This has been the scene over many of our inland reservoirs of late, although the mobs of gulls have begun to dissipate. One of the best places for gull fanatics was Hoover Reservoir in central Ohio, which at its peak may have had 20-30,000 birds. As would be expected, most were Ring-billed Gulls, with much lesser numbers of Herring Gulls. Of major interest to birders were unprecedented numbers and variety of rarities: Lesser Black-backed, Great Black-backed, Glaucous, Iceland, Thayer's gulls, and even a Black-legged Kittiwake. All of these species appeared on land-locked reservoirs, and all are rarely found away from Lake Erie waters in Ohio.
The numbers and variety were unprecedented, and they hung around for a week or so. At times, the gull-laden lakes resembled East 72nd Street in Cleveland (above), where you'd expect this sort of action. Why?
The answer probably is piscine in nature. Gulls love gizzard shad. If you are a chocoloholic, you may fantasize about being dropped into a giant jar of M & M's. If you are a gull, the above is your fantasy world. Waters packed with dead and dying shad. Events like the above are a regular occurrence on Lake Erie, but less common inland.
However, after a talk with Scott Hale, a Division of Wildlife fish guru, I learned that inland shad populations had a very late hatch last spring. Thus, when last winter's cold and nasty weather arrived, the young shad were less able to survive the extended ice and snow cover that blanketed many lakes, and big die-offs resulted. Which resulted in an absolute bonanza of food for gulls in places where there normally aren't such opportunities.
Gizzard shad, Dorosoma cepedianum. They are common to abundant in many of our lakes, but not especially tolerant of long cold snaps that result in long-term ice and snow cover.
Although various theories have been out about how and why all of these gulls found the inland lakes and the fishy food source, my hunch is that most of the birds dropped down off Lake Erie and the other Great Lakes. Highly mobile omnivores such as gulls are incredibly adept at locating new food sources, and possibly somehow the locations of new opportunities get communicated.
Whatever the reason, show they did, and we got some amazing records of gulls as a result.