Northern bottlenose whales have stronger social bonds when they are starving or sick. This discovery was a surprise, because often in mammals, social connections are associated with better health. But during tough times, these whales may rally round and care for others in need.

That idea fits with early whalers’ descriptions of the animals’ behaviour. In a report from 1882, David Gray, commander of the whaling steamer Eclipse, said he had observed thousands of northern bottlenose whales, and noted they had a peculiar response to injured individuals. “The herd never leaves a wounded companion so long as it is alive,” he said. “They come from every point of the compass towards the struck one in the most mysterious manner.”

But such observations are hard to make. Northern bottlenose whales (Hyperoodon ampullatus), which belong to a relatively mysterious whale family known as beaked whales, live in isolated parts of the ocean and spend most of their time diving deep for food. “Seeing and studying this elusive species is not easy at all,” says Olaf Meynecke at Griffith University in Brisbane, who wasn’t involved in the research.

But Hal Whitehead at Dalhousie University in Halifax, Canada, and his colleagues have been studying a local group of northern bottlenose whales since the 1980s. This population is centred over a deep submarine canyon, a day and a half sail from Halifax.

The team has collected a database of photographs, taken as the animals come to the surface, stretching back 37 years. Different whales can be identified in the pictures from markings on their fins, providing a rare opportunity to track their lives over decades, says team member Sam Walmsley at Princeton University.

The researchers recorded whether the whales looked plump or emaciated, as a marker for health. Around 11 per cent of the whales were classified as being in poor condition at any particular time. To map their social relationships, the researchers recorded which companions the whales appeared with in the photographs.

Walmsley expected to see a positive correlation between social bonds and health, as has been reported in many mammals, from mice to baboons. “If a whale is in poor condition, maybe it just needs to focus on getting enough squid [or] enough fish to survive,” he says, rather than investing energy in socialising. But, in fact, the sickly whales had more social partners than was normal for this species, and they hung out in larger groups.

The reasons for this are unclear. Maybe sick whales are more likely to seek out others, says Walmsley, or maybe whales that are already in bigger groups have to compete more for food. But an interesting possibility, he says, is that “the whales are attracted to these whales in poor condition, maybe providing some additional support”.

Caregiving would fit with what is seen or suspected in other cetaceans, too, says Meynecke, even if it can be hard to prove. Humpback whales, which Meynecke studies, aren’t particularly sociable, but they share information about food abundance and hunt together if times are hard, he says. “We are seeing that when they are stressed, they do assist each other.”

For Walmsley, the finding also helps to put human relationships into context, as evidence mounts for how damaging social isolation can be for our health. “I think getting more specific about how health and sociality are related in a wide range of mammals is part of what helps us to think about the evolutionary side of that,” he says.