Spider monkeys form loose groups of 15-25 individuals. During the day, groups break up into subgroups of 2-8 individuals. This social structure ('fission-fusion') is found in only one other primate species, the Chimpanzee. The size of subgroups and the degree to which they avoid each other during the day depends on food competition and the risk of predation. Also less common in primates, females rather than males disperse at puberty to join new groups. Males tend to stick together for their whole life. Hence males in a group are more likely to be related and have closer bonds than females. The strongest social bonds are formed between females and young offspring.