What do you call a group of hyenas?

A group of hyenas is called a cackle.

Hyenas are any feliform carnivoran mammals of the family 'Hyaenidae'. With only four extant species (in three genera), it is the fifth-smallest biological family in the 'Carnivora', and one of the smallest in the class 'Mammalia'. Despite their low diversity, hyenas are unique and vital components of most African ecosystems.

Although they are closer to felines and viverrids and belong to the feliform category, hyenas are behaviourally and morphologically similar to canines; both hyenas and canines are non-arboreal hunters that catch prey with their teeth rather than claws. Both of them eat food quickly and may store it, and their calloused feet with large, blunt, nonretractable claws are adapted for running and making sharp turns. However, the hyenas' grooming, scent marking, defecating habits, mating and parental behaviour are consistent with the behaviour of other feliforms.