Reciprocal food sharing

Reciprocal food sharing is a form of reciprocal altruism in which an individual animal gives up the food it has foraged to another individual. Food sharing has been observed in a wide range of animals, including insects, birds, cetaceans, vampire bats, and primates. It is not always an active behavior; tolerance of theft may also be considered a form of food sharing (Stevens and Gilby). Not only does food sharing occur among members of the same family, but also among non-kin individuals as well, creating an interesting evolutionary question.

Vampire bats

Vampire bats, which primarily feed on livestock or other vertebrates, must obtain a meal every 48–72 hours or face starvation. On a given night, there are individuals that do not successfully feed. Fortunately for them, a successful individual may regurgitate their meal for the unsuccessful individual. For this trait to persist through evolution, a level of recognition is necessary among individuals. An altruistic bat may refuse to regurgitate blood for another bat that has not given blood to others in the past. The mechanism for this reaction is unknown.

Food for non-food repayment

Grooming

Wilkinson suggests that repayment of blood-giving may not necessarily be in the form of blood, but perhaps grooming.

Meat-for-sex hypothesis

Males of a certain insect, bird, or mammal species may give food to a female to increase their own reproductive success. The food provision may occur before copulation to attract females, or after copulation to nourish the female and increase her fecundity. Among some cannibalistic insect species, the male may provide food to the female to prevent her from eating him after copulation.