Marine prey processed with stone tools by burmese long‐tailed macaques (Macaca fascicularis aurea) in intertidal habitats

Abstract

Long-tailed macaques (Macaca fascicularis) feed opportunistically in many habitats. The Burmese subspecies (M. f. aurea) inhabits coastal areas in southwestern Thailand and Myanmar, and some of their populations have adapted lithic customs for processing encased foods in intertidal habitats. We investigated the diet of such macaques in Laemson National Park, Thailand, and identified the variety of foods they processed with stones. We conducted 36 shore surveys to study tool sites following feeding activity, during which we counted the minimum number of individual (MNI) food items found at each site. We identified 47 food species (43 animals and four plants), from 37 genera. We counted 1,991 food items during surveys. Nearly all were mollusks (n = 1,924), with the small remainder primarily consisting of crustaceans and nuts. The two most common foods, rock oysters (Saccostrea cucullata; n = 1,062) and nerite snails (Nerita spp.; n = 538), composed 80.2% of our sample. Four prey species comprised 83.2% of the sample (MNI = 1,656), S. cucullata (n = 1,062), Nerita chamaeleon (n = 419), Thais bitubercularis (n = 95), and Monodonta labio (n = 80). Macaques selected a wide variety of foods. However, they heavily concentrated on those that were abundant, easy to access, and sufficiently sized. The Burmese long-tailed macaque stone-processed diet, which focuses on intertidal marine prey, differs from Sapajus and Pan, who use stones primarily for encased nuts and fruits. In terms of diversity of foods exploited, coastal stone-based predation by macaques resembles the diet of coastal-foraging humans (Homo sapiens sapiens).

Long-tailed macaques select mass of stone tools according to food type

“…We have seen from direct observations of macaque tool-use behaviour that a small proportion of macaques have idiosyncratic dependencies on specific tool features and reliably use the same kind of tool. However, our observations also show that a much larger proportion of macaques on Piak Nam Yai use a range of tool sizes, which seem to be in accordance with what we have found in this study (M. D. Gumert 2009Gumert -2012, unpublished data). Additionally, we did not experimentally separate the natural association between size and mass in our study, and thus cannot make conclusions on which of these two physical dimensions the macaques attended to during selection.…”

“…We have determined that 88% of all adolescents and adults living on Piak Nam Yai use stones daily to process foods [33], which amounts to ca 20% of their total activity when on the shore, and 40% of their coastal foraging time budget (M.D. Gumert 2009Gumert -2012, unpublished data).…”

“…12 m long  2.5 m wide). Through these observations, we have acquired a database of their basic activities and general patterns of tool use (M. D. Gumert 2007Gumert -2012, unpublished data). Although we can easily see macaques and can watch them for hours each day, we have difficulty in acquiring information on the details of their tools, foods and behaviour through observation alone, due to the distance, large boulders on the shores affecting visibility, and wave motion affecting the stability of the boat.…”

“…Based on previous findings [31], we predicted that stone mass would vary with the mobility of the food, and that smaller, lighter stones would be more strongly associated with sessile oysters, whereas larger, heavier stones would be associated with motile and detached foods. In addition, given the wide variety of motile prey, as wells as some nuts, being processed by macaques [32], we were able to test how stone tool mass relates to foods in greater detail than in past studies. We expected that stone mass would not only vary based on the mobility, but also with the size and toughness of the food.…”

Archaeological shellfish size and later human evolution in Africa

“…Shellfishing by numerous nonhuman species (14,15), including coastal baboons (Papio spp.) in Africa (16), coastal macaques (Macaca fascicularis) in Thailand (17), and kelp gulls (Larus dominicanus) in South Africa and elsewhere (18), underscore this conclusion. In sum, the nutritional value and easy accessibility of shellfish imply that when coastal occupation sites older than 160-150 ka are found, they will likely reveal yet earlier shellfishing, perhaps from the time that people first occupied sea coasts.…”