Howling and other vocalisations

Howling adult wolf at the UK Wolf Conservation Trust

Wolf howls, which can last from 0.5–11 seconds, typically have a frequency of 150-780 Hz.[17] Howling helps pack members keep in touch, allowing them to communicate effectively in thickly forested areas or over great distances. Howling also helps to call pack members to a specific location. Howling can also serve as a declaration of territory, as shown in a dominant wolf's tendency to respond to a human imitation of a "rival" wolf in an area the wolf considers its own. This behavior is stimulated when a pack has something to protect, such as a fresh kill. As a rule of thumb, large packs will more readily draw attention to themselves than will smaller packs. Adjacent packs may respond to each others' howls, which can mean trouble for the smaller of the two. Wolves therefore tend to howl with great care.[102] Wolves will also howl for communal reasons. Some scientists speculate that such group sessions strengthen the wolves' social bonds and camaraderie—similar to community singing among humans.[102] During such choral sessions, wolves will howl at different tones and varying pitches, making it difficult to estimate the number of wolves involved. This confusion of numbers makes a listening rival pack wary of what action to take. For example, confrontation could be disastrous if the rival pack gravely underestimates the howling pack's numbers. A wolf's howl may be heard from up to ten miles (16 km) away, depending on weather conditions. Observations of wolf packs suggest that howling occurs most often during the twilight hours, preceding the adults' departure to the hunt and following their return. Studies also show that wolves howl more frequently during the breeding season and subsequent rearing process.[103] The pups themselves begin howling soon after emerging from their dens and can be provoked into howling sessions easily over the following two months. Such indiscriminate howling usually is intended for communication, and does not harm the wolf so early in its life.[102] Howling becomes less indiscriminate as wolves learn to distinguish howling pack members from rival wolves. The Arabian and Iranian wolf subspecies are unusual as they are not known to howl.[6][104]
Growling, while teeth are bared, is the most visual warning wolves use. Wolf growls have a distinct, deep, bass-like quality which can range from 250-1,500 Hz.[17] It is often used to threaten rivals, though not necessarily to defend themselves. Wolves also growl at other wolves while being aggressively dominant. Wolves bark when nervous or when alerting other wolves of danger but do so very discreetly and will not generally bark loudly or repeatedly as dogs do. Instead they use a low-key, breathy "whuf" sound which can measure from 320–904 Hz[17] to immediately get attention from other wolves. Wolves also "bark-howl" by adding a brief howl to the end of a bark. Wolves bark-howl for the same reasons they normally bark. Generally, pups bark and bark-howl much more frequently than adults, using these vocalizations to cry for attention, care, or food. A lesser known sound is the rally. Wolves will gather as a group and, amidst much tail-wagging and muzzle licking, emit a high-pitched wailing noise interspersed with something similar to (but not the same as) a bark. Rallying is often a display of submission to an alpha by the other wolves.[105] Wolves also whimper, a sound with a maximum range of 3,500 Hz,[17] usually when submitting to other wolves. Wolf pups whimper when they need a reassurance of security from their parents or other wolves.