After 39 years of service David S. Kessler, the longest serving keeper at the National Zoo in Washington, is leaving. (Gabe Silverman/The Washington Post)

On his last night as the longest-serving keeper at the National Zoo, David S. Kessler checks and rechecks the locks on the enclosures in the Small Mammal House. He collects his farewell gifts and mementos and softly narrates to himself what needs to be done. “Okay, lights out here, good. Hi, babies!” he says to Reuben and Jolla, the howler monkey couple. “Aagh, g’night, sweetheart. Did I wake you up? I’m sorry.” He checks the seven timers on the lights, saying “timer” aloud at each. He’s not thinking, he says, about how this January night is the last time after 39 years, two-thirds of his life, at the zoo. Now Gus the rock hyrax — who looks like a four-pound guinea pig but is more closely related to the elephant — catches his attention in the dark. It’s as if the little guy knows something is up.

Considering the personal magnitude of the occasion, everything is going fine as Kessler prepares to walk away from the animals who he says rescued him, who might just have saved his sanity. “Gus is sticking his head out — ” Kessler notes, then stops. He sobs once, his knees buckle, and he drops face-down on the floor of his House.

David Kessler holds a naked mole rat at the Small Mammals House at the National Zoo. (Logan Mock-Bunting/For The Washington Post)

Earlier in the day, Kessler talked about his career. “I like to work with animals that nobody thinks about,” he said. Small mammals, it’s true, are not headliners. Hey, kids, let’s go see the shrews! In the past few years, Kessler has been lavishing his attention on the naked mole rat, an animal that resembles a flaccid penis with buck teeth. He always has a favorite weirdo. He has been the red panda guy, the house shrew guy, the Prevost’s squirrel guy and the moonrat guy. Moonrats have no natural predators, Kessler says with admiration and a little pride, because they smell so bad.

There aren’t a lot of jobs like zookeeper. Technically, Kessler’s job has been biologist, but the caretaking — the keeping — is what he loves best.

“It’s the care of living things. To keep, that’s a beautiful thing. The longer you watch an animal or a person just doing their thing, the more you feel connected to them.”

A keeper feeds the animals and mucks out their enclosures, but the real work is observation, watching their bodies and behavior closely for subtle changes that mean something is wrong. And figuring out how to fix it.

Take the lemurs, smallish primates with doglike faces, some of the most social creatures in the Small Mammal House. Cortes and Coronado are recent acquisitions — Kessler drove them down from the Bronx Zoo in his Honda Civic— who are being carefully phased in with Molly, who has been the sole lemur at the Small Mammal House since her mate died. The keepers noticed the new lemurs were keeping low to the ground, un-lemurlike behavior. Lemurs are at home in treetops, and the damp ground was irritating one of Cortes’s paws. Perhaps Molly was being territorial. They would wait and see, maybe give Molly more attention. And keep watching.

Kessler and his colleagues would eventually determine Molly wasn’t behaving aggressively toward the other two lemurs. A volunteer noticed it was the rock hyraxes antagonizing Cortes and Coronado. The rock hyraxes were moved to a different exhibit and, voilà, the lemurs returned to the trees.

Lemurs are comparatively easy to read. You can spend less than half an hour watching Molly and feel as if you almost understand her thought process. You can become so absorbed you forget who and what you are, and that you are watching. It can become like reading a novel, the closest humans can get to having someone else’s consciousness for a change.

It took a year and a half in the reptile house, but eventually Kessler could tell when something was wrong with a snake.

He’s about average height, and he has had a beard most of his 59 years, but not now. He wears khakis and polos to work, with big rubber boots, disposable gloves and face masks. Primates can pass each other disease easily, he says. A keeper’s herpes cold sore can kill a gorilla.

In conversation, Kessler tosses out bits of philosophy, science, novels, plays — knowledge you should have, if you had time to read, and he acts as if you probably know them, too.

