Introduction

Within the order Rodentia, cooperative or communal nesting and care of young have been reported for 35 species and from 9 of 30 (30%) families. Table 8.1 is based on a review of the literature and lists rodents in which cooperative breeding has been documented. We are not trying to suggest that species can always be discretely classified as cooperative or noncooperative breeders. For example, not all deer mice (Peromyscus maniculatus) breed cooperatively although cooperative breeding has been observed. It may be more useful to envision cooperative breeding as a continuum rather than a unitary phenomenon (Sherman et al. 1995; Lewis & Pusey this volume). At one end of the continuum are groups with more than one reproductively active female. Approximately 57 percent of the 35 species of cooperatively breeding rodents contain more than one breeding female per social group; this system is referred to as “plural breeding”. In groups with plural breeders, all breeding females provide care for young, which typically are reared in a single nest (Brown 1987). At the other end of the continuum of cooperative breeding systems are social groups in which only one female produces offspring and the young that remain at the natal nest typically are reproductively suppressed. These are termed “singular breeders” or are referred to as social systems with “helpers-at-the-nest” (Brown 1987). In the latter type of social system, at least some nonbreeding group members assist in care of the young born to the breeding female.