Gerry Carter studies cooperative relationships in vampire bats with the larger goal of understanding the biology of social bond formation. How do strangers become friends? When two unfamiliar female vampire bats form a new social bond, it involves natural, frequent, and costly helping behaviors that Carter can monitor, measure, and manipulate over time. His goal is to use lab experiments and field observations to test theory-based predictions about the ecological forces, biological mechanisms, and cognitive strategies that might shape how individuals create and maintain cooperative relationships. He hopes to gain fundamental insights applicable to other socially complex mammals.