[cobirds] Denver area gulls (Arapahoe Co.)

I spent much of Saturday afternoon (Jan 10) looking at gulls at South Platte Reservoir in South Platte Park, and I stopped by Aurora Reservoir late this afternoon (Jan 13).  Saturday at South Platte, gull numbers and variety were lower than reported in previous days.  Highlights were 5 Lesser Black-backed Gulls and 3 Thayer's Gulls.

Aurora Reservoir (fee area) was 99% ice covered today, but I had a bit of luck with small patches of open water being on the east side of the lake and thick clouds making viewing toward the west possible.  Gull variety was good, and viewing was good but brief as gulls arrived from the landfill, bathed, lounged for a bit, and then left.  The ongoing, beautiful adult (or third cycle?) Glaucous Gull was present, along with at least 3 Thayer's and 7 Lesser Black-backed Gulls of various ages.  One pale first-year gull appeared to be a hybrid Glaucous-winged x Herring Gull.  A somewhat darker (gray brown) first-year gull, with more uniformly colored back, tertials, and primaries, I identified as a probable Glaucous-winged Gull, with the caveat that it's hard to rule out some Herring influence in that one, too.

South Platte and Aurora each had several hundred gulls, but I think this is only a fraction of the total in the area.  And neither location seems to be the nighttime roost.  Gulls headed ENE from South Platte Reservoir Saturday at sunset, and WNW from Aurora Reservoir today at sunset.  Where are they going at the end of the day?  Cherry Creek SP?  Quincy Reservoir?  Or even Barr Lake?

David Dowell

Longmont, CO

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