NEWS AND PERSPECTIVES Measures of food intake in mantled howling monkeys Jose ´ Eduardo Reynoso-Cruz 1,2 • Ariadna Rangel-Negrı ´n 1 • Alejandro Coyohua-Fuentes 1 • Domingo Canales-Espinosa 1 • Pedro Ame ´rico D. Dias 1 Received: 18 November 2015 / Accepted: 10 January 2016 / Published online: 22 January 2016 Ó Japan Monkey Centre and Springer Japan 2016 Abstract Food intake (i.e., the amount of food consumed by an individual) is a crucial measure for studying feeding behavior, but its measurement requires high visibility of individuals and long recording sessions, which are often difficult to accomplish under field conditions. As a conse- quence, studies on the feeding behavior of primates typi- cally do not estimate food intake directly, and focus rather on studying dietary patterns through indirect measures of food intake, such as time spent feeding, number of food bites and food intake rates. The aim of the present study was to determine the validity of these estimators of food intake in mantled howling monkeys (Alouatta palliata) by comparing the estimations with the direct measurement of food intake. We recorded 97 feeding episodes of two male and two female adults, during which we determined the number of ingested food units (i.e., number of leaves and number of fruits), the number of bites taken and time spent feeding. After weighing units of food similar to those consumed, we calculated food intake and mean intake rates per food type (ripe fruits, unripe fruits, mature leaves, and young leaves). The number of bites taken by mantled howling monkeys during feeding episodes was strongly related to food intake, and this relationship was not affected by the type of food ingested. In contrast, neither time spent feeding nor food ingestion rate were related to food intake. These results suggest that the number of bites could be used as a valid proxy to study food intake in this species, whereas the other two measures are likely to yield inaccurate estimates of food intake. Keywords Alouatta Á Bite counts Á Feeding Á Foraging Á Los Tuxtlas Á Time spent feeding Introduction Food intake, a crucial measure for estimating nutrient acquisition through direct observation, is defined as the amount of food in grams consumed by an individual (Zinner 1999; Rothman et al. 2013), and feeding rates, which describe food intake per min (i.e., g/min: Nakagawa 2009), have been used to study the feeding ecology of many primate species (reviewed in Nakagawa 2009). However, in order to obtain reliable estimates of food intake, high visibility of individuals and long recording sessions are required, both of which are difficult under field conditions, especially in the study of arboreal primates. As a consequence, the majority of studies on primate feeding behavior do not estimate food intake, and focus rather on quantifying the time spent feeding on different foods. Variation in physical and chemical properties among food types leads to differences in processing effort (e.g., chewing: Wright et al. 2008; Norconk et al. 2009), which are then reflected in differences in processing time. As a consequence, time spent feeding may not be a reliable measure of the dietary patterns of primate species that consume food types with marked differences in physical or chemical properties, as first noted by Hladik (1977). For instance, in a comparison of the feeding rates for fruits and leaves among six primate species from seven populations, & Pedro Ame ´rico D. Dias paddias@hotmail.com 1 Laboratorio de Ecologı ´a del Comportamiento de Primates, Instituto de Neuroetologı ´a, Universidad Veracruzana, Av. Dr. Luis Castelazo Ayala S/N, Colonia Industrial Animas, 91190 Xalapa, Veracruz, Mexico 2 Present Address: Laboratorio de Adaptacio ´n Animal, Facultad de Psicologı ´a, Universidad Nacional Auto ´noma de Me ´xico, Ciudad de Me ´xico, Mexico 123 Primates (2016) 57:161–166 DOI 10.1007/s10329-016-0513-7