Relative Brain Size within the North American Sciuridae

Abstract

Statistical associations were sought between relative brain size and arboreality, diet, habitat, sociality, and reproductive effort among 33 species of North American sciurids. When using all 33 species, arboreality (species classified as arboreal or terrestrial) was found to be a better predictor of brain size compared to diet (folivore or other) or habitat (grassland or other). Arboreal squirrels had significantly larger brains for their body size than did terrestrial squirrels. No relationship was found between relative brain size and reproductive effort. Within the terrestrial squirrels, no relationships were found between brain size and diet, habitat, or sociality (social or asocial). Although these analyses showed that arboreal squirrels had larger brains than did terrestrial squirrels, it is not clear whether this difference is due to (1) selection for large brains in arboreal species, or (2) small brains in terrestrial squirrels as a result of selection for rapid growth rates of young.