In his classic essay “What Is It Like to Be a Bat?” the philosopher Thomas Nagel attempts to enter the pteropine mind. Bats, he notes, spend a lot of their time dangling upside down. At night, they swoop around, searching for bugs and issuing high-pitched chirps that allow them to navigate in the dark. A person can imagine what it’s like to hang by his toes from a rafter. He may also be able to envisage having webbed arms, and maneuvering via echolocation, and catching insects on the fly. From this, he can get a sense of what it would be like for him to behave like a bat. But still he would not know what it’s like to be a bat. Even in his wildest dreams, a person has access only to the resources of the human mind, and here, according to Nagel, lies the rub: “Those resources are inadequate to the task.”

Nagel’s essay first appeared in 1974, in the journal The Philosophical Review. It could just as well have been titled “What Is It Like to Be an Aardvark?” or “What Is It Like to Be a Zebra?” The gap separating humans from bats is much the same as—or at least of a similar magnitude to—that which separates us from sloths and pangolins and manatees and meerkats. Like us, these animals are mammals, and we concede that they are capable of some sort of subjective experience. (“Too far down the phylogenetic tree,” Nagel observes, and “people gradually shed their faith that there is experience there at all.”)

Though Nagel wasn’t much interested in other species—his real subject was the irreducibility of consciousness—to those who were, his question became a kind of taunt, an elbow thrust across academic disciplines. Even naturalists who considered the premise of his argument to be misguided felt obliged to address it. In 2012, for instance, a British zoologist named Tim Birkhead wrote a book on avian perception. In his introduction, Birkhead called Nagel’s point “subtle and pedantic perhaps, but that’s philosophers for you.” Birkhead provocatively subtitled his book “What It’s Like to Be a Bird.”

Into this much-contested territory trots Charles Foster, author of…