Wolves are skilled and ferocious hunters, but when it it comes to relationships, they're real softies. When a playmate or partner leaves the pack, the wolves that are left behind will howl and howl and howl.
In a new study, researchers report that wolves will give their leaders and their closest allies a longer and stronger serenade if they leave. Those howls could be sonic breadcrumbs, meant to help a lone wolf find its way back to the pack. They could also be a long-distance message that simply says: "I miss you."
"What exactly their motivation is, we will never know," said Friederike Range, an animal behavior researcher at the University of Veterinary Medicine in Vienna and one of the authors of the study in Current Biology. But "there is an emotional response in there, for sure," she told NBC News.
How much howling?
Range and her colleagues have been studying the group dynamics of timber wolves for years. In the newly published study, they observed how nine wolves from two packs living at Austria's Wolf Science Center changed their howling, depending on which member of the pack was absent from the group.
The researchers took each member of the pack away from the rest for a walk, and counted the howls from the remaining members for 20 minutes.
The howling would begin as soon as the departing wolf went out of sight. Wolves are social animals with a strict hierarchy. So if the wolf was a leader, more howls were recorded. And if the departing wolf was friendly with another member of the pack, its pack buddy sang a lengthy song.
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The calls are similar to "children calling for their parents when the parents leave," David Mech, an adjunct professor at the University of Minnesota who has been studying wolves since the late 1950s, explained in an email to NBC News. "To me it is communication."
Dogs, the cuddlier relatives of the wolves, also howl. But wolves are more socially savvy, and their howling serves more strategic functions.
Mech, who was not involved with the new study, once observed howling behavior in 15 wild wolves that were separated during a hunt. He described the phenomenon in his 1966 book "The Wolves of Isle Royale."
"After howling, the pack was then able to assemble again," he explained. Mack said the newly published study provides "experimental evidence" supporting his view that the wolves' howls helped them regroup.
Sometimes, wolves howl when they are stressed. Not these wolves. Range's colleague, Francesco Mazzini, tested the saliva of the howlers for cortisol, a hormone that's abundant in stressed-out animals. He found a slight increase in cortisol levels when a leader left, but no increase when the wanderer was a "preferred partner."
Wandering wolves who are leaders will often call back to their pack, but Range's wards didn't. While they were out and about, they ignored their packmates and just enjoyed the walk, she said.
More about animal communication:
Francesco Mazzini, Simon Townsend and Zsófia Virányi join Friederike Range as authors of "Wolf Howling Is Mediated by Relationship Quality Rather Than Underlying Emotional Stress," published online Thursday by Current Biology. The study appears in the Sept. 9 issue of the journal.
Nidhi Subbaraman writes about technology and science. You can follow her on Facebook, Twitter and Google+.