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Detecting and identifying predators quickly is key to survival. According to the Snake Detection Theory (SDT), snakes have been a substantive threat to primates for millions of years, so that dedicated visual skills were tuned to detect snakes in early primates. Past experiments confronted the SDT by measuring how fast primate subjects detected snake pictures among non-dangerous distractors (e.g., flowers), but did not include pictures of primates' other predators, such as carnivorans, raptors, and crocodilians. Here, we examined the detection abilities of N = 19 Tonkean macaques (Macaca tonkeana) and N = 6 rhesus macaques (Macaca mulatta) to spot different predators. By implementing an oddity task protocol, we recorded success rates and reaction times to locate a deviant picture among four pictures over more than 400,000 test trials. Pictures depicted a predator, a non-predator animal, or a simple geometric shape. The first task consisted of detecting a deviant picture among identical distractor pictures (discrimination) and the second task was designed to evaluate detection abilities of a deviant picture among different distractor pictures (categorization). The macaques detected pictures of geometric shapes better and faster than pictures of animals, and were better and faster at discriminating than categorizing. The macaques did not detect snakes better or faster than other animal categories. Overall, these results suggest that pictures of snakes do not capture visual attention more than other predators, questioning previous findings in favor of the SDT. [ABSTRACT FROM AUTHOR]

Abundant empirical and theoretical studies indicate that predation is a key driver of primate evolution. The Snake Detection Theory (SDT) posits that snakes have been the main predators of primates since the late Cretaceous and that they influenced the diversification and evolution of primates. Laboratory research focusing on the innate ability of primates to detect snakes amid complex visual stimuli has provided strong support for key tenets of the SDT. While this theory has greatly contributed to our knowledge of primate evolution, supporting experimental studies may have overly focused on snakes and disregarded other important predators. This potential sampling bias weakens the conclusion that primates respond with a specific (high) intensity to snakes compared to other predators. We reviewed the literature about primate-predator interactions under natural and experimental conditions. We listed the primate and predator species involved in natural versus experimental studies. Predation events on primates recorded in the field mainly involved other primates, then raptors and carnivorans. SDT-related experimental studies heavily focused on snakes as predator stimuli and did not include raptors. Other experimental studies largely used snakes and primates and to a lesser extent carnivorans. Apes were the most often tested primates in experimental studies, whereas other primate taxa were neglected. Moreover, predators used as stimuli in experimental studies were inaccurately identified, notably snakes. Altogether, our results show that SDT-related studies neglected most of the major natural predators of primates. SDT studies also focused on a handful of primate species, whereas the theory relies on comparisons among taxa. Finally, poor taxonomic information on snakes used as stimuli blurs the interpretation of their relationship with primates. We suggest that future studies test the SDT by presenting a wide range of predators to different primate species to improve our understanding of the complexity of predator–prey interactions. [ABSTRACT FROM AUTHOR]

Examines the behavioral evidence for visual recognition of predators by the mangrove climbing crab Sesarma leptosoma in Malindi, Kenya. Orientation of the crab on a three-dimensional habitat; Use of dummy objects for detecting dangers such as predators; Ability of the crab to perceive shape and distinguish motionless objects.