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The aim of this study is to evaluate long-term demographic variation in ursine howler monkeys (Alouatta actoidea). Demographic information was obtained from published data of a population of ursine howler monkeys of 15 to 36 groups inhabiting the Venezuelan llanos between 1970 and 1999 (Rudran & Duque-Fernández, 2003. Int. J. Prim. 24: 925-947). This dataset was used because it provided detailed records to model projections of demographic changes in atelines. Exponential projections, ordinary least-square linear trend lines, Leslie’s matrix projections, net reproductive rate (R0), and the intrinsic rate of population increase (r) were calculated for these established social groups. Over the course of three decades, this population appeared to be relatively stable. However, although the net reproduction (R0 = <1) and the intrinsic rate of population (r = <0) increased, the population was stable over 30 years, even though there was evidence of periods of marked fluctuations in the number of individuals. Overall, the rate of population growth is likely the result of stochastic processes including drastic environmental events such as El Niño (ENSO) years. Therefore, the ability of Alouatta to cope with major short-term and marked changes in their environment is likely to have a significant evolutionary effect on life history patterns of this primate group. In addition, this study serves as an example to understand the potential impact of climate change on primate populations.