The mystery as to why wolves howl has been uncovered, researchers said in a recent study, BBC News reported.

The study, published Thursday in Current Biology, suggests wolves howl when a close friend or a high-ranking member of a group leaves. The discovery enforces wolves' (and dogs') identity as social and loyal animals.

The findings are more social than psychological, co-author Friederike Range from the University of Veterinary Medicine Vienna, Austria, said. The howl was a way for them to communicate to each other how much the member meant to the pack.

"We didn't know there was some flexibility on how much they howl depending on their relationship," Dr. Range said. "The amount of howling is really defined by the quality of the relationship."

A lead author on the study, Dr. Simon Townsend one of the lead authors from the University of Zurich, Switzerland, said the wolves howled more for higher-ranking members.

"Wolves seem to howl more when higher ranking individuals leave because these individuals play quite important roles in the social lives of wolves," he said. "When they leave it makes sense that the remaining wolves would want to try and re-initiate or regain contact. The same applies for friendship."

The researchers studies nine wolves from two packs in Austria's Wolf Science Center. They found that a wolf would not howl unless the companion was taken far away, implicating a permanent leave. The scientists analyzed cortisol levels in the wolves' saliva to measure their levels of stress. Through this, they determined the howls were not psychological, but rather socially motivated.

"What we expected was higher cortisol levels if the wolves were more stressed when 'friends' leave, but what we found is that cortisol doesn't seem to explain the variation in the howling behaviour we see," Dr. Townsend told BBC News. "Instead it's explained more by social factors - the absence of a high ranking individual or the absence of a closer affiliate."