The Department of Conservation is investigating the mass killing of gulls considered the rarest in the world.
More than 100 black-billed gulls were found dead near Wrey's Bush in Southland in November.
DoC spokesperson Jessica Bernard told Checkpoint autopsy results returned this week from Massey University and show most of the birds were shot.
Ms Bernard says shotgun shells were found on a riverbank where the gull colony was based.
The rare inland species of gull is found only in New Zealand, she says.