Two ring-tailed lemurs, perhaps a pair, perhaps just two guys out to catch a few rays, sit side by side tilted back as if in beach chairs, their white bellies exposed, knees apart, feet splayed to catch every last drop of the Madagascar sun. All they need are cigars to complete the picture.

There’s a perfectly good evolutionary explanation for this posture. Scientists use the term “behavioral thermoregulation” to describe how an animal maintains a core body temperature. But as the animal behaviorist Jonathan Balcombe points out in his exuberant look at animal pleasure, “The Exultant Ark,” they are also clearly enjoying themselves. A scientist through and through, Dr. Balcombe can’t help giving the study of animal pleasure a properly scientific name: hedonic ethology.

True to its subtitle — “A Pictorial Tour of Animal Pleasure” — “The Exultant Ark” showcases surprising, funny, touching, sad, heartwarming pictures by photographers all over the world. Dr. Balcombe’s text is a serious examination of the subject of animal pleasure, a study that “remains nascent and largely neglected in scientific discourse.” But it also delights us along the way with Dr. Balcombe’s observations and examples.

On the subject of food as pleasure, for instance, he tells us, “Rats will enter a deadly cold room and navigate a maze to retrieve highly palatable food (e.g., shortbread, pâté or Coca-Cola).” If they happen to find rat chow instead, “they quickly return to their cozy nests, where they stay for the remainder of the experiment.”