Sorry that I've contributed so little of late.
Yesterday, Sean Walters and I visited Aurora Reservoir for the last 4 hours of daylight.
It was a stunning, frustrating, rewarding experience all wrapped in one
And a bit chilly
The southern half of the reservoir is frozen, so most birds are reasonably close to the dam on the north side -- if you have a scope. Be sure to pay the entrance fee if you don't have a year pass, as enforcement has been vigorous (if also pleasant) this winter.
Anyway, Sean and I arrived to 300 or so Herring Gulls, far more RB Gulls, and a variety of other gulls salted in. There were 20K plus geese on the reservoir, 90% or more Cackling. We'd only done a modest job of scanning the gulls when Cheryl Teuton and Dan Brooks pointed out the Black Brant sitting nicely at the nw. corner of the reservoir. As we headed in its direction, a Bald Eagle came by, and pretty much every gull left the reservoir (excepting some Ring-billeds). Rather stunning actually. A lot of the geese fled, too. Over the next couple hours, most of the large gulls returned, and the geese returned with reinforcements.
During the last hour, birds poured in. A single flock of incoming gulls contained 3100 birds, all of which appeared to be Ringers. Goose flocks came by very 5 minutes or so, numbering 500 to 5000.
In the end, among the gulls, we were able to detect
2 first year Glaucous-winged Gulls
2 Glaucous-winged x Herring Gulls
14 Thayer's Gulls (this is really an estimate, and given how hard they are to pick out, the number was probably larger)
18 Lesser Black-backed Gulls (mostly adults)
The ongoing first-cycle Great Black-backed Gull (towering over the lesser gulls)
2 immature Glaucous Gulls
and one utterly baffling Thayer's/Iceland thing
For waterfowl, the duck of the day was the ongoing female White-winged Scoter.
Our final estimate of Cackling Geese was a staggering 115,000 -- but only 1000 or so Canadas.
The Black Brant was a delight. As far as I can tell, this is the same bird that has been seen over the last month or so in Adams County and at Aurora Reservoir -- all pics show a first-year bird similar in color.
In part because we were distracted by so much activity, we picked out only 3 hybrid geese, one each of Snow x Cackling, Ross's x Cackling, and G White-fronted x Cackling (compared with 9 hybrids in a flock of approx 37.5k geese in the Poudre Ponds on north side of Greeley on same day).
Turnover here is significant, and one should not assume that today's gulls are the same as yesterday's. At one point, the Glaucous Gulls being seen here were adults. Now, immature. The first Iceland Gulls were adults, the ones seen later youngsters. The ratio of LBB Gulls seemed distinctly more skewed towards adults today than last week.... and so on.
So, goose hybrid musings.
It seems to me that, in n. CO, white-cheeked geese - particularly Cacklings - become more common as one goes from Sedgwick County to Weld (and into Boulder/Larimer). On the other hand, Snow and Ross's Geese show the opposite pattern. Hybrids often look rather like the blue form of Snow Goose (see https://www.flickr.com/photos/36088296@N08/albums/72157640339259034), and I think that for every "real" Snow Goose that I see in Weld/Boulder/Larimer Counties I see 2-3 of these hybrids.
For some reason, the Snow/Ross's x Canada/Cackling hybrids seem to prefer to hang out with Cackling/Canadas rather than Snow/Ross's flocks. In Europe, Graylag x Canada hybrids behave similarly, usually hanging out with Canadas. Dunno why.
So
On that note
Good Luck and Good Birding
Steven Mlodinow
Longmont CO
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