Breeding stock is a group of animals used for the purpose of planned breeding. This sets them apart from breeds that are the result of fairly recent selective breeding. Maintaining correct data is important for purebred dog breeding. These changes can improve the chances of mating during breeding season. Little is known about mating behavior, or breeding and birthing areas. Males compete for the opportunity of breeding females. Dispersal may occur in pursuit of feeding opportunities outside of the breeding season. They were described as engaged in cattle breeding. Males exhibit agonistic behavior both on and off breeding and nesting grounds. Genetic variability is essential for progress in breeding. Inbreeding is a technique used in selective breeding. Seabirds use the islands as resting, breeding, and wintering sites. Most migratory butterflies are those that live in semiarid areas where breeding seasons are short. These show cooperative breeding and marked reproductive skews. Making a profit in horse breeding is often difficult.