Hundreds of little blue penguins have washed up dead on the shores of New Zealand in recent weeks, and researchers think warmer waters that are affecting their food supply may be the culprit, NBC reports.

Driving the news: Mass deaths of the flightless birds, also known as korora, once took place roughly every 10 years, Radio New Zealand reported. Over the last six years, researchers have documented three separate die-offs.

• The penguins were tested for diseases, but researchers believe they died from starvation, said Graeme Taylor, a principal science adviser with the New Zealand Department of Conversation.

What they’re staying: The birds found on the beaches are “just skin and bones,” Taylor said, per Radio New Zealand.

• "They've got no fat on their body. They need that insulation of the fat layer to keep them warm,” Taylor said. “And they haven't got that [and] they haven't got much muscle tissue on them."

State of play: With ocean temperatures warming, the small fish the penguins eat to survive seek cooler waters elsewhere or retreat farther below the surface, to depths beyond where the little penguins are capable of diving.

• La Niña may have something to do with it, as well, Taylor said.
• The weather event spurs lower ocean temperatures in parts of the Pacific around the equator and brings warmer water temperatures to northern New Zealand, where the penguins have washed up.

Zoom out: Last year was the hottest ever recorded in New Zealand, according to data tracked by the National Institute of Water and Atmospheric Research.