"Symington (1987) reported that...infant males were carried longer than infant females; and there was a longer interval between the initiation of nursing and attempts by the mother to reject nursing. Although most offspring are weaned by age two years...a male was observed nursing as late as 31 months. She observed no gender-based difference in post-weaning investment, with juveniles of both sexes traveling and sleeping with their mothers for the first four years..." (Spider Monkeys; Behavior, Ecology and Evolution of the Genus Ateles, ed by Christina J. Campbell, 2008.)
Because spider monkeys are frugivores, a soy infant formula is a more biologically appropriate substitute for mother's milk than one made from cow's milk. This was particularly obvious when we initially switched Lolita from 2% milk to the Isomil soy formula, and watched her poop transform from floating white chunks to tootsie rolls.
Chiquito has gained two pounds since we weighed him for the first time in mid-February, and is now 12 lbs 2 oz.