Since April, marine science professor Lucy Vlietstra and three of her students have been visually counting the number of common terns and endangered roseate terns that fly into a 150-foot zone around the turbine, called the airspace.

Although the turbine was officially activated on June 23, the academy has shut it down periodically for the bird study.

The researchers have found that more birds fly into the airspace when the turbine is turned off than when its blades are spinning.

"We need more time to look at how strong a pattern it is," Dr. Vlietstra said.

She said the terns' feeding behavior has not changed, but that they "seem to avoid close proximity" to the turbine when it is moving.

The academy is cooperating with the Natural Heritage and Endangered Species Program of the state Division of Fisheries and Wildlife on the study, which will continue through November.

As part of the study, researchers regularly survey the area beneath the turbine looking for evidence of bird strikes.

So far they have no reason to believe any birds have been injured or killed by the turbine, Dr. Vlietstra said.

The academy's turbine is the first state-owned turbine of commercial size. Built by Boston developer Jay Cashman, it will supply a third of the academy's annual power needs and reduce oil use by about 20,000 barrels per year, said school president Rear Adm. Richard G. Gurnon.

Concerns for the safety of birds and bats are slowing construction of wind farms around the country. Some existing wind farms have shown evidence of bird kills.

A study of the Altamont Pass Wind Resource Area in California found that more than 4,000 wind turbines were responsible for killing between 881 to 1,300 birds of prey each year. The report by the California Energy Commission showed that the resource area — which spans an international migratory bird route — killed golden eagles, red-tailed hawks, American kestrels and burrowing owls.

Environmental groups are suing the turbine owners to force them to take corrective measures to mitigate bird kills.