Life in the pod: the social lives of whales
The behaviours of whales have endeared them to us like few other species on Earth.
Long-term research into the way they learn, hunt and socialise shows they may have more in common with us than previously thought.
Dr Luke Rendell, researcher at the University of St Andrews, has been working closely with Museum scientists for a new exhibition, Whales: Beneath the surface.
His research delves into the evolution of social learning, communication systems and culture among whales and dolphins.
'As biologists, when we talk about culture we mean behaviour that is learned from others and shared by a group,' Luke explains.
'We're not saying that whales have opera and dolphins have poetry, but some forms of shared and learned behaviour do seem to be very important to them in terms of how they make their living, survive, feed themselves and develop a sense of belonging.'
'These animals are learning from each other in ways that are very important to their societies and their survival.'
Several types of cetaceans live in close-knit family groups sharing knowledge, songs and hunting techniques. There is also evidence of them providing food for those less able to hunt.
Scientists have been investigating the meaning of whale song for decades. They have only just begun to decipher some of these underwater melodies.
It turns out that in whale communities, much like with humans, knowing the right tune can be a vital part of fitting in.
Most toothed whales, dolphins and porpoises make clicks and whistles, while baleen whales make deep, low calls that can travel vast distances across the ocean.
Cetaceans generate sounds to not only navigate the ocean and locate prey using echolocation but also identify themselves as members of a society.
Luke explains, 'Echolocation is part of the sensory biology of all toothed whales, but it is sensory - meaning it is used to aid hunting and navigation, rather than being communicative. Whale song is something else altogether.'
Whale song may work in a similar way to human accents.
'People who sound like you tend to make you feel at home,' says Luke.
Why do whales sing?
Whale songs mean different things to different groups of whales.
Depending on the species and specific group, songs can be signifiers of a range of relationships including eligible mates, familial ties, social affiliations and hunting styles.
What makes whale song so interesting to scientists is that songs are something whales learn from each other and which evolve over time - like our own taste in music.
Among the groups of whales studied, sperm whale dialects appear most stable. Gradual changes can be detected over years in killer whale dialects, while humpback whale songs can change completely in just one year.
Luke says, 'Over time, some populations will radically change their songs. It can't be explained through the loss of a single influential animal either - it's more like a gradual cultural revolution.'
According to Luke, part of what makes whale song something cultural is the process of change and learning from each other.
'We've found that song and calls can be used to negotiate nuanced relationships and what we understand to be complex, multicultural societies.'
Song is used differently across species. In humpback whales, which tend to be solitary, all the males in a breeding population sing the same song.
Among populations of sperm whales and killer whales, however, scientists have found animals of the same species with different dialects and distinct social groups living in the same waters.
The waters off Canada's west coast are home to a number of killer whale communities that use song to navigate surprisingly complex and nuanced social relationships.
Pods have unique calls for their family group as well as some they share with other groups.
'Pods that share at least one call type are called an acoustic clan,' explains Luke. 'It's quite a complicated structure. Pods in the same community that share calls will sometimes associate with each other. But pods that don't share calls don't tend to mingle.'
Calling behaviours also correspond to different hunting practices. Killer whale societies are strongly segregated, based on specialisations of diet, into what scientists call ecotypes.
'There are fish-eating types which might specialise in salmon hunting, and there are mammal-eating types which tend to follow the breeding grounds of pinnipeds like sea lions, seals, walruses or even penguins.'
'But there are strong social divisions even within those groups that eat mammals. They aren't part of the same communities either, as some specialise on different prey.'
Whale calls can be so specific and recognisable that their prey can use the sounds to identify danger.
A 2002 study on predator recognition found that grey seals could use the whales' calls to identify which pods were a danger to them.
Luke says, 'Scientists played back a range of calls from fish- and mammal-eating whales, and found that the seals could differentiate between pods that were and were not a possible threat.'
Killer whale groups also practice a rare form of philopatry, where both male and female offspring tend to stay with the group they are born into.
In virtually every other group of animals, one sex will leave the group, but in the fish-eating killer whales found in the north east Pacific we find a very rare case where neither of the sexes will disperse.
The social divisions between groups of killer whales with different hunting strategies and songs are so pronounced that scientists believe it is unlikely that groups socialise or interbreed.
'The divisions are so strong that when you look at DNA analysis there is evidence that divergent cultural hunting styles are having an evolutionary impact.'
Looking at the DNA of groups of killer whales that hunt differently, scientists believe they may be in the process of diverging into separate subspecies or even fully-fledged species.
'There is a lot more going on out there than we thought even ten years ago, and there is still a great deal more to know,' Luke says.