Four critically endangered birds were killed during a bird cull in New Zealand on Aug. 17. The birds, called takahe, were apparently shot by members of the New Zealand Deerstalkers Association contracted by the Department of Conservation to kill pukeko, a similar looking but overly populated bird, The Guardian reports.

The bird cull was carried out on Motutapu Island, supposedly to target pukeko, which grows abundantly and is a threat to native bird species. However, when DOC staff examined the birds killed by the deerstalkers, they were horrified to find four takahe among the slain birds.

Takahe birds are often mistaken to be a fat pukeko because of the similarity in their appearance. There are only about 300 takahe left in New Zealand, and in Motutapu Island there were only 21 takahe before the shooting happened, according to Stuff.

The DOC called for an immediate halt of the bird cull after the incident. DOC director Andrew Baucke said the takahe's deaths were "deeply disappointing."

"The hunters had been carefully briefed on how to differentiate between the flightless takahe and pukeko, including instructions to only shoot birds on the wing," Baucke explained, according to ABC.

In 2008, a similar incident happened on Mana Island when a conservation worker mistook a takahe for a pukeko and shot it. Because of what happened, bird cull guidelines were implemented to protect the critically endangered bird species.

"I share with the department a concern that the deaths will affect efforts to save an endangered species," New Zealand Deerstalkers Association president Bill O'Leary said. "I apologize to the department and to the country at large," he told New Zealand Herald.

Conservation Minister Maggie Barry said she was "deeply saddened and very disappointed" by the incident. 

"I ... have been fully briefed by DOC. It is under investigation and I can't comment further at this stage," she told Stuff.