I never understood why people say that humans are one of the few "animals" that have sex for pleasure. All animals have sex for pleasure. You think dogs have sex for the purpose of reproduction? They do it to relieve their natural urges -- because it feels good.
That's true of male animals. Male animals always want sex, but they check to see if the female is in heat or not. In most animals, they either won't have sex or the female wont let them have sex if she's not in heat. "Sex for pleasure" means that the females allow the males to have sex with them even when they aren't fertile. This is true only of humans and dolphins.