A breeding pair of wedge-tailed eagles has been killed at Roaring 40s' Woolnorth Bluff Point windfarm in the state's north-west.

A spokesman for Roaring 40s said the company "gets as upset as anybody when there is a collision", but urged people to keep the deaths in perspective.

The first eagle was killed on August 17 and a few days later its mate was also struck.

The company spokesman said the second bird was struck as it fended off a second eagle pair trying to moved into its territory.

"It was extremely aggressive behaviour from the two eagles. It was something we had not seen before," he said.

Eagle monitors were on site and had shut down part of the windfarm because of the presence of the eagles, but that still was not enough.

The injured eagle was taken to a vet and euthanised.

The company said the deaths were the first at the Bluff Point site in almost two years and brought the total number to 12 since the windfarm was fully commissioned in 2004.

The spokesman said the deaths were devastating for workers who were on site purely to watch out for eagles.

But he said windfarms accounted for a very small number of the estimated 165 premature eagle deaths each year.

The company invests more than $1 million a year on measures to prevent eagle deaths on-site, as well as wider conservation projects.

Birds Tasmania chairman Eric Woehler said Roaring 40s had "done a lot of good work to minimise eagle strikes".

"But every death of an endangered species is one step closer to the extinction of that species," Dr Woehler said.

Greens environment spokeswoman Cassy O'Connor called on the State Government to investigate the deaths "and ensure the public are informed of the outcome of that investigation, including what is being done to reduce eagle mortalities at Woolnorth".