Material & Methods

This study was carried out using five adult white-faced sakis held at Furuvik Zoo, Gävle, Sweden.

Food preferences were assessed using a two-alternative choice test. Each animal was presented with pairs of equally-sized food items, and its choice behavior, i.e. which of the two food items was consumed, was recorded.

In each test session the animals voluntarily entered the testing cage and placed themselves on a wooden platform attached to a metallic mesh that separated the testing cage from the enclosure’s service area.

The 15 different types of food employed were broccoli (Brassica oleracea var botrytis), cucumber (Cucumis sativus), tomato (Lycopersicum esculentum), carrot (Daucus carota), eggplant (Solanum melongena), beetroot (Beta vulgaris), sweet potato (Ipomoea batatas), avocado (Persea americana), Napa cabbage (Brassica rapa, subsp. pekinensis), apple (Malus pumila), peanut (Arachis hypogaea), honey melon (Cucumis melo), hazelnut (Corylus avellana), mealworms (i.e. larvae of the mealworm beetle Tenebrio molitor), and hard-boiled egg (from chicken, Gallus gallus). Food items are presented in the previous order, from left to right:

All foods were cut to (or presented at) an equal size, approximating cubes with a side length of 2 cm to avoid choice behavior being affected by size differences.

The food was presented on a cutting board and was covered by a box until its front edge came in contact with the mesh at the height of the wooden platform in order to guarantee that the sakis would be exposed to both food items simultaneously. The mesh was wide enough to allow the sakis to fit their hand through and grab hold of the food items.  

A total of 5250 choices were recorded, which correspond to the 105 possible binary combinations of the 15 food items presented 10 times to each of the 5 animals. For each food pair presented to the sakis, 1 point was attributed to the food item eaten, whilst the remaining food item was attributed 0. Alternatively, 0.5 points were attributed to both food items when the sakis failed to choose within 10 seconds from the removal of the box covering the food items.

Food preference rankings were established both at the individual and at the group level and tested for statistical significance using the two-tailed binomial test. Spearman rank-order correlations were evaluated between the food preference rankings and the contents of macro- and micronutrients.