Hand and mouth use during food acquisition under naturalistic
conditions
We characterized encounter with packaged food and urbanization for 25
videos of bonnet macaque (BM), 5 videos of Japanese macaque (JM) and 10
videos of vervet monkey (VM) which resulted in 174, 282 and 130
instances of FA and FP, respectively. As a result of paucity of video
records, all categories of encountering packaged food and urbanization
were not adequately obtained for all taxa. Classification of food items
considered in the analyses and their relative representation is shown in
Figure S1. In addition, comparison of hand/mouth use in FA between
urbanization conditions with regard to individual food type show higher
hand use in more urbanized groups than less urbanized groups (BM: fruit;
JM-leaf and seed; Fig. S1), except for processed food in BM where hand
use was equivalent between moderately urbanized and highly urbanized
groups.
Inter-rater agreement based on a two-way random effects model (ICC(2,2),
see Koo & Li, 2016) was over 0.86 (N=50) for each variable (age,
foraging, attached, embedded and anatomical manipulator). We found near
identical pattern of hand use during FA in every primate species we
analyzed, i.e., higher hand use on higher encounter with packaged food
and higher degree of urbanization. The dataset in bonnet macaques (BM)
was devoid of any record of mouth use in the High categories of
encounter with packaged food and urbanization and had the following
trend in mouth use across both these variables, encounter with packaged
food - High (P=0/75) < Moderate (P=18/73) and degree of
urbanization - High (P=0/46) < Moderate (P=18/98) (Fig. 2).
The illustration of Pearson’s standardized residuals for bonnet monkeys
in Figure 2 affirms the hand/mouth bias across High and Moderate
categories in encounter of packaged food and urbanization. Assessment of
FA in the Japanese monkey (JM) and vervet monkey (VM) showed a similar
trend across encounter of packaged food (JM: High (P=0/93) <
Moderate (P=15/51) < Low (P=73/127), Cohen’sd Moderate-Low=0.508; VM: High (P=4/49)
< Low (PL=11/33), Cohen’sd High-Low=0.527) and urbanization (JM: Moderate
(P=15/144) < Low (P=73/127); VM: Moderate (P=4/50) <
Low (PL=11/33)) (Fig. S2 and Fig. 2). The alternate
statistical approach, which modeled FA in the vervet monkey as a
negative binomial distribution within a binary logistic regression did
not find any influence of age, foraging style, food attachment and food
embeddedness but extent of encounter with packaged food (Log
likelihood(N=82)=-34.9; FA: Mouth (ref. ); Encounter with packaged
food: High (ref. ); βLow=-1.727±0.639SE, p=0.007;
Table S1). The probability of FA using hands by vervet monkeys of the
low encounter category decreased by a factor of 0.18 relative to vervet
monkeys in the high encounter category (Table S1). Because the
covariates of FA, extent of encounter with packaged foods and
urbanization were correlated (Contingency coefficient=0.71), only one of
the variables was used in the model.
Processing of embedded food typically involved peeling
fruits/flowers/nuts and removing inedible portions of fruits/leaves,
while extraction involved tearing garbage bags using hands, mouth or
both (hand-mouth) in tandem. The use of hand during hand-mouth assisted
extraction/processing also included situations where the hand has a
passive role of supporting food as well as ones where the hand is
actively involved in orienting/manipulating food (e.g., grabbing by hand
while tearing with mouth) while in the mouth. Due to low sample sizes
(NBM=20, NJM=11, NVM=47)
and insubstantial statistical representation across encounter with
packaged food and urbanization, we could not analyze hand/mouth use
during food extraction by any species.