I'm pretty wiped out from events today- see my post to Cobirds below.
Folks- I thought I'd recount the events surrounding today's Ross's Gull at Lagerman Reservoir, Boulder County (http://www.coloradocountybirding.com/county/bird_a_county.php?name=Boulder#362).
I got a late start of it this morning, heading out towards Boulder Reservoir a little after 9:30 to see if yesterday's wave of scoters dropped any on that water body. Since Lagerman is on the way there from my house, I pulled into the lot there to see if anything was about. Arriving around 9:40, I immediately noticed a few dozen gulls on the little spit extending from the west shore. I put my scope on them and quickly noted a small gull with a post-occular spot standing amongst the Ring-billed Gulls. Nice- a Bonaparte's, I thought. Meanwhile, my scope's optical surfaces were quickly fogging up (I had kept it in my vehicle overnight and it was still chilled), so I spent about 5 minutes trying to dry it off and warm it up in the sunlight while scanning the lake with my binoculars. Not seeing much of interest, and with my scope revived, I returned my attention to the spit, about 350 meters to the southwest by Google Earth estimate. The small gull had gotten partially hidden behind a larger ringer, but I could see its head, which was clean white except for the previously mentioned small dark spot behind its eye. The bill struck me as a bit small, but at that distance I wasn't going to worry too much about that. The bird started walking out the spit towards the lake, behind roosting Ringers, but in the gaps I could see it progress and I thought it odd that I couldn't see any dark primaries. Still, I didn't have any long, clear looks, and really didn't think too much about it yet. The bird kept going, eventually stopping at the end of the spit. I was a bit perplexed by what seemed to be a pink cast on its breast, but wrote it off to sun glare off the water. But something was seriously beginning to twitch in the back of my birding consciousness- what was up with that bird? Maybe something about the head shape and proportions didn't fit. Then it picked up and began to fly the length of the lake, making a couple of laps along the far side. Now I could see the dark gray underwing, with a pale trailing edge, and thought I must have found a Little Gull. I didn't pay super attention to the tail at the time, and the bird returned to the water near the spit, swam in, and walked back up with the Ringers to settle down again. Now I could see for sure that there wasn't any black in the primaries- they were a nice uniform silvery gray along their whole length, and they looked long, projecting well back from the tail. Was that right for Little Gull? Having very little experience with Little Gulls (N=1), I trotted back to my car to grab my Sibley Guide, and returned to my scope to compare field marks. Well, I immediately saw that Little Gull should have very short wing projection and a darker cap, neither of which this bird had. I knew it wasn't a Bonaparte's Gull from the lack of black in the primaries and the wrong underwing pattern, so what the h-e-double hockey sticks was I seeing? Now my mind was turning to the possibility of something much less expected, and I thumbed back to the Ross's Gull page, with favorable comparisons to everything I was seeing. I was trying to rule Ross's out and anything else in, and was angling to get a better position to see the bird when it took off again. Now I was very seriously tracking its flight in my scope, trying to gauge its tail which looked a little long, but otherwise gave no shape clues from the side-on view. Finally, though, the bird wheeled up and hovered for a few strokes before plopping down on the water, spreading its tail as it did so. My heart leapt into my throat when I saw the steeply graduated, spade-shaped tail. The bird kept flying around the dam area giving a few more looks at its spade-shaped tail, and I stayed on it for a few minutes until it returned to the spit. I began calling everyone I could think of, getting voice mail after voice mail until reaching Nathan Pieplow who graciously posted the bird for me. Checking my sent phone call log, I see that I began calling people just before 10 am.
As Nathan and a host of other birders were inbound, and as I was continuing to make more calls and give directions, a Northern Harrier cruised along the west shore, first making the gulls on the spit nervously wake up, pulling tucked heads from out of wings and standing up, and then they flushed out over the lake. I was just beginning to walk around to the south side of the lake to get closer to the birds and to get better light, and wasn't too worried since the gulls immediately began to return to the spit after the Harrier passed. Ending another call, I set my scope down to get new bearings on the Ross's Gull but I couldn't find it. No worries- must be out on the lake, right? Nope- couldn't find it there, either, nor did I see any small gulls flying around. I backtracked to the picnic shelter area to re-group and start searching again, and soon thereafter Nathan arrived, followed by numerous other birders, but we couldn't re-locate the bird. Groups fanned out to check nearby water bodies with no luck, and I got updates throughout the day on other lakes in Boulder & near-Boulder Weld & Larimer counties- a few Bonaparte's here & there but no Ross's. Meanwhile, there was a constant monitoring presence at Lagerman to see if the bird returned, but no such luck. I went back at sunset to find Roger Linfield & Peter Gent but only one Ring-billed Gull remained on the lake- apparently the spit is a day roost but the gulls head elsewhere to spend the night. Hopefully the Ross's Gull will follow its pattern from today and head back to Lagerman in the morning, or show up at another area lake for more birders to see.
I'm very disappointed that the bird didn't re-appear anywhere today, but I also appreciate and am grateful for the massive effort that dozens of birders put in today looking, and for the coordinated updates they provided throughout the day- I know many itineraries were abandoned to join in the search. Still, there's a Ross's in our midst somewhere, waiting for the next keen birder to take note. So keep your eyes & scopes peeled, and good luck to searchers able to look for this bird tomorrow.