The Department of Conservation believes starvation is killing little blue penguins on the west coast of the North Island.
About 50 blue penguins have been found on Taranaki beaches and a similar number in Waikato.
The department says the cause of their deaths came as a real surprise as there appears to be plenty of food around for them.
New Plymouth marine supervisor Bryan Williams told Summer Report that just why it was happening was a mystery at this stage. Further investigation was required.