A qualitative model on sexual behaviour: mate guarding and extra-pair copulation in birds

Extra-pair paternity is widespread among avian species, showing high inter and intra-specific variation both in frequency and in typical behaviours. These variations are the result of individual, ecological and phylogenetic influences upon the behavioural searching pattern for extra-pair copulations. A qualitative reasoning model was developed to show how decisions made by females and males could affect the occurrence of extra-pair paternity and fitness. The model demonstrates that population density and the genetic quality of the male with whom the female is mated influences female predisposition to search for extra-pair copulations. Accordingly, high-quality males should have a higher number of within and extra-pair young than low quality males. The model shows that since the interests of males and females are similar, both sexes may achieve an increment in their fitness.