Meanwhile in Norway, orcas share their food after a group hunt

Three decades of research has confirmed one thing about the appetites of Norway's killer whales: they love Atlantic herring. The orcas here feed almost exclusively on the small, silver fish – but new drone footage proves that some rogue groups prefer a mammalian meal. Not only do the members of these unique pods hunt seals, but they also share them with each other.

This stunning footage was captured by researchers at the Norwegian Orca Survey (NOS), who are in the midst of a lengthy study that aims to crack open the habits of the region's seal-eaters.

To be clear, orcas in other parts of the world – namely a population known as the "Transients" or "Bigg's" in the Pacific – do eat mammals, but in Norway, this behaviour was observed for the first time only in 2014. "We finally got to capture [it]," the team wrote on Facebook. "To our knowledge, such images by drone are unique and may be a first worldwide."

The NOS team has been watching this particular group for three years, and the emergence of drones has made that effort significantly easier. Unlike noisy research boats, the sky-high tech goes largely unnoticed by passing whales, but drones also have another leg-up on traditional, manned vessels: polarized lenses allow them to see what human eyes cannot.

"Drones enable observations of activities that may occur within the first meters below the surface, yet completely out of the observers' sight," write NOS researchers Eve Jourdain and Richard Karoliussen in a guest blog at ZME Science.

This is exactly what happened during the seal hunt. After a typical coastline cruise, the team noticed that the largest male in the orca group had begun to show behaviour associated with hunting (sharp turns, explosive breaths and highly arched dives), but the researchers realised what was going on only when the drone picked up the seal's presence in the water.

"The five killer whales were persistently circling it, leaving it with no chance to escape towards the haul-outs nearby," the researchers explain. "For a few minutes, the sea surface remained quiet. The seal may have escaped to the bottom where cavities and rocks offer hiding places. Yet killer whales are skilled top predators able to cooperatively search and handle all prey types and, eventually, the group came up back to the surface with the prey: dead."

Then came the second surprise: the orcas proceeded to take turns at the carcass. "Food-sharing has been previously highlighted in other killer whale populations," explain Karoliussen and Jourdain. Among fish-eating killer whales, for example, it's common for a mother orca to hold salmon in her mouth while her calf has its fill.

Why share food? When each member of the group is fed and healthy, the pod improves its chances of landing prey, producing healthy offspring and defending each other from predators. It's a common strategy among many terrestrial pack animals, but seeing it play out among orcas is a treat made possible by new drone technology.

"The oldest female of the group could be seen leading the [seal] carcass towards the surface and taking the first bites out," recalls the team. "She then deliberately dropped the carcass, leaving an opportunity for the rest of the group to join the feast." The spectacle went on for 15 minutes, during which time, five members of the pod fed from the carcass.