Pup rearing: the role of mothers and allomothers in free-ranging domestic dogs.
Allomaternal care (AMC) is provided to the offspring by individuals other than the genetic mother, including several seemingly altruistic behaviors such as babysitting, carrying, nursing, crèching, or huddling for thermoregulation. To determine whether there is any allomaternal care among free-ranging domestic dogs, from March 2015 to May 2019 a total of eight dog groups consisting of 19 adult females (range 2-3 females per group) that were matrilineal relatives, i.e., maternal grandmothers, aunts, daughters, sisters were observed during pup-rearing period (1st to 13 weeks of pups' life). During the first two weeks, lactating bitches were observed to spend the most time with their own pups and suckled for almost the entire observation period (30 min). Lactating mothers started to venture out of their dens for short foraging trips when the pups were 1 week old, but it was more frequent at 3 weeks of age. From the 3rd week of kin-related pups' life the lactating mothers were observed to wean, with a parallel shift of nursing and regurgitation for the pups done by other kin-related females showing the evidence of allonursing. The occurrence of all types of nursing activities i.e., duration of contact, nursing, feeding by regurgitation, and protection of pups was higher among the mothers than among the allomothers. In the case of biological mothers, the frequency and duration of contact, nursing and feeding by regurgitation decreased as the puppies aged, meanwhile in the case of allomothers, the frequency and duration of contact, nursing and feeding by regurgitation increased until 6 weeks of age, before switching to a decreasing trend. Allonursing in free-ranging domestic dogs was more common among older bitches i.e., maternal grandmothers. We propose four possible reasons of allonursing in the case of free-ranging dogs- (1) having excess milk perhaps due to high pup mortality allonursing may evolve as low cost behavior in free-ranging dogs, (2) allonursing may provide substantial benefits to pups regarding growth, survival, and the transfer of immune compounds, (3) insufficiency of own mother's milk may be one of the causes of allonursing, and (4) free-ranging domestic dogs nurse each other's pups perhaps to promote a set of affiliating and permissive relationships among the group members. As the studied groups contained matrilineal related female dogs that helped each other with allonursing, this study strongly suggests the kin selection theory especially as allonursing is highly prevalent in other, closely related, gregarious wild canids (gray wolves, golden jackals).