Is Play Sexually Dimorphic in the Polygamous Squirrel Monkey?

Play behavior is widespread in juvenile mammals and may be a mechanism for practicing skills needed in adulthood. In mammals characterized by strong adult male competition over females, juvenile males perform more social play than do females, and such play may assist in later mating competition. This study examined whether social play behavior is sexually dimorphic in a polygamous neotropical primate, the squirrel monkey (Saimiri collinsi), through a six-week field study of two groups of wild monkeys in Eastern Amazonia, Brazil. We hypothesized that males would conduct more rough-and-tumble play than females and that any sex-based play differences would be more evident in older juveniles. We video recorded juvenile play bouts and scored: age category (younger or older juvenile) and sex of players (male or female); and rough-and-tumble play behaviors (i.e., bite, grab, and wrestle). Juvenile males initiated more play bouts than did females. Most players were older juvenile males, while older juvenile females were the least represented. Older juvenile play bouts occurred mostly among males, while younger juvenile bouts consisted of a more even sex distribution. While younger juveniles did not significantly affect the number of rough-and-tumble behaviors in bouts, the number of behaviors was significantly affected by the sex of older individuals. These results indicate that social play is sexually dimorphic in juvenile S. collinsi; specifically, males play more than females and sex differences are more pronounced in older cohorts. KEYWORDS: Squirrel Monkeys; Mating System; Sexual Dimorphism; Juvenile Period; Development; Play Behavior; Social Behavior; Ethology

Marcgrave's red-tailed monkey: the earliest European depiction of a titi monkey

Among the approximately 40 species of mammals described in Historia naturalis Brasiliae by Willem Piso and Georg Marcgrave, the identity of the monkey “cagui major” has been one of the most controversial. Authors have identified Marcgrave's “cagui major” as a tamarin, a saki monkey, a squirrel monkey, a titi monkey and even as an Old-World monkey. Based on a watercolour, probably related to the original illustration that served as basis for the “cagui major” woodcut, we confirm that it depicts a titi monkey ( Callicebus). By comparing the pelage characteristics shown in the drawing and some measurements and pelage characteristics described in Historia naturalis Brasiliae, we confirm that the species depicted was Callicebus melanochir that occurs today in southern Bahia and northeastern Minas Gerais states, outside the range of the Dutch possessions in Brazil.