Double-crested cormorants are currently residing year-round on islands of Guntersville Reservoir where they were once winter-only dwellers—and their new summer occupancy is changing the landscape.
Guntersville birdwatchers have plenty to fill their binocular frames. Bald eagles and osprey are commonly sighted; golden eagles put in a rare appearance. American robins, various blackbirds and multiple species of swallows flock to the region. Loons, terns, herons and a variety of waterfowl in the region delight and amaze. But one bird in the area is newly available for viewing in abundance—the double-crested cormorant.
Double-crested cormorants, once a rarely seen migratory waterbirds, have now begun to set up permanent residence on the islands of Guntersville Reservoir, nesting in groups as large as 600 pairs. Wherever they nest in such large numbers, they can harm and even kill vegetation, including mature trees. Their highly acidic excrement can strip trees and shrubs of leaves and branches and kill grass in the areas where they nest in relatively short order.
Guntersvillians, rightly, are alarmed—about the change in the scenery, yes, and more. “We are concerned that the cormorant waste will contaminate the water in areas around the islands where people fish, swim and ski,” says Guntersville Mayor Leigh B. Dollar.
A New Phenomenon
This wasn’t always a problem in Guntersville; in fact, double-crested cormorants were once a rare summer sight throughout the southeastern U.S. As with many raptors and wading birds, numbers dwindled in the years before hunting and pesticides such as DDT were regulated. But since the 1980s, populations have rebounded.
Even so, until recently, residents of Guntersville have had no problems with cormorants, as the area has long been a short over-winter, or even fly by, for this particular winged species, which has historically preferred spending the colder months in the southern-most portion of the U.S. and Mexico. Cormorants usually fly north for the summer to nest in the northern United States and Canada.
However, the bird has apparently seen something in Guntersville—something it likes enough to not only winter here, but stay for the summer as well. No one knows exactly why, but it’s easy to speculate. “They have everything they need here,” says Natural Resources specialist R.J. Moore, who’s leading a research effort to study why the cormorants are staying put; what kinds of damage they are doing to vegetation, soil and water; and how populations can best be encouraged to move back to their migratory ways. “They have cover, shelter, food and space all in one place—and if you have delicious food, fixed and on your plate, you’re not going to go out to a restaurant, right?”
The resident birds are causing an imbalance on Guntersville, one that’s in turn causing a strain on natural resources there. It’s a relatively new phenomenon; requiring study to find an answer. Partners involved with the Guntersville cormorant projects include Mississippi State University, the USDA-Wildlife Services, the Alabama Department of Conservation and Natural Resources, and the Marshall County Legislative Delegation, along with many other regional and local groups.
Research Done Right
TVA is a key player, being a public steward responsible for some of the Guntersville lands and islands showing impacts. And TVA is taking a measured, scientific approach.
Project efforts include:
- Comparing soils from inhabited islands versus uninhabited islands
- Continuously testing water quality near inhabited islands
- Comparing vegetation change/response to impacts and various management techniques within local population
- Placing trackers on birds to monitor their movement patterns
- Comparing prey isotope values in muscle and tissue samples from marine versus freshwater systems to help determine the percentage of migratory versus resident birds
- Studying whether prescribed burns can help re-establish lost vegetation and break down defecation deposits on inhabited islands
“We are going about our efforts very strategically, and always with a mind toward, ‘How can we find balance?’” explains Moore. “This is an ongoing project for TVA and its partners, and it will serve as a learning experience. We are already starting to see nesting numbers increasing at other reservoirs. We hope to develop a practical, feasible cost-effective management tool—one that we can share with other resource managers who may be faced with some of the same issues in the future.”
He sums up his work thus: “That’s the whole point of research—finding a good scientific basis to provide guidelines for doing the right thing and executing properly.”
It’s not clear yet what that thing is, though the overall goal is zero nesting pairs within the local population. So for the cormorants it may simply boil down to this: Get back to your migratory patterns, and get back up north for the summer for breeding season.
See you next winter, feathered friends.
Cormorant Study Partners
TVA is working with many partners to study how best to control cormorant populations on Lake Guntersville. Among other local and regional partners, these include: