Revisiting the fourth dimension of tool use: how objects become tools for capuchin monkeys

Dogs functionally respond to and use emotional information from human expressions

Emotions are critical for humans, not only feeling and expressing them, but also reading the emotional expressions of others. For a long time, this ability was thought to be exclusive to people; however, there is now evidence that other animals also rely on emotion perception to guide their behaviour and to adjust their actions in such way as to guarantee success in their social groups. This is the case for domestic dogs, who have tremendously complex abilities to perceive the emotional expressions not only of their conspecifics but also of human beings. In this paper we discuss dogs' capacities to read human emotions. More than perception, though, are dogs able to use this emotional information in a functional way? Does reading emotional expressions allow them to live functional social lives? Dogs can respond functionally to emotional expressions and can use the emotional information they obtain from others during problem-solving, that is, acquiring information from faces and body postures allows them to make decisions. Here, we tackle questions related to the abilities of responding to and using emotional information from human expressions in a functional way and discuss how far dogs can go when reading our emotions.

Stone tools differences across three capuchin monkey populations: food's physical properties, ecology, and culture

Robust capuchin monkeys (Sapajus) are known for processing mechanically challenging foods, having morphological adaptations to do so. However, several populations go beyond body limitations by using stone tools to expand their food range. Those populations use stones in a variety of ways, goals, and with different frequencies. Stone tool size correlates with the food's resistance within some populations. However, we have no detailed comparisons to identify if this correlation is the same across populations. This study described and compared stone raw material availability, food's physical properties (hardness and elasticity), and stone tool weight in three populations of bearded capuchin monkeys (Sapajus libidinosus), including a newly described site (Chapada dos Veadeiros National Park, CVNP). The differences we observed regarding stone tool weight selection among sites were not correlated to the food's physical properties we analyzed. Lithic resource availability could partly explain some differences in the stone tools used. However, the tool weight differences are larger than the raw material variance across sites, meaning some distinctions are possible behavioral traditions, such as the same fruit (Hymenaea) being processed with bigger than needed tools in CVNP than in the other two sites. Capuchin monkey behavioral variability in stone tool use can be caused by several interacting factors, from ecological to cultural.