After two years without any offspring, Basel Zoo’s squirrel monkeys now have a whole troop of new arrivals. Eight tiny monkeys are currently clinging to their mothers’ backs.

These little monkeys with their striking yellow coats were all born at Basel Zoo between 10 May and 17 June.  There is a good reason for the previous lack of offspring: the group was made up entirely of females for two years, until a new male arrived at the zoo at the end of 2019. The recent glut of children was the gratifying result. It has been 34 years since there were this many young squirrel monkeys at the zoo at once.

Of the eleven females in the current group, only the oldest (26) and the two youngest (3) have no young at the moment. The oldest of the three males (13) is the breeding stud and thus the father of the eight babies. 

At Basel Zoo, the squirrel monkeys share an enclosure with the woolly monkeys. The two species get along well: the older squirrel monkey children like to climb all over the woolly monkeys and are sometimes even permitted to ride on their backs.

Males only tolerated during mating season

Squirrel monkeys live in female groups consisting of a mother, her adult daughters and their offspring. Males are expelled from the group at the age of two or three, after which they live in bachelor groups. The strongest bachelors gain huge amounts of weight just before mating season and switch into a female group to produce offspring. Mating season is therefore an exceptional time for this monkey species. At Basel Zoo, this lasts from November to January and the baby monkeys are born five months later. This lines up perfectly with the beginning of insect season, as insects are one of squirrel monkeys’ favourite foods. After mating season, the females will no longer tolerate the presence of males and will drive them away again.

Unlike many primates, squirrel monkeys mark their territory with scent marks and use these as a way to communicate with each other. They do not have special glands for this purpose – they simply urinate over their hands and feet and then rub them into their fur, spreading the scent all over their body and passing it on as they wander around on the branches and ropes. They rub their backs or chests against important parts of the enclosure to pick up the scents of other members of the group or to leave their own scent behind.

Squirrel monkeys can differentiate between the smells of group members and those outside of the group. This ‘urine washing’ becomes particularly vigorous during the mating season.  As a result, squirrel monkeys have their own characteristic smell. The zoo keepers are careful not to clean the climbing structures too thoroughly, to ensure that the scent marks are not removed.

Insect hunting

Squirrel monkeys are also called saimiris. They live in the rainforests of the southeastern Amazon basin, northern Bolivia, southern Peru and eastern Brazil, primarily on riverbanks.  They eat fruit and insects. Around 80% of their time searching for food is spent hunting insects and other small animals. If no fruit is available, they will feed entirely on insects.

Squirrel monkeys are not endangered in the wild, but the population trend is clearly declining. Loss of habitat and hunting are particular issues for this species. A European breeding programme (EEP – EAZA ex-situ programme) coordinates the species’ breeding in zoos, with Basel Zoo serving as the coordinator. The programme covers over 900 animals.