The Department of Conservation says starvation not rat poison is to blame for penguin deaths in Auckland's Hauraki Gulf.
There had been some speculation that the deaths, and those of five pet dogs, were connected to a pest eradication operation on Rangitoto and Motutapu islands.
Of the five blue penguins tested, only two were found to have small traces of rat poison in their systems.
However, the department's area manager, Brett Butland, says it is concerning they ingested any at all.
He says it is too early to say whether the department will review its bait-dropping procedures.