A case of co‐operative nursing and offspring care by mother and daughter feral horses

Among mammals, non‐offspring nursing is the most extreme form of communal parenting. This is because lactation is the most energetically costly part of parental investment (Clutton‐Brock, 1991; Packer, Lewis & Pusey, 1992). Non‐offspring nursing is most common in species characterized by large litters and small kin groups (Packer et al ., 1992; e.g. lions Panthera leo : Pusey & Packer, 1994). Although non‐offspring nursing has also been reported in monotocous species (e.g. water buffalo Bubalus bubalus , Murphey et al ., 1995; African elephant Loxodonta africana : Dublin, 1983; Lee, 1987; Indian elephant Elaphus maximus : MacKay, 1973; Rapaport & Haight, 1987; fallow deer Cervus dama : San José & Braza, 1993) it is almost always associated with reproductive errors (Riedman, 1982) such as milk theft or exclusive adoption (Packer et al ., 1992). However, simultaneous non‐offspring nursing in monotocous species has been reported in some bat species (e.g. McCracken, 1984; Eales, Bullock & Slater, 1988), African elephants (Lee, 1987), and captive Indian elephants (Rapaport & Haight, 1987). Recent research, however, suggests that nutritive non‐offspring nursing in African elephants is rarer than previously thought as most reported instances were probably non‐lactating juveniles allowing infants to suckle (Lee & Moss, 1986; Lee, 1987, 1989).