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 term `` herd '' is used for all these kinds of assemblage . Special collective nouns may be used for particular taxa ( for example a flock of geese , if not in flight , is sometimes called a gaggle ) but for theoretical discussions of behavioural ecology , the generic term herd can be used for all such kinds of assemblage .