Police are "following strong lines of inquiry" into the deaths of five critically endangered gulls.

Five black-billed seagulls were found dead at Rotorua's Sulphur Bay during a routine check by a Department of Conservation volunteer in mid-November last year. They are the most endangered seagulls in the world.

An x-ray of one of the birds found a BB bullet lodged in its breast.

Images of two men with firearms were taken from motion-detector cameras set up to monitor the colony and had been released in an effort to identify the pair.

Advertisement

The cameras were set up at the protected breeding colony by Department of Conservation to record colony activity and any threats to the birds.

Rotorua police area prevention manager Inspector Brendon Keenan said, from the images, the likely charges would be related to cruelty to animals.

"But also concerning was the discharging of the firearm," said Keenan.

The black-billed gulls were the most endagered gull species in the world.

They were classified as critically endangered by the Department of Conservation which was one step away from extinction.

Department of Conservation senior ranger of biodiversity Mariana Te Rangi said the alleged killing of animals by people was a preventable and unacceptable risk.

"These special birds are a taonga to Rotorua and are threatened with extinction.

"As the black-billed gull is the most endangered gull species on the planet, DoC is treating the incident seriously.

It was an offence, under the Wildlife Act 1953, to disturb protected birds and destroy nests. Doing so could result in imprisonment and/or a fine of up to $100,000.

About the Black-billed gull/tarāpuka

- The most threatened gull species in the world.

- Endemic to New Zealand.

- Like the Kākāpō, it is the stage before extinction: the current threat status was upgraded from Nationally Endangered to Nationally Critical in 2013. The same level as the Kākāpō.

- Breeding sites are mainly large braided riverbeds of the South Island but there are scattered colonies in Hawke's Bay and Wairarapa, as well as Lake Rotorua and Lake Taupō.

- Wide range of threats: cats and stoats, farm herbicides and pesticides, riverbed weeds forcing nests closer to the water, making them more vulnerable to flooding.

- Humans threats more common in recent years with vehicles and shooting.

- The birds are more slender than the red-billed gull, with a longer bill.

- There has not been a successful fledgling of chicks for six years from the Sulphur Point colony.