Complex sentence: The sexes have conspicuously different sizes and sometimes a female will be more than twice as heavy as her mate, sometimes most extreme in specialized bird-eaters, like the "Accipiter" hawks, and borders on non-existent among the vultures.
Split into simpler sentences: The sexes have conspicuously different sizes and sometimes a female is more than twice as heavy as her mate. This sexual dimorphism is sometimes most extreme in specialized bird-eaters, such as the "Accipiter" hawks, and borders on non-existent among the vultures.