Three recent incidents of orcas seemingly attacking and sinking boats off the southwestern tip of Europe are drawing intense scrutiny over whether the animals deliberately swarmed the vessels and if they are learning the aggressive behavior from one another.

Encounters between orcas, or killer whales, and boats have been increasing since 2020, though no human injuries or deaths have been reported. In most cases, the whales have not sunk the boats.

The string of incidents since 2020 prompted one scientist in Portugal to say the attacks may indicate that the whales are intending to cause damage to sailing vessels. Others, however, are more skeptical, saying that while the behavior may be coordinated, it’s not necessarily coordinated aggression.