JULY/AUGUST 2019. DISCOVER 45
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Monkeys mainly stick to trees in the
tropics. But not Japanese macaques.
Also known as snow monkeys, the species
endures below-zero temperatures by
growing thick winter coats and huddling
together. One population, in central Japan’s
Jigokudani Monkey Park, hangs out in
104-degree hot springs. The bathing, first
observed in the 1960s, was associated with
reduced levels of stress hormones triggered
by cold, according to a 2018 Primates study.
Love life takes a variety of forms.
Titi monkeys, comprising over 30 species in South America,
are mostly monogamous. Partners stick close together,
often nuzzling and entwining tails, and become distressed
when separated — indicated by calls, agitated movements
and stress hormone levels. While both parents live for years
with their offspring, infant care is predominately dad’s job.
At the other extreme, mandrill monkeys of western
Africa live in hordes of several hundred individuals.
Competition for mates is fierce, and mostly won by the
biggest and brightest: Male snouts, genitals and rumps
are radiant hues of red, blue and purple. Research has
shown that coloration is related to testosterone levels
and dominance. And while these top-ranking males sire
more than 70 percent of offspring, other males sneak
clandestine copulations.
Beyond procreation, some monkeys engage in sexual
acts for pleasure and to strengthen social bonds. At
least 40 species exhibit homosexual behaviors, such
as mounting and genital fondling between same-sex
individuals, which can cause orgasm.
Some wild monkeys use tools.
In Thailand, long-tailed macaques crack open shellfish with
stones (left). On the other side of the globe, in the Brazilian
Amazon, palm nuts are smashed hammer-and-anvil style by
capuchins (right) — clever monkeys boasting the largest brain-
to-body size ratio of any primate besides humans. Regardless
of species, the toolmaking behavior is learned: Young monkeys
spend years mastering the technique, and not all troops partake.
Colorful snouts of
mandrills can be a
clue to dominance.Titi monkeys,
which are
mostly
monogamous,
often sit with
tails entwined.