Friederike Range of the Messerli Research Institute at the University of Veterinary Medicine in Vienna and colleagues at Austria's Wolf Science Center are the first to document the emotional context of wolf howling in the Aug. 22, 2013, issue of the journal Current Biology.
The researchers determined that position of dominance in the pack – an indicator of the strength of relationships – is the primary factor that produces howling behavior when an animal leaves the pack.
The practice at the Wolf Science Center is for individual trainers to take each wolf for a walk separate from the pack. The walks produce a howling response from the animals left behind.
The researchers documented the social rank of each member of the pack and tested each member for blood levels of the stress hormone cortisol after individual members were taken for a walk for a long period of time.
The length of and extent of howling behavior corresponded to social relationships. The levels of stress did not change based on cortisol testing.
The researchers propose a relationship basis for the duration of howling and the extent of howling that may indicate a signaling to missing members of a pack to return to the group. The duration of the howling behavior is determined by the rank in the pack of the individual wolf.
The behavior could be considered as an emotional response to the departure of a friend in human terms.