He knows each of the hundred-odd residents of the Small Mammal House by their six-digit reference number. He has also published or co-written about a dozen research papers. Written three unpublished novels. He once went on a radio show to compose sonnets on demand. He mentors high school students and oversees their research projects. Every year Kessler takes off work to see as many shows in the Capital Fringe Festival as possible, since they often run past midnight and his work would start at 6:30 a.m. He spends an hour a day on the treadmill. He lives in Silver Spring and has been married for 30 years — he still writes his wife, Patricia, sonnets. He smiles when he happens upon a picture of her unexpectedly. They have a grown son, Ben, who co-owns an urban farming company in Charlottesville.

When friends asked, he officiated their 2006 wedding, working with them to write a personalized service, complete with sermon. Kessler took lessons from an actor friend on how not to cry. He always cried at weddings but didn’t want to distract while performing one. He was asked to officiate another wedding in Rockville, even though he was racing to New Jersey and back to be with his dying father. His father died. Kessler made the arrangements so his mother and sisters wouldn’t have to, then drove from New Jersey to the rehearsal dinner that night. When another friend needed him to, he was the one to officially identify her husband’s body.

For a while he fronted a calypso-reggae band. He is universally beloved among colleagues and friends — suspiciously so, if you are a person suspicious of that sort of thing.

Kessler gives a "Meet-a-Mammal" presentation with naked mole rats. (Logan Mock-Bunting/For The Washington Post)

Kessler’s last “Meet a Mammal” demonstration for zoogoers, on his last day at work, was attended by Linda Hopkins, a zoo electrician who’d known him 11 years and brought him a bottle of wine, and Susie Kane, who had never met him, but she had heard he was leaving, and in 2005 he had kindly answered her e-mailed question about building a naked mole rat habitat for her dorm room.

In December, Scientific American declared the naked mole rat Vertebrate of the Year. He is a happy man who’s leaving the job he loves.

He’s retiring young because of his psoriatic arthritis. It’s much better these days — he gets injections of monoclonal antibodies. But it is progressive. “I only have so much health left,” he says, and zookeeping is physically taxing. He wants to travel with his wife, and write.

A loved one once told him that he would probably be happier as a hermit. He wasn’t insulted.

“I’m more comfortable by myself and with animals than I am with people,” he says. “I don’t feel like I fit around people.” Around people, he is giving a sort of performance. “But an honest performance.” Sometimes he loves it, performing, fronting a band, officiating at weddings. “There’s tension, but fun tension, like scary movies. I like the attention and the tension.”

So ask to watch him work, ask him to ignore you, and it doesn’t work. That’s a private part of him, reserved for himself and the animals. He’ll start offering you books or telling you stories, and if you patiently sit around, pretending to use a computer in his office until he forgets you’re there, he will not forget you’re there. He will grow slightly agitated and need some alone time with the lemurs after you’re gone.

David Kessler chokes up as volunteers say goodbye to him. (Logan Mock-Bunting/For The Washington Post)

His last day is a whirl of well-wishers, friends, leftover food from the party the day before, paperwork, gifts, tears and hugs. “I don’t like to be touched,” he says to one hugger, “but being hugged is fine.”

He hadn’t been assigned to do the lines that morning — the shift that starts before sunrise, when the animals get their breakfast and their enclosures are cleaned out. He had e-mails to read, but people kept coming by for hugs and predicting he’ll be back. He says no, never coming back. He seems to mean it.

Even friends who aren’t physically present are distracting him. “Happy birthday to you,” he sings into a friend’s voice mail, gargling the last line. “Happy Jimmy Page’s birthday, happy your birthday, happy your aunt’s birthday yesterday.” He attends to the needs of the humans for hours, their need to say goodbye, to say they would miss him. He almost always has a specific memory or thought for each, as he thanks them and assures them he won’t miss this place and, after some time, they won’t miss him.

He’s proudest of his work with William the gibbon in 1978. William was a juvenile living with his parents when he got stuck in the enclosure and broke his arm. He was in the hospital so long — so long in the company of humans — that his parents rejected him when he got back. And because his hospital experience was scary and painful, people now made William fearful and angry. He was kept out of the exhibit for a while, off by himself.

