Using Giving-Up Densities to Test for Dietary Preferences in Primates: An Example with Samango Monkeys ( Cercopithecus (nictitans) mitis erythrarchus)

Abstract

Teasing apart the components of diet selection is important for understanding an animal’s ecology. We used giving-up densities (GUDs) in artificial food patches to test whether free-ranging samango monkeys (Cercopithecus (nictitans) mitis erythrarchus) treat food and water as complementary resources and to examine dietary preferences. To assess the influence of water on the value of food, we measured harvest of peanuts from food patches augmented with water. To examine dietary preferences, we measured the harvest of peanuts (as a standard for comparing other food classes), raisins, alfalfa pellets, and either mealworms or cat food mixed into sawdust in separate food patches. In addition, we observed the samangos’ order of selection of each food. To differentiate preference from ease of encounter, we measured selectivity for peanuts in triplets of food patches containing 1) peanuts, 2) peanuts mixed with a test food (raisins, alfalfa, or mealworms), and 3) the test food. Water did not influence samango foraging. After peanuts, the samangos treated alfalfa and raisins as approximately equal. The samangos foraged on mealworms lightly and rejected cat food. When each food was mixed with peanuts, the monkeys exhibited an expanding specialist dietary strategy in which they altered their rates of encounter with their preferred foods at high resource densities. Samango monkeys at our study site are not water limited, they consistently favor high-energy foods, and they least often choose animal protein. We conclude that patch-use experiments coupled with direct observations provide a useful means for examining dietary strategy, food preferences, and water limitation.