Cooperative breeding
Kenya, 1975-1985
Charles Darwin struggled to explain the evolution of co-operation and apparent altruism (e.g. in social insects). Such behaviour for the benefit of others seemed to contradict his theory that natural selection produces organisms that maximise their own fitness. Today we know of various ways in which cooperative behaviour can evolve – sometimes even within the same species, as my studies of the African Pied Kingfishers (Ceryle rudis) in Kenya have shown.
Males that remained unpaired due to a heavily skewed sex ratio helped breeding pairs to rear their young. Primary helpers increased their indirect genetic fitness trough improving the survival of younger siblings; secondary helpers boosted their direct genetic fitness by enhancing their own future reproductive prospects. Breeding pairs tolerated primary helpers (their offspring from previous years) under all environmental conditions. Unrelated secondary helpers, on the other hand, who competed with the males for the few females, were tolerated only under the poor food conditions of Lake Victoria, where additional help was needed for successful chick-rearing. Under the good food conditions of Lake Naivasha, secondary helpers were driven away by the breeding males. The relative importance of direct and indirect fitness for helper behaviour therefore varies with ecological conditions.
