Timothy VanZeben, Salt Lake Community College
Ongoing monitoring of primate populations is a useful way of determining the long-term population stability in an environment. Local governments have also been establishing areas of forest into preserves as one way to protect a population of animals. Conservation preserves like these ensure the survival of pristine forests that house animals at risk of extinction. Much of Central America has been reclaiming former pasture lands to grow these preserves. Before my census at La Selva Biological Station there was only one other census of the mantled howler monkey at this location in the literature. The purpose of this census was to determine whether the population was stable in this preserve. I conducted my census of howler monkeys in the Costa Rican province of Heredia in May 2017. My census covered 43.3 kilometers of existing trails which I used as line transects. A distance sampling method was used to determine howler monkey densities. Distance sampling is frequently used to estimate animal densities by measuring animals’ distance from the transect line. These numbers are entered into computer models to return the final density estimates. A geographic information system (GIS) was used to analyze the spatial distribution of animal encounters. Eighty percent of monkeys were found within the secondary forest habitat. In addition to the spatial distribution, this study estimates that there are 10-28 troops and 32-108 howlers/km² in La Selva Biological Station. Computer analysis estimates that I encountered 13 troops during my census time. The lower end of these estimates is within the range found in populations elsewhere in Central America, but more than what was previously estimated for La Selva. Most monkeys were found in secondary forest environments with the highest density located along the Puerto Viejo River. This represents a potentially good sign for land that is being converted back to forest from former plantations. The line-transect method for density estimations is found to not be useful for censusing this area as it is impossible to create random lines.