(Host) On Lake Champlain, one bird species is multiplying almost out of control. The double-crested cormorant was a rare visitor to the big lake just two decades ago. Now, almost 20,000 of the fish-eating birds are overrunning several islands and are pushing aside other bird species.
The state began shooting cormorants this summer. But as VPR’s John Dillon reports, a leading biologist is concerned that this attempt at bird control could backfire.
(Sound of a boat idling on the water.)
(Dillon) It’s about nine miles as the cormorant flies from Burlington Harbor to Four Brothers Islands on the western side of the lake. On this afternoon, a strong wing blows from the south. Beyond the breakwater, the lake has swelled to four-foot seas.
(Adam Duerr) “It’s going to be a wet ride.”
(David Capen) “I guess we’re going to buckle up here.”
(Dillon) University of Vermont biologist David Capen makes this trip frequently to monitor the movement of cormorants around the lake. Grad student Adam Duerr is at the wheel.
In 1981, Capen spotted the first nesting pair of cormorants on Lake Champlain. Since then, the population has exploded to about 20,000 birds. The ban on the pesticide DDT helped cormorants rebound. And in the southern United States, huge catfish farms have provided a winter bounty for the fish-eating birds.
The black cormorants look a little like loons or elongated ducks, but they’re actually closely related to pelicans. The birds prefer to roost in trees. But their acidic droppings eventually kill the trees and shrubby vegetation. Capen explains that without this habitat, other birds are forced out.
(Capen) “We’ve seen that over on Young Island very graphically over the years, where that island used to have a very nice population of black crowned night herons and cattle egrets and sometimes snowy egrets. And these are birds that nested in trees. There are no standing trees left on Young Island at all.”
(Dillon) The state owns Young Island and the Fish and Wildlife Department has worked with the UVM researcher to control the cormorant population there. In 1999, the state began applying corn oil to the eggs in the nest to prevent them from hatching. The egg-oiling continued for the next several years, and the population slowly dropped.
This June, officials tried a more direct approach. Wildife officers began shooting cormorants on their nests. Capen is the lead scientist working on cormorant issues on Lake Champlain. But he says no one told him when the shooting would start.
(Capen) “For that decision to be made and then the associated decision to be made that we’re not going to tell anyone, I think is out of character for the Vermont Fish and Wildlife Department.”
(Dillon) It’s not that Capen is sentimental about cormorants. He’s shot plenty of the birds himself, as part of a study to examine their diet by dissecting their stomachs. He wants to prevent the birds from overrunning other islands on the lake.
But he believes the shooting could backfire in several ways. Cormorants were driven off their nests by the daytime shooting. Gulls then ate the eggs. So if the cormorant population drops, no one will know if it was due to the gulls, the egg oiling or the shooting.
(Capen) “It wasn’t a very well run experiment if you look at it from a scientific standpoint.”
(Dillon) Capen says that the shooting also dispersed some of the birds to other islands around the lake. Some fly south to the Four Brothers Islands.
(Sound of boat coming into Four Brothers Islands.)
(Dillon) We ease into the lee of one of the Four Brothers and glide over a shoal of smooth black stones.
(Capen) “This is the island that most people are looking at these days. If you’ve been on the lake much, if you’re a sailor, that island was covered with healthy white pine trees. It was a beautiful forest eight or ten years ago. So it’s declined very quickly. We do now have cormorants nesting on all four of these islands.”
(Dillon) We splash ashore and Adam Duerr sets up a spotting scope to look for birds that researchers have banded over the years. He spies one that had been at Young Island before the shooting started.
Hundreds of gulls hover in the breeze. Each dead tree hosts several families of cormorants. The wind manages to carry away some of their smell. Duerr points out a patch of mint growing among the thistle and stinging nettle.
(Duerr) “I’m not sure what species it is. But as you’re walking around a colony that has 1,200 hundred pairs of cormorants, so 2,400 cormorants plus their young, the guano accumulates. It reeks. And walking through a patch of mint, it’s nice. It’s a refreshing treat.”
(Dillon) Duerr has a goofy sense of humor, a necessary trait for someone who gets up close and personal with cormorants. He’s banded birds at night and examined their stomachs to see what they’ve eaten. To the relief of Lake Champlain fishermen, his study showed that cormorants mainly prey on yellow perch and rainbow smelt – not the popular game fish like salmon or lake trout.
(Duerr) “Over the last three years, we’ve collected 160 birds and we haven’t found any of the salmonids, the trout or salmon, in the diet at all.”
(Dillon) But cormorants have clearly overrun habitat for other birds. Black crowned night herons have been driven off Young Island and may soon be gone from Four Brothers as well.
Degradation of the habitat is a concern for the Nature Conservancy, the national conservation group that owns the islands. While Duerr and I have been talking, Capen has shuttled to the New York side to ferry some Nature Conservancy visitors to their island. Chris Maron is the program director for organization’s Adirondack chapter. He says the Conservancy is weighing its options on cormorant control.
(Maron) “I think the whole population is a concern to us. And the Nature Conservancy prides itself on being a science-based organization. So we’re working to talk to the experts like Adam, like Dave and like people across the country to get the input so we can make the best decision about the cormorants out here.”
(Dillon) As gulls soar overhead and the black cormorants dive in the water, Dave Capen says the shooting eliminated some birds, but also moved others around the lake.
(Capen) “We know the immediate effect. We saw a number of birds from Young Island out here last week that just came here. And that didn’t surprise me a bit, because from what we’ve learned on cormorant movements if they lose a nesting attempt someplace, one of the first thing they’re going to do is go around at other places, probably surveying where they’re going to go next year.”
(Dillon) The state says officials resorted to shooting the birds because the other measures just weren’t working well enough. John Gobeille is a district wildlife biologist.
(Gobeille) “It’s not like we take a lot of enjoyment doing this. It’s kind of the ugly side of wildlife management. But we feel we need to do something because that pressure on the islands is going to be there if you don’t do something about the population.”
(Dillon) Gobeille says that Capen should have known that the shooting would take place, since it was discussed at a meeting this spring. He doesn’t believe that shooting the birds will accelerate their spread around the lake.
(Gobeille) “These birds are moving around without any disturbance anyway. It remains to be seen whether our culling impacts are going to exacerbate that movement more than what would occur naturally anyways.”
(Dillon) Back on Four Brothers, Capen says cormorant control is a multi-state and international issue. Birds that were banded in Vermont are increasingly showing up in Quebec. Others from Lake Ontario have made Lake Champlain their home. So even if the Champlain population is brought under control, birds will still feed in from the Great Lakes.
(Capen) “Some of the colonies which are much larger than all the birds we have here on Lake Ontario are still continuing to grow at a pretty rapid rate. So I’m not sure the whole Great Lakes population is leveling off.”
(Dillon) Both Gobeille and Capen agree that the goal is to have a more regional and coordinated approach to controlling the birds before they overrun more islands on the lake.
For Vermont Public Radio, I’m John Dillon.