"But we won’t find them among the non-mammals. Their sexual responses are almost certainly more a matter of chemically triggered instinct than pleasure." - And boy are you wrong! I know for a fact that my male cockatoo (a parrot, which is NOT a mammal) masturbates and has orgasms. He wags his tail back and forth as he rubs against something, gripping said object for balance. I can tell when the "moment" arrives, as he leans forward and puts his head down on its side, arches his tail to one side, and completely extends one wing on the same side. Afterwards, the object he has rubbed against is all wet and sticky, and he wants to cuddle. From watching the look on his face, I am sure that cockatoos enjoy the "big O" as much as humans do.