Pack Structure and Communication

African wild dog packs are typically dominated by a single monogamous breeding pair. The alpha female typically has a litter of 2 to 20 pups, which are cared for by the entire pack (cooperative breeding). This is the only breeding pair of dogs in the pack. The entire pack is involved in the welfare of the pups; the hunting members regurgitate meat for the nursing female and pups. The dogs are highly social, and share food and provide assistance to weak/sick members. 

Social interactions are common, and the dogs communicate by touch, actions, and vocalizations.

Their large range of vocalizations includes a short bark of alarm, a rallying howl and a bell-like contact call that can be heard over long distances. Elaborate greeting rituals are accompanied by twittering and whining. The dogs constantly maintain physical contact or relatively short inter-individual distances while resting. Unlike wolves, they typically disperse in groups. Lone dogs and peripheral pack members are rare. Compared to wolves, aggression is generally muted; additionally the dogs do not howl. Cooperation is the key to survival and reproduction.

 The vocal repertoire of the African wild dog is one of the most complex in Canidae, with some sounds unique to the species. Vocalizations provide a useful window on larger patterns of behavior, particularly among the dogs. Short-range vocal communication accompanies many social interactions and appears to play an important role in intra- and interpack dynamics, and in forming and maintaining social bonds between pack members. Depending upon the motivational state and level of arousal of pack members, sounds issued by individuals can give rise to cascading group effects.

When filtering through bush in search of prey, pack members frequently become separated and sometimes call to reunite. Long distance contact calls are common in packs and assume the form of pulsed trains. These sounds known as "hoos" are low-pitched and short, and given in bouts of varying length and intensity. They are delivered with the head held slightly lower than the shoulders, a gaping mouth, and often on the run.

http://www.arkive.org/african-wild-dog/lycaon-pictus/video-08d.html
http://www.awdconservancy.org/natural%20history.html
http://www.bbc.co.uk/nature/life/African_Wild_Dog#p00f8633
http://animals.nationalgeographic.com/animals/mammals/african-hunting-dog/