With no visual facial expressions to signal their intentions, animals may have evolved laughter-like sounds to reassure others that they are not being aggressive.
Animals do the most amazing things. Read about them in this series by Janaki Lenin.
At one time, laughter was one of the attributes that elevated humans from the rest of animal kingdom. By making laughter-like noises, chimpanzees, macaques and rats broke that barrier. Kea, a species of large parrot from New Zealand, warble to show playfulness. Researchers found this call infectious, a first for a bird. When other kea hear these calls, they can’t help becoming frisky.
The olive green parrots that live in the mountains of South Island in New Zealand spend a lot of time playing. They jostle, kick and bite their partners, sometimes dragging them across the ground. They roll on their backs, treading the air with their feet while their partners jump on their tummies. After locking their long hooked bills, they twist and push, performing a bird version of arm wrestling.
They create toys out of inanimate objects, playing tug of war with rocks or sticks. They are so comical that they earned the epithet ‘clever clowns of the mountains.’ The urge to play is ingrained strongly and if one partner attempts to stop, the other protests. While they play, they make a distinctive warble that researchers describe as play-call.
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Was this call an invitation to play? Dogs perform the play-bow, crouching low with their heads touching the ground and their rear ends held high, to invite another to a game. The kea solicit play, too. They tilt their heads to one side while hopping in short oblique steps towards their partners. They then roll on their backs, inviting their mates to play. Would the warble-laugh be the audio counterpart of this invitation?
Doctoral student Raoul Schwing, University of Vienna, Austria, investigated the call’s role in kea games. He had already explored the vocal repertoire and scavenging habits of the bird. At Arthur’s Pass National Park, New Zealand, Schwing targeted wild kea that weren’t playing. He played four recordings through a speaker for five minutes and observed their behaviour. The sound recordings included the play-call, a kea screech and whistle and the song of another bird, the South Island robin. He watched their behaviour before and after playing the recordings to gauge any changes.
When the kea heard the play-call, they didn’t join other birds that were already playing. Instead they started playing with birds that were closest to them. If they were alone, they played with any object they found or performed aerial acrobatics. But they didn’t react to the other sounds.
“When I saw a kea spontaneously pick up a rock and start playing with it, I knew we had found something special,” Schwing told The Wire.
He and his team of colleagues and supervisors concluded that the play-call is not an invitation to play. Instead, it prompted them to play – like infectious laughter.
“This study is however not showing any evidence of ‘laughter’ being contagious, in contrast to what the authors claimed,” Marina Davila-Ross, University of Portsmouth, UK, told The Wire. “Claims on hominoid ‘laughter’ are based on phylogenetic analyses and therefore it is acceptable to use this anthropomorphic term for our closest relatives. Such phylogenetic reconstructions have, however, not been carried out beyond great apes.”
However, scientists studying play in rats and Barbary macaques use the word ‘laughter’ without tracing the evolutionary history of these species. In the kea study, Schwing and his colleagues use the word cautiously. “We did not say that kea play calls are laughter, or share any similarities to laughter beyond what has already been suggested for primates and rodents,” Schwing clarified.
So why did this laughter-like behaviour evolve? Unlike humans and bonobos, when chimpanzees, macaques, and rats play, they don’t grimace. With no visual facial expressions to signal their intentions, animals may have evolved laughter-like sounds to reassure others that they are not being aggressive. Kea may have evolved their playful warble for similar reasons.
“We theorise that it acts as a social facilitator, making social interaction more peaceful in the group,” says Schwing. It may tell other kea that the caller is in a playful mood and means no harm.
Young kea form flocks, called circuses, of up to 20. Although they pair for life as adults, they congregate as a circus in feeding areas. Misunderstandings are the bane of social gatherings, so the warble-laugh may be the clearest signal of playful intentions.
In most animals, no-nonsense adults have little time for frivolous activities like play. Adult male and female bonobos play during courtship. African hunting dogs and timber wolves frolic to strengthen their packs’ social bonds. Otherwise, adult animals rarely play with members of the opposite sex. But adult keas of both sexes need no excuse to play.
“Little is understood about why animals play in general,” said Schwing’s supervisor and co-author, Ximena Nelson. “But kea are unusually playful at all sex and age groups. Perhaps they evolved with relatively few predators – their main predator might have been a now-extinct Haast eagle with a wingspan of about three metres – so there may have been relaxed selection on ‘leisure time’, especially in the spring when food is plentiful.”
When the researchers set out to test the function of the play-call, they didn’t expect to find it infectious. “The fact that at least some of these birds started playing spontaneously when no other birds had been playing suggests that, similar to human laughter, it had an emotional effect on the birds that heard it, putting them in a playful state,” Schwing said in a press release.
In effect, for kea, hearing the warble playback would have been like hearing canned laughter in comedy soap operas. Just as hearing taped guffaws puts us in a jovial mood, the play-call may put the birds in a frisky mood. “Most play-calls were not described as having such an effect,” he said. “We assumed it would fall more inline with the more common effects of play invitation.”
Davila-Ross does think this is an interesting and important study. “The findings are particularly convincing as the birds were previously not involved in social play,” she said. However, on hearing the play-call, kea played only for a few seconds. For a bird that seems to live to play, why were the bouts of playing so short?
“I think that the drop of play was based on the generally unfavourable weather conditions,” explained Schwing. “If we had conducted the experiment in summer, the effects might have been much longer lasting, as the natural propensity to play would have been higher.”
Conducting experiments with a species as smart and curious as kea can be aggravating. Nelson says one of the challenges of doing the study was preventing the birds from destroying their audio playback equipment. They had to ‘kea-proof’ the speakers with thick wire.
Their study was published on March 20 in the journal Current Biology.
Janaki Lenin is the author of My Husband and Other Animals. She lives in a forest with snake-man Rom Whitaker and tweets at @janakilenin.