When I asked Simmons to describe what happens to him when he is with a parrot, he instantly went into one of his signature high-speed soliloquies. ‘‘Here we go,’’ he said. ‘‘Write it down. There are things I have seen that will never leave me. There’s this huge sack of guilt and shame and pain that I carry with me, and I got it when I was 18 years old in Bahrain. Now, when I’m with a parrot, it’s not a total time-change thing, but I do have to act like a 12-year-old boy again. And here’s why. Because parrots are not domesticated animals. They haven’t been bred for hundreds of years to be at my feet.’’ Simmons paused for a sip of Coke, the third one of the night. ‘‘So in order to have a relationship with a parrot, that parrot has to select me. In order for that to happen, that parrot has to be comfortable. I have to come in open and quiet and calm. Much like that 12-year-old boy that met the mean dog next door and never had a problem. Much like that 12-year-old boy that went hiking and saw a mountain lion. I’m acting like the 12-year-old boy again around the parrots, and what that does is help me confront my trauma rather than carry it around. Because now I’m with a psychiatrist, and I’m talking about how this bird didn’t feel so good today and wasn’t very comfortable and was kind of hiding in the back of the cage, and the psychiatrist goes, ‘Hmm, you’re starting to talk about emotions.’ I’m talking about how the bird was feeling, but I’m also transferring my own emotions. So being with the parrots allows me to take that third-person look at my own trauma, which you can never do when you’re whacked out on Vicodin and Budweiser and living under a cement highway bridge.’’

We often think of empathy as a skill rather than the long-ago, neuronally ingrained bioevolutionary tool for survival that it actually is: the ability to inhabit the feelings of fellow beings (the word empathy derives from the Greek en, which means ‘‘in,’’ and pathos, meaning ‘‘suffering’’ or ‘‘experience’’); the ability to feel, for example, their fear over a threat; or thrill over a newly found food source; or sorrow over a loss, which has as much to do with the fabric of a community as any other. Empathy, in this sense, can be thought of as the source of all emotion, the one without which the others would have no register.

The more time I spent at Serenity Park last summer, the more I came to think in terms of the expansive anatomy of empathy. And not just the shared neuronal circuitry that has now been mapped across species, from us to the other primates to elephants and whales and, we now know, to creatures with entirely different, nonmammalian brains, like crows and parrots. I thought, as well, of the extraordinary capacity conferred by that circuitry to recognize and respond to the specific infirmities, both psychic and physical (although those are essentially one and the same) of another species.

I got a sense early on at the park of which parrots and veterans seemed most drawn to one another. The way, for example, Simmons said that the lilac-crowned Amazon, Dagwood, came to life around Jim Minick, the former Navy helicopter crewman. But I learned only later about the true depth of such bonds.