High population density of black-handed spider monkeys (Ateles geoffroyi) in Costa Rican lowland wet forest

Abstract

The main objective of this study was to estimate the population density and demographic structure of spider monkeys living in wet forest in the vicinity of Sirena Biological Station, Corcovado National Park, Costa Rica. Results of a 14-month line-transect survey showed that spider monkeys of Sirena have one of the highest population densities ever recorded for this genus. Density estimates varied, however, depending on the method chosen to estimate transect width. Data from behavioral monitoring were available to compare density estimates derived from the survey, providing a check of the survey's accuracy. A combination of factors has most probably contributed to the high density of Ateles, including habitat protection within a national park and high diversity of trees of the fig family, Moraceae. Although natural densities of spider monkeys at Sirena are substantially higher than those recorded at most other sites and in previous studies at this site, mean subgroup size and age ratios were similar to those determined in previous studies. Sex ratios were similar to those of other sites with high productivity. Although high densities of preferred fruit trees in the wet, productive forests of Sirena may support a dense population of spider monkeys, other demographic traits recorded at Sirena fall well within the range of values recorded elsewhere for the species.

Diet of spider monkeys (Ateles geoffroyi) in Mesoamerica: current knowledge and future directions

“…Many A. geoffroyi studies have described demographic characteristics of the populations [e.g. DeGama-Blanchet & Fedigan, 2006;Estrada et al, 2004;Milton & Hopkins, 2006;OrtizMartínez & Rico-Gray, 2007;Serio-Silva et al, 2006;Silva-López et al, 2001;Weghorst, 2007].…”

Emergence of sex-segregated behavior and association patterns in juvenile spider monkeys

“…Following Ramos-Fernández (2005), party was defined as a group of individuals which associated with each other and remained within 30 meters of one another. Party sizes were calculated using individually locomoting individuals (ILI), in which dependent infants are not counted as separate individuals (Weghorst, 2007).…”

How Reliable are Density Estimates for Diurnal Primates?

“…However, researchers consider it to be the most reliable and sometimes even view densities calculated from this data to be absolute measures (Brugiere and Fleury 2000). The second, line-transect surveying, is more efficient in terms of both time and finances (NRC 1981), and for this reason is commonly used (Haugaasen and Peres 2005;Rovero et al 2006;Teelen 2007;Weghorst 2007). Researchers must meet several assumptions when using linetransect sampling: no subject on the transect line is missed; subjects do not move before they are detected; subjects are not counted twice; distances and angles are measured accurately; and sightings are independent events (Buckland et al 2001;Ross and Reeve 2003;White and Edwards 2000).…”