Wednesday, December 2, 2015

Red-breasted Merganser swarms on Lake Erie

Now that's a lot of birds! The waters at the interface of Lake Erie and the Huron River are darkened by thousands of Red-breasted Mergansers. Scores of gulls wheel overhead. Everyone is fish-seeking. Lake Erie is the most biologically rich of the five Great Lakes, and scenes like this bear out the aquatic bounty of Ohio's watery northern boundary.

A squadron of nine Red-breasted Mergansers rockets by the end of the Huron Municipal Pier. I spent much of the day here on November 22, and was once again blown away by the huge numbers of birds in the area. I've been to Huron in late fall and early winter scores of times over the years and know what to expect on a busy day, but never fail to be impressed. I wrote about some other observations from this trip RIGHT HERE. In that post, I focused on the numerous rare bird sightings that the trip produced. Here, I wish to focus on the hyper-abundant mergansers.

A mixture of molting males and female Red-breasted Mergansers bunch together over a favorite fishery. The mouth of the Huron River has long been a major migratory hotspot for this species. Huge, and I mean massive, numbers of mergansers occur in central Lake Erie, especially between the islands just west of here and the Cleveland area to the east.

Rare would be the morsel that slides down a Red-breasted Merganser's gullet that is NOT a fish. These birds are piscivorous in the extreme. A sharply serrated bill helps seize and hold the slippery wriggling prey until the bird can manipulate the morsel so it goes down the hatch headfirst.

Note this male's wispy punk rock crest. This photo is from last February at a central Ohio reservoir. By then, the males have completely molted into resplendent breeding finery.

If I were a small fish, say a shiner or shad, the last place I'd want to be is in the water under these birds. As soon as these mergansers settle on the water, they will begin diving for fish and they're very adept at catching them. The aforementioned fish species are the primary prey items in Lake Erie.

One would think that a species as abundant and glaringly obvious as is the Red-breasted Merganser would be well-studied and thoroughly understood. However, "Overall, the Red-breasted Merganser remains one of the least understood species of waterfowl in North America." That quote comes from the comprehensive Birds of North America monograph of the species (Craik, Shawn, John Pearce and Rodger D. Titman. 2015. Red-breasted Merganser (Mergus serrator), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online:

Scores of mergansers scuttle across the water whipping up whitecaps. On some unseen cue, hundreds or thousands of birds will suddenly swim-fly hundreds of feet to a new feeding locale. They undoubtedly are chasing the movements of large fish schools that they're feeding upon. This photograph shows but a sliver of a feeding flock that might have numbered 10,000 birds.

One of the few detailed studies of Red-breasted Merganser food sources was conducted in western Lake Erie. The results were published in 2008 (Bur, M. T., M. A. Stapanian, G. Bernhardt, and M. W. Turner. 2008. Fall diets of Red-breasted Merganser (Mergus serrator) and Walleye (Sander vitreus) in Sandusky Bay and adjacent waters of western Lake Erie. American Midland Naturalist 159(1):147-161). This study showed that the mergansers primarily feed upon emerald shiners, gizzard shad, and the invasive nonnative round goby - this trio of fishes forms about 96% of their diet. Such knowledge should set fisherman at ease. The huge swarms of fish-eating ducks are NOT competing for prized walleye and yellow perch.

The numbers of mergansers on this part of Lake Erie can be stupefying at times. Estimates of 20,000 birds passing by one spot in an hour have been made, as have one-day tallies of up to 250,000 birds. Such numbers would be remarkable indeed, considering the total breeding population of Red-breasted Mergansers in Canada and Alaska is thought to be about 250,000 birds. It must be noted that the margin of error for shorebound observers attempting to estimate merganser numbers is large. There is just no way to know if one is recounting birds that are swirling about in circular patterns or regularly passing by the same locale over and again. However, having seen this phenomenon on numerous occasions from low-flying aircraft while conducting waterbird surveys, I can agree that the above estimates may not be far off the mark. Any way one slices it, there are many tens of thousands of mergansers staging on Lake Erie in late November and early December.

It's smack in the middle of this migratory spectacle - likely the WORLD'S most important staging area for Red-breasted Mergansers - that a corporation known as LEEDCO wants to place massive wind turbines. These, I believe, would be the first turbines located in the lake itself. Keep in mind that it isn't just mergansers that heavily use this part of Lake Erie. So do tens of thousands of Bonaparte's Gulls, huge numbers of Common Loons and Horned Grebes, blizzards of other waterfowl species, and scores of  other waterbirds. Turbines placed in bird-rich sites can cause great carnage, disrupt migratory patterns, and cause abandonment of habitat. The Black Swamp Bird Observatory has a nice summary on wind power projects in Ohio, including LEEDCO's "Icebreaker Project", RIGHT HERE.

Courtesy of The Birds of North America Online, here is a map depicting the range of the Red-breasted Merganser. The breeding range is generally well to the north of Ohio. Our Lake Erie birds are all migrants, presumably from North America. But this duck also breeds extensively throughout northern latitudes of Russia, Scandinavia, Eurasia and elsewhere. No one has attempted to document the origins of the hordes of birds on Lake Erie. Which would not be easy.

ASIDE: I regularly share maps from Birds of North America Online (BNA) monographs, and harvest lots of useful information from these accounts. I've long had a subscription to BNA, and it is a wealth of information about birds. BNA is an inexpensive subscription service, and I would highly recommend it to those that want to advance their knowledge of birds beyond identification. Subscription information can be found RIGHT HERE.

No comments: