Plenty of animals sound an alarm when a predator comes near, but orangutans apparently prefer to wait until the threat has passed to inform those around them.
Researchers working in Sumatra's Ketambe forest draped tiger-striped, spotted or plain sheets over themselves and walked on all fours while a lone female with an infant sat in trees well above the ground. Once the researcher was spotted, he waited a couple of minutes before moving out of sight. The researchers waited for the female to sound an alarm — and nothing happened.
"She stopped what she was doing, grabbed her infant, defecated [a sign of distress] and started slowly climbing higher in the tree," Adriano Reis e Lameira, a postdoctoral student at the University of St. Andrews in the United Kingdom, told Science Magazine. "She was completely quiet."
But about 20 minutes later, the female did sound the alarm, and she did so for more than an hour. This was the longest Lameira and his colleagues had to wait for an orangutan to signal that danger had been present; the average was seven minutes.
Lameira and his team suggest in their study, published in Science Advances, that the delay in calling attention to danger isn't because the females are scared; instead, waiting is both a method of protecting the offspring and teaching it at the same time.
"The mother saw the predator as most dangerous to her youngster and chose not to call until it was gone," he explained. By waiting, the mother informs the infant about the danger after it's gone, protecting them both while also relaying news of the danger.
This suggests, according to Lameira, a high cognitive processing of the stimulus and general intelligence, to say nothing of the apes' ability to control their laryngeal muscles. These are traits that ultimately led to the evolution of language, Lameira told Science Magazine.
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