INFANT-NONMOTHER INTERACTIONS OF FREE-RANGING MANTLED HOWLERS (ALOUATTA-PALLIATA) IN COSTA-RICA

Proximate and ultimate explanations of interactions between infants an d nonmothers vary depending upon the relatedness of the interactors. W e investigated interactions of infants and nonmothers from a 22-month continuous study and from the long-term monitoring of the mantled howl er population of La Pacifica, Guanacaste Province, Costa Rica. Related ness is low or absent in these mantled howler groups. Juvenile females appeared to practice care skills with older infants, but as most firs t infants died, they failed to benefit. Infant positive interactions w ith adults occurred with the mother and probable father Other adult fe males behaved aggressively toward the youngest infants. Mothers were r etentive of infants and responded negatively to these interactions, su ggesting that they perceived them as threatening. Interactions with in fants appear to reflect competition in groups of unrelated adults. A r eview of other populations of Alouatta palliata and other species of h owlers indicate variability in social group size and suggest variabili ty in intragroup relatedness. We suggest that further study will confi rm that social behavior (including interactions with infants) will var y by resource availability (group size) and associated demographic pat terns (male and female migration) that affect relatedness in howler so cial groups.