A her is a large group of animals. The term is usually applied to mammals, particularly ungulates. Other terms are used for similar phenomena in other types of animal. For example, a large group of birds is usually called a flock (this may also refer to certain mammals as well) and a large group of carnivores is usually called a pack. In addition, special collective nouns may be used for particular taxa: for example a flock of geese, if not in flight, is sometimes called a gaggle. However, in theoretical discussions in behavioural ecology, the generic term "herd" is used for all these kinds of assemblage. A herd may also refer to one that tends and cares for such groups (i.e. shepherds tend to sheep, and goatherds tend to goats, etc.).