(CNN) Authorities are investigating the "premeditated" theft of little blue penguins from a burrow in New Zealand's Hawkes Bay region -- raising concerns criminals are smuggling the birds.

One woman and two men were seen using a crowbar to capture three of the animals -- the world's smallest penguin species -- last Thursday, the country's Department of Conservation said in a news release.

One of the penguins died and was left behind.

A second dead penguin was found with what appeared to be head injuries the following day, Conservation Department compliance officer Rod Hansen said.

"In our view, it's likely premeditated. It's not just some teenagers," Hansen told CNN.

Little blue penguins typically weigh about 1 kilogram (2.2 pounds) and are only 300 millimeters (11 inches) long. They are the most common penguin species found across New Zealand's mainland, and are protected under the country's Wildlife Act.

Hansen said he wasn't aware of illicit trading of little blue penguins, but couldn't rule it out.

"We don't have any reason to believe they're being smuggled across the border. But it's a possibility. We just don't know," he said.