Kessler sat in his enclosure each day, doing nothing except being nonthreatening. No mask, no gloves. Back then, this was acceptable zookeeper behavior — interaction not initiated or welcomed by the animal.

William would brachiate around in the farthest corner from Kessler, swinging limb to limb, elaborately ignoring the 130-pound human in the room. Over the course of a week, William came closer and closer, until his feet would brush his keeper’s head as he swung by. Eventually he would put his head on Kessler’s sweatshirt and go to sleep. There’s a picture with William’s arms around Kessler’s head.

One thing he will miss from the zoo: watching the howler monkeys eat. Jolla likes beets but not the squiggly end of the taproot. She will pick it up, put it down, eat something else, return as if to see if the bit she doesn’t like is still there. Maybe it got better! You can learn so much about optimism from her, Kessler says. “People tell me she’s just stupid,” he says, shaking his head at that human stupidity.

David Kessler kisses an Aldabra giant tortoise in this undated photo. (Courtesy of the National Zoo)

Twelve years ago, Kessler walked with a cane, couldn’t turn his head and could sleep only an hour and a half at a time because of his arthritis.

Thirty-six years ago he called his psychiatrist to say he had everything ready to commit a tidy, no-fuss suicide, just a hose and towels in a car exhaust pipe. His doctor had him hospitalized for four days.

Then, at 27, he taught himself to be happy. “You learn from evolution, from animals. If you have a strategy that doesn’t work, change your strategy.”

His new strategy was to avoid introspection. Completely. “Working with animals made me start thinking about other things more. And when I was able to start thinking about other animals more, I was able to include humans in that group.” Understanding William the gibbon, for example, and building his trust, was a big “breakthrough with myself.”

“The real change was Patricia,” he says. “But I probably couldn’t be with her if I hadn’t been working with animals.”

According to dominant psychology and philosophy, introspection is the key to living right. But Kessler’s unexamined life is the only kind he wants to live.

For obvious reasons, it’s difficult for him to explain how he stopped being introspective. Working with animals is one way, but there were others. When he worked alone off-exhibit, he narrated his novels in his head. He noticed that closing certain doors in the building was musical, producing two notes, a seventh interval: the first two notes of a song from “West Side Story”: “Somewhere.”

Kessler takes out the trash for the last time. (Logan Mock-Bunting/For The Washington Post)

Sometimes he needs to go alone to see if Molly wants a belly rub. Lemurs and Reuben the howler are the only ones in the Small Mammal House to much enjoy the touch of a human. But lemurs are not pets. They did not evolve to be companions for humans, to cheer us up or give us something to love. Molly indicates if she wants a belly rub, not unlike a dog, and a keeper may administer it, but the belly rub is entirely for the animal. That’s important to Kessler.

It turns out Molly wants a belly rub on Kessler’s last day, after he has finally gotten rid of all the people and sneaks off to see her.

Afterward, he keeps putting off leaving, until his shift stretches to 11 hours. And because the rock hyraxes have been moved away from the lemurs they were scaring, here’s Gus, too present-focused to understand “goodbye” but seeming to say goodbye, popping his head up, watching the keeper leave for the last time, and the keeper — finished with crying, hugs and goodbyes with people — goes down, face first.

Suzanne Hough, the volunteer coordinator, is leaving with him, and she joins him on the floor. “I’m sorry, I’m sorry,” he says. “No. No, no, it’s okay.”

After a moment, Hough speaks. “The floor can be tricky this time of night,” she says, generously. She helps him up. He’s fine, as far as he lets anyone know.

Moments later he is calm again, and performing. “Well, that was a surprise!” he says breezily. Hough and Kessler walk out into the cold night.

Inside the House, the hundred-odd residents have no sense that their time as keepers of David S. Kessler has come to an end.

Rachel Manteuffel is an editorial aide in the Editorial Department. To comment on this story, e-mail or visit