Males have bushier antennae than females, which allow them to sense female pheromones for mating. Males usually keep close contact with females in the mating period. Males become more active during mating season. Males often adopt lekking as a strategy to garner females for mating. Males are known to use infrasound during mating bellows. Males are generally solitary, except for mating and fighting. Smaller males may be selected for due to the presence of competition for mating. Sexual preference creates a tendency towards assortative mating or homogamy. These birds are known for remaining in monogamous relationships during the course of mating season. Beavers maintain and defend territories, which are areas for feeding, nesting and mating. Numerous inbreeding avoidance mechanisms operating prior to mating have been described. Butterflies use ultraviolet as a communication system for sex recognition and mating behavior. Larger prey result in longer mating times. Typically, they only come into contact with other moose for mating or competition for mates. The queen cells hatch inside of the mating nuclei.