Assisting the Common Tern
by John Grones | July 11, 2006
This past week three staff members from Rice Lake National Wildlife Refuge made their routine trip to very small islands on Mille Lacs Lake to monitor the breeding success of the common tern. The trip took us to Hennepin Island and Spirit Island. The two islands are both less than an acre, and they make up the smallest National Wildlife Refuge in the United States–Mille Lacs National Wildlife Refuge.
According to Rice Lake National Wildlife Biologist Michelle McDowell, the primary purpose of their visits are to assist common tern productivity because the bird is on the state’s list of threatened species.
The common tern is so rare in Minnesota, there are only four breeding colonies in the state, one of which is Hennepin Island.
During the early 1930s, there were approximately 2,600 nesting pairs of common terns in Minnesota. By 1984 the number had dropped to 861 breeding pairs statewide, and by 1988 that number was as low as 609.
With the decrease in nesting pairs, a project to assist the common tern on Hennepin Island began in 1993 with the assistance of the Mille Lacs Band of Ojibwe Department of Natural Resources. The project includes installing a gull enclosure (deterrent) grid over the gravel beach portion of Hennepin Island during the nesting season. The grid acts as a barrier to ring-billed gulls which compete for nest sites with terns; the grid lines are spaced to allow common terns access to the island.
Prior to arriving at the island, Michelle noted that they would be counting the number of nests on the island. “We will also count the number of eggs and chicks in each nest,” said Michelle. “We will also be checking in on the ring-billed gulls and the double-crested cormorants that nest there.”
Michelle was accompanied by Biological Technician Jacob Randa and refuge volunteer Ricky Bokovoy. The three enjoyed a beautiful day on the lake, and there were several nests, eggs, and chicks to count on the island. The process took approximately two hours. Michelle pointed out that it was very important to watch our step. “There are so many nests out on that island, that every time we set our foot down we have to make darn sure that we are going to miss a nest,” she said. “That’s one of the reasons the island is closed to the public.”
Michelle and her assistants also tightened up the string on the gull deterrent grid system. Michelle noted that the gulls are one major threat to the common tern because they compete for nesting sites. The weather is another factor. There was low productivity on the island last year due to a series of storms in June. Winds reached 80 miles per hour along the shore, destroying nests and killing chicks.
“Before the storms on June 25, there were 177 tern nests and 28 chicks under a week old,” said Michelle. “When we returned to Hennepin Island on July 6, only six chicks remained. The deterrent grid had been ripped up by the storms.”
According to Michelle, disturbance by humans can also result in the abandonment of nests. “We ask the boaters during nesting season to stay 200 feet or more from the island, just to give those birds room to nest and raise their young.”
Our second destination on the day was Spirit Island to check on the double-crested cormorant populations. “The cormorants have been nesting there for several years,” said Michelle. “About the time the project started on Hennepin Island with the grid, is about the same time cormorants started nesting on Spirit.”
“They hadn’t nested on either island before, and the colony has grown since then, and a few cormorants have nested on Hennepin Island. We do control work on Hennepin to protect the common terns, but on Spirit Island we’re just monitoring.”
The results of their monitoring–195 double-crested cormorant nests, 273 chicks and 41 eggs. A few ring-billed gull and herring gull nests were also found.
“The colony has grown, but the island is very small,” added Michelle, “so there has to be a maximum number of cormorants that can nest there.”
All in all, the nesting on the two islands was very favorable. “It looks like the terns are doing very well this year with 124 nesting common tern pairs, 119 eggs, and 96 chicks that have already hatched,” concluded Michelle. “The tern colony on Hennepin Island will continue to be checked every week, by us or the Mille Lacs Band of Ojibwe Department of Natural Resources until mid-August, and then we will pull up the grid.”
This article first appeared in the July 11 issue of the Voyageur Press.