International Journal of Primatology, Vol. 24, No. 5, October 2003 ( C  2003) Population Reduction and Social Disorganization in Alouatta pigra Following a Hurricane Mary S. M. Pavelka, 1,2 Olivia T. Brusselers, 1 Dana Nowak, 1 and Alison M. Behie 1 Received July 24, 2002; revised November 27, 2002; accepted January 15, 2003 The opportunity to study the effects of a powerful hurricane on monkey popu- lations, diet, and behavior via pre- and post-hurricane data was presented when hurricane Iris virtually destroyed the forest along Monkey River in southern Belize on October 8, 2001, including a 52-ha area where black howlers have been subjects since 1999. Before the hurricane, 8 social groups, averaging 6.37 members, had been stable in both group composition and range for ≥ 2 years. The hurricane, which levelled much of the forest, resulted in the complete loss of the forest canopy. The trees that remained standing lost most or all branches and were 100% defoliated. The monkey population in the study area was reduced by 42% and survivers experienced a period of extended so- cial disorganization involving transient individuals, high numbers of solitary monkeys, and small fragmentary social groups. The period of disorganization lasted 12 weeks, after which the number of solitaries reduced and stability of the large groups increased. Within the study area, 5 social groups have been more or less stable since ca. week 15; however, home ranges had yet to stabi- lize at week 35. The social and ranging effects are similar to what has been described for translocated primates. Post-hurricane diet was limited to fruit and leaves remaining in the deadfall for the first 2 weeks and to new leaves and leaf buds for many weeks after that. Normal fruit consumption in April and May was prevented by the failure of surviving trees to produce fruit. With the loss of forest canopy there has been increased use of low foliage and ground 1 Department of Anthropology, University of Calgary, 2500 University Drive N. W., Calgary, Alberta, Canada T2N 1N4. 2 To Whom Correspondence should be addressed; e-mail: pavelka@ucalgary.ca. 1037 0164-0291/03/1000-1037/0 C  2003 Plenum Publishing Corporation