Male wants the bigger tympanum so they can hear other bullfrogs and make their voices deeper. Birds produce sounds but they don"t have a vocal box. Song has two main functions is 1) advertising ownership of territory other males. For most one song does both of these things, but other birds especially tiny colorful evolution of song. Females will choose the males on the quality of their song so female choice is driving the. Female choice is a major part of sexual selection and a driving force in evolution. Alaska different breeding system where the bulls call the cows. During the rut cow moose call to attract bulls. Bulls also vocalize and make non vocal sounds by thrashing with their antlers especially at day break on branches. Advantage to producing sound don"t need to be seen. Multiple partners can hear the sounds transmits widely.