Duluth, Minn. — Don Carlson and Nancy Drilling circle around Knife Island in Lake Superior and choose a place to land.
"Nancy, if you want to start the count right here, I'll walk through the brush down the center and through the backside," Carlson says. "And I should meet you right over there, at the end of the island."
Carlson hooks the anchor on a rock on the shore.
Cormorants share this island with hundreds of gulls. When the humans land, most of the cormorants fly off. But the gulls hang around, complaining about the intrusion.
Carlson and Drilling speak quietly to avoid upsetting any cormorants still in the nests. And they walk carefully to avoid stepping on nests on the ground.
Drilling says young cormorants sometimes don't do a very good job building their nest.
"Some can be very inexperienced; they just throw a few sticks together and it's flimsy," she says.
Most of the nests seem sturdy. They're near the tops of dead trees. In some places, the cormorants' droppings can kill trees over time. That's one reason people don't like them. But Drilling says these trees probably died from something else.
Each time she spots a nest, Nancy Drilling clicks her counter. When she meets up with Don Carlson, they arrive at a total for the island.
"We've got 15 down here, so that's 25 nests."
Then it's back to the boat. The researchers want to leave quickly so the parents can come back and take care of their chicks.
As they motor away from the island, Nancy Drilling watches the adults fly back. "They come back right away," she says.
Drilling and Carlson have criss-crossed Minnesota this summer, tracking down cormorant colonies.
Francie Cuthbert teaches at the University of Minnesota. She's an expert on cormorants. She says they're unusual birds.
For instance, they sometimes cooperate to catch fish.
"No-one's done any underwater photography that I know of," she says. "But it appears that as a group - and it could be a dozen birds or it could be several hundred birds - they will swim and push a school of fish in front of them, and then individuals will break off from the group of cormorants, and go to the front and capture the fish that are being pushed in front."
Whether they're herding fish, or diving deep to catch them, cormorants are good at fishing. They can catch and eat a pound of fish a day.
Of course, they're not the only big birds out there eating fish. Francie Cuthbert says pelicans can eat four times as many fish as cormorants. But people seem to be much more upset about the cormorants.
"People historically have had negative feelings about black birds, as being ominous," she says. "Cormorants also have a long thin neck, and some people refer to them as snake birds. So it kind of all comes together as a very negative perception."
Cuthbert says the number of cormorants in North America has gone up and down over the years. In the 1950s and 60s, cormorants, like bald eagles, were were hurt by DDT. But in 1972 the federal government banned DDT, and in the same year, began protecting cormorants, along with other migratory birds.
In the Great Lakes region, cormorants feed on many fish, including two exotic species, smelt and alewives. And in their winter home in the southern states, the birds began feasting at the new commercial fish farms.
So in the last thirty years, cormorants seem to be making a comeback.
But this is the first time anyone has counted cormorant nests all over Minnesota in one summer. Results of the count should be in later this month. Researchers will use the numbers as a baseline, and plan to do more counts in the future.