Tuesday, June 15, 2010

Bring a Baby

Barbary macaques (Macaca sylvanus) are indigenous to the mid- and high- altitude (1200-2000m) oak, cedar, and scrub forests of Northern Africa mainly in Algeria, Tunisia, Morocco and the Gibraltar peninsula. They are large primates that have silky grey-brown to grey-yellow coats, dark pink faces, and lack a tail. They live in territorial ranges in troops ranging in size from 7 to 40 individuals (usually around 30). They are omnivores that subsist on a diet of tubers, fruits, leaves, rhizomes, seeds, invertebrates, and flowers.

They have a promiscuous mating system in which females mate with all the male members of the group. Females typically remain within their natal groups while males often disperse from these groups. This dispersal behavior in the males is critical for gene flow and the reproductive success of individual males. Every 2 years a female will give birth to a single offspring after a 165 day gestation period, and then the infants will cling to their mothers starting immediately after birth. These young primates are well-developed and will stay and nurse from their mothers for about a year. Male macaques are known to tend to a single young macaque, grooming protecting, and playing with the youngster. After all, with this type of mating system any male could potentially be the father of an infant, so it benefits a male to care for young. Males will establish hierarchies, hierarchies that change with the age of the males and the males that leave or enter the troop.

A new paper in Animal Behaviour describes how male Barbary macaques use infants as “costly social tools.” The researchers noticed that after an infant was born a male would slowly approach the mother and then seize the infant. The infant-toting male would then approach other males in the group, and non-infant-toting males would not interact. The males would hold infants for hours at a time, occasionally taking them back to their mothers for feedings. By using behavioral observations, social network analysis, and measures of fecal glucocorticoid metabolites (indicator of physiological stress) and comparing these to various seasons (spring birth season and autumn season) the authors were able to tease apart some of these male social behaviors. The hypothesis was that the infants would calm the males. However, analysis of hormone levels showed that stress hormones increased, suggesting that the males carried the infants to show that they could handle the pressure. Social network analysis showed that those males who carried infants was not related to rank, and that infant-carriers had stronger ties with other males when compared with non-infant-carriers.

Who knew that males macaques were such suckers for babies? I guess those furry, pink, wrinkly faces are kinda cute.

Here's the paper:
Henkela, Stefanie, Michael Heistermannb and Julia Fischer (2010) Infants as costly social tools in male Barbary macaque networks. Animal Behaviour: 79 (6), 1199-1204. (DOI: 10.1016/j.anbehav.2010.02.005)
and here's a great article in The New York Times:
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