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Thursday, January 25, 2007

Birding on Ice

Last Monday, I diverted myself to Boulder Creek just west of 75th street in W. Boulder. Wedged between the Boulder water treatment plant to the south, private lands to the west and south, and off-limits open space (how's that for an oxymoron) to the east, this little stretch of creek offers about 1/2 mile of great riparian birding.

The lower half of this stretch used to stay open all winter, warmed by the effluent of the water treatment plant. The birding there often was often proportional to the severity of the winter- as other stretches of the creek froze, birds would take up residence in the artificially warmed environment.

Well, it turned out that another municipal water supply intake was below the output of the treatment plant. Seems that they objected to this arrangement (can't imagine why), so a couple of years ago the outlet pipe was extended to emerge just downstream of their water supply intake. The problem is that the warm water now flows through a closed section of open space- major bummer for winter birding.

So back to the tale of my recent visit- with our 5 weeks of successive snowstorms and cold weather, the stretch of creek was mostly frozen and snow covered. As much as I missed the steaming treated water, it was cool to see the creek in its natural icy state. A few very narrow stretches of fast-moving water were still open, and sure enough, birds were taking advantage of the openings. It is really fun to see American Dippers dive right into the fast water, stay down for a while, and then whip back onto the ice shelf, kind of like mini gray penguins. They seemed to be coming up with plenty of caddis fly larvae and little snails. Some of their favorite perches were littered with the gravely remnants of the little rocky tubes the caddis larvae live in for protection. It is spooky to think about what would happen if the current carried a dipper under the ice, with no downstream openings sometimes for well over 100 yards, but they clearly know what they are doing.

As the dippers were out on the ice instead of along the bank, the best photo angles were also from the ice. At one place I chanced crossing a side channel where deer tracks preceded me, knowing that if the ice gave way I would be wet below my knees but otherwise OK (of course, my outing would then be done, too.) This got me to a mid-stream gravel bar right by an open water race being worked by a dipper that seemed to ignore me as it dived nearby. My challenge was to try and snap some pics mid-dive. Turns out that when they dive, they dive fast and without warning since they are dipping all of the time up on the ice. So after, say, 20 fake dips, suddenly they just do one more dip and plunge in. I got lots of throw-away shots (thank goodness for digital media), but a few came through in various states of mid-dive. Interesting how their body shape sleeks down when they dive- they no longer look like their normal plump selves, instead almost taking the shape of a warbler or sparrow in flight.
Common Goldeneyes also were working the narrow, fast-running gaps in the ice. Some of the gaps were so narrow that the goldeneyes barely fit, but they would be churning along on the surface like they were on a watery treadmill, catching their breath between dives. Birds that were flushed by me or by other trail users would fly up or down stream to another open stretch where they resumed their foraging.
Another open patch hosted a Great Blue Heron, and at one point a female Common Merganser came screaming in from downstream, feet down to land right in front of me on a thread of open water. It saw me at the last minute and veered back up skyward, undoubtedly indignant at my presence along its intended landing zone. It let me know what it thought of the situation by letting fly a white stream of excrement before continuing on its way upstream to another more private spot. I took no offense, though- I was enjoying the stolen hours of winter birding way too much.


Tony Morris said...

Great pictures of the American Dipper, one of my favourites families!

Snail said...

Fantastic shots of the dipper!

Patrick B. said...

Awesome shots! I tried finding dippers while visiting Colorado in August (Vail area and Rocky Mountain NP), but I struck out! These pics are the next best thing.