Killer whales appear to be inviting humans for lunch, a new study suggests.

The research investigated unusual occurrences of orcas in four oceans attempting to share prey with people.

More than 30 cases were documented over two decades where the wild orcas offered people a range of freshly acquired fishes, mammals, and even invertebrates. The whales approached people, dropped the item, and awaited a response.

The authors conclude that these cases provide opportunities for orcas to practise learned cultural behaviour, explore or play, and in so doing learn about and potentially develop relationships with people.

Having witnessed these events themselves, the authors also provide some ideas about how this behaviour might have evolved and the implications of such interactions.

Lead author Jared Towers says: "There appears to be a prosocial element to these cases indicative of interspecific generalised reciprocity which is extremely unusual to witness in any non-human animal and is suggestive of evolutionary convergence between orcas and people."

Second author Dr. Ingrid Visser says: "Orca are very social and we frequently see them food-sharing. To document and describe behaviour of them attempting to food-share with humans in various places around the globe is fascinating."

Third author Vanessa Prigollini says: "Orcas are apex predators that often eat other large mammals, but when it comes to people, they occasionally prefer to share, indicating their interest in building relationships outside their own species."

Ecologist and author Dr. Carl Safina, who was not involved in this study, says: "Of the many and varied minds in the sea, likely the greatest are those of orcas."

"Casual stories of their almost surreal intelligence abound. But here these scientists have systematically gathered an impressive litany of instances where free-living orcas have shown that they possess ‘theory of mind,' meaning that their minds understand that humans have minds too."

"After living millions of years in the sea, to them we in our boats must seem like visiting aliens. And indeed, we are strangers in a strange place we hardly know, about which we yet have almost everything to learn."

The study will be published open access on 30 June in the Journal of Comparative Psychology.