Grandmothers care for orphans in a provisioned troop of Japanese macaques (Macaca fuscata)

Abstract

This study reports cases in which grandmothers and other closely related adult females cared for orphans in the Arashiyama E-troop, a provisioned troop of Japanese macaques (Macaca fuscata). I observed the behavioral patterns of three orphans (aged 1, 2, and 3 years, respectively). The grandmothers cared for two orphans, while three other closely related adult females cared for the rest of the orphans whose grandmothers were absent. These observations differ from those of previous studies that reported that grandmothers were indifferent towards orphans. This intraspecific variation may be attributed to the demographic conditions of the troop in this study, which had only a few related nulliparous adult females, as a result of artificial birth control. In this group, adult females showed decreased fecundity and an increased interbirth interval as they received birth control treatment; thus, in the absence of their own dependent infants, these females may have invested time in the care of related orphans. Although caregiving by grandmothers is believed to be rare or insignificant in primates, this study suggests that grandmothers and other closely related adult females play an important role for orphans in troops with few related adult females.

A novel methodological approach for group classification during fission of a semi‐free‐ranging group of Japanese macaques (Macaca fuscata)

“…To analyze the degree of kinship across the newly formed groups, we assessed the closest living relative of each individual (Table 2 ). Which individual was regarded as the closest living relative was based on the care providing function during the ontogeny of infants and juveniles in Japanese macaques (MacDonald Pavelka et al, 2002 ; Nakamichi, Onishi et al, 2010 ; Nakamichi & Yamada, 2010 ; Nozaki, 2009 ; Yamada et al, 2005; 2005 ). If the mother of a male was still alive, she would be the closest care‐providing relative and therefore included in this analysis.…”

<NOTE>An Old Female Bonobo Carried a Dead Red-Tailed Monkey for over a Month

“…Allomothering, defined as temporary carrying of non-kin infants is performed mostly by non-parous young females, which has been suggested to be a process of acquiring maternal skills in non-human primates (McKenna 1979). However, it is occasionally conducted by adult parous females without their own infants (Nozaki 2009;Tokuyama 2015). Chio's case fits the latter well, because she had not cared her own infants for a long time.…”

Old grandmothers provide essential care to their young granddaughters in a free-ranging group of Japanese monkeys (Macaca fuscata)

“…Nonhuman primate grandmothers may contribute to the survival of their infant grandchildren (Fairbanks and McGuire 1986;Nozaki 2009). To our knowledge, however, there have been no reported cases in which, instead of a mother, a grandmother without dependent offspring has continuously provided essential care for the survival of her dependent grandchild, which is in accordance with the grandmother hypothesis.…”