I wasn't specifically in Iowa for the birds last weekend, but as any other addict can attest...one manages to fit in some time all the same. Eastern Iowa isn't the birdiest of places in winter. It doesn't benefit (consistently) from the boreal winter species, the Crossbills, Redpolls, Northern Shrikes or Gallinaceous birds. It also loses most of its spring and summer residents, and this ultimately results in a fairly depauperated bird population until later March.
With the terrestrial bird scene so desolate, the Mississippi River provides one large artery--a life line, if you will--for desperate winter birders. If one is willing to brave the cold and icy wind, there are plenty of Gulls and Waterfowl, along with scores of Bald Eagles, wherever there's still some flowing water. Herring and Ring-billed Gulls make up the vast majority of the Gull population, but Thayer's, Black-backed, and Iceland are also known to mingle in these big noisy groups. When our other birding leads grew cold, the Iowa Voice and I spent time trying to pick some rare individuals out. I do not think we saw any Iceland but we got at least one mature/adult Thayer's, of which I did not get any presentable photos. The shots below feature only Ring-billed and Herring Gulls, but do show some of the multifarious plumage messes with which unfortunate birders must deal. I know that with anything larus, I am very gullible...(that's right, I went there!)
My best bet at photographing a Thayer's Gull came with this immature bird. Adult Herring and Thayer's Gulls look very similar, and the immatures do too. Since I had very little experience to draw upon with Gulls, I had to defer to my Sibley's guide. The guide shows young Thayer's having mottled markings all up the base of the tail, like this bird, but also lighter secondaries and primaries on the wings. The rump on this bird looked good for Thayer's, but that's a more variable characteristic and the wings indicated a Herring Gull, as was confirmed when I later conferred with some Gull Guys.
The immature Herring Gull below had the standard white rump shown in the Sibley's, and while I never held out hope that it was anything but a Herring, the synchronized pursuit of an opportunistic Ring-billed Gull made for an interesting encounter.
As the rookie Herring Gull tried to get away with its catch, the Ring-billed matched it wing beat for wing beat, stroke for stroke, pressuring and harrying this greenhorn Gull to drop its lunch. These birds had pretty impressive, if also antagonistic, high-speed synchronization. It would make the Russian and Chinese Olympians envious for sure, and here they were showcasing along the frigid Mississippi. This scene could definitely have used some slow-motion video and a classical music soundtrack.
Above the Mississippi River and the nearby dam there was a massive, swirling cloud of screeching Gulls. Like a large, aggressive school of fish, they'd turn and fluctuate together, riding the currents and looking for any opportunity to feed. Soon after this Herring Gulls made its catch, both it and its pursuer disappeared back into the amorphous larus mass above and, so the extent of my knowledge, were never seen nor heard from again.
So I didn't come away with any conclusive Thayer's or Iceland photos to share, but there was some excitement on the river, more in fact than I was expecting in the inclement conditions.