recent gull watching at Aurora Reservoir (Arapahoe County)

[David Dowell]

We've heard much about the gull and goose magnet that is Aurora Reservoir this winter, and I'm providing a more recent update.  I've been there during afternoons once or twice a week during the past month to practice observing gulls.  (Last year, it was Teller Lake #5 in Boulder County, this year it's Aurora Reservoir in Arapahoe County.)  Many of the gulls there look quite familiar now.

During the past month, gull watching has been good any time during the afternoon.  (I haven't been during the morning so don't know what it's like then.)  As reported previously, gulls come and go during the afternoon, typically passing over the curved part of the dam on the north side of the lake, going to and from the landfill.  Some of the better viewing has been in the early to mid afternoon, when the gulls calmly assemble in groups that are good for viewing.  Late in the afternoon, the gulls are frantic, but that's when the big numbers are there, and often I see gulls then that I didn't see earlier.  Each time I've lingered until sunset, the gulls have suddenly shifted to a different part of the lake and piled into a heap that makes identification of individual birds impossible except for gulls along the edges.

The more I look at gulls, the more I appreciate the variability within each species (size, appearance, etc.).  A point of recent frustration has been how hard it is to judge leg color.  I don't understand how legs can appear pink from one angle and yellow from another.

The lake fared well during the last cold snap, keeping some open water and good ice shelves for the gulls.  I'll be interested to hear any reports of whether the lake manages to get through the upcoming cold snap without icing over completely.  Fog has been a problem when the air temperature has been about 20 Fahrenheit or less and/or when the humidity has been high.  Otherwise, viewing has been good -- from the marina in early January and from the dam more recently.  Once or twice, gulls have accumulated on more southern ice shelves, far from parking lots, when a bicycle would have been handy for getting around the lake.

Some recent gull highlights have included:

* adult ICELAND GULL on January 29

* 2 immature GLAUCOUS GULLS which really seem to like the place, observed as recently as yesterday (February 2)

* an apparent first winter GLAUCOUS-WINGED x HERRING hybrid on January 29, perhaps seen previously during the past month or two

* LESSER BLACK-BACKED GULLS, 2 yesterday (February 2) but as many as 4 on February 1 (2 adults, 1 juvenile, 1 2nd/3rd winter)

* THAYER'S GULLS, at least 4 yesterday (February 2), adults challenging to pick out as always, juveniles including one very pale one

* at least one adult California Gull (February 1) already showing breeding type plumage

* still dozens of Herring Gulls

* still thousands of Ring-Billed Gulls

I haven't had any luck with the Slaty-Backed Gull during the past month but congratulate those who have seen it.  There is also what appears to be a first year GREAT BLACK-BACKED GULL visiting the lake now and then, but I haven't had a good enough view to say for sure.  There are certainly other goodies that I've missed.

The geese have been interesting, too -- mostly Cackling, but also Canada, a few Snow, the occasional Ross's, and a hybrid or two.  Geese are sometimes there during the day, sometimes not, but they always seem to arrive in force around sunset.

A day pass for Aurora Reservoir is $10.

David Dowell

Longmont, CO

[David Dowell]

I made another quick stop at Aurora Reservoir late this afternoon, finding the lake mostly frozen.  The largest patch of open water, not all that large, was on the southwest side.  Closest access was from the marina, but a bit of a hike was required to get close to it.  This patch of open water attracted about 1000 gulls and small numbers of geese and ducks.

Hybrids were the most noteworthy birds.  A SNOW x CANADA GOOSE was there when I arrived, and then the GLAUCOUS-WINGED x HERRING GULL that has been reported previously showed up.  But the highlight was the return of what we believe to be a LAUGHING x RING-BILLED GULL.  I have not seen it there since Steve Mlodinow spotted it on November 24.  It is slightly darker than the Ring-Billed Gulls with a mottled hood, eye arcs, and a mottled bill that is more dark than light.  I am yet to get a good photo but got a low-quality one today:

http://www.flickr.com/photos/76753483@N08/12375848183/

Other birds of interest included 3 immature GLAUCOUS GULLS and 2 LESSER BLACK-BACKED GULLS (y1 and y2/y3).  No dark-mantled gulls were present, but I did not stay long and did not wait to see if there was an evening influx of gulls.

David Dowell

Longmont, CO