagging the nemesis wren too!
-Sean Fitzgerald