NEW YORK, NY.- Petra Mathers, a German-born children’s book illustrator and author whose kindly, often bumbling animal characters were nonetheless quietly heroic and often risked much for love, died Feb. 6 at her home in Astoria, Oregon. She was 78.

Patty Flynn, her executor, said Mathers and her husband, Michael, a photographer, who was 79, took their own lives. There did not appear to be an obvious health concern that precipitated their act, although they had often told friends that they could not live without each other. They were a private, devoted couple, and the timing of their deaths remains a mystery.

With spare, naive images rendered in ink, pencil and watercolor, Mathers’ stories — whose subjects included a soulful museum guard (an alligator) who falls in love with the subject in a painting (another alligator) and a warmhearted chicken named Lottie and her best friend, Herbie, a duck — were just as sparely written, but imbued with sly humor and wit, captivating both her 8-and-younger audience and their parents.

“Here is the story of a chicken who flees the coop,” Carol Brightman wrote in 1985 in a New York Times review of Mathers’ first book, “Maria Theresa,” a tale of a dreamy fowl who has all sorts of adventures. “You know the type. No ordinary laying hen, this one sometimes stops ‘in mid-peck as if listening to faraway voices.’”

Mathers’ prose and her “flat, old-fashioned cutout surrealism” combined “an attention to both the commonplace and the arcane which marks the best of children’s literature,” Brightman wrote. “The book’s final tableau of circus folk (and fowl) dancing the Tango Argentine outside Miss Lola’s Airstream is a triumph of this vision. What else but a hopelessly romantic chicken, one that never forgets to lay the morning egg, could bring us such a show.”

Other reviewers compared the loopily unfurling tale to a Federico Fellini film.

Mathers had already written four books when she began her Lottie series in the late 1990s. An interviewer asked her: Why focus on chickens? “I can make them move, draw them to express feelings,” she replied, adding: “Lottie is my role model. Even though it seems that I am inventing her, she already exists in all of us when we are at our best.”

“When Aunt Mattie Got Her Wings” (2014), Mathers’ last book, foreshadowed one of her last acts, a decade later.

Mattie is Lottie’s beloved aunt; here she is 99 years old, and dying, and Lottie travels to the hospital to say goodbye. Aunt Mattie wakes up to greet her. “They’re expecting me upstairs, but I told them I was waiting for you,” she says. “Oh Lottie, what fun we’ve had.”

And off Aunt Mattie goes. It’s not clear where, but there’s an airplane waiting for her — a flight on “Out of This World Airlines” — and lots of other chickens. Everyone looks pretty happy. Back home, Lottie finds a note waiting for her.

“By the time you read this I will be dead,” it says, “and I imagine you’re feeling a little down in the beak. That’s why I’m writing this letter. I’ve had a long and happy life doing what I love best.” Aunt Mattie adds, “Now it’s time to make room for someone else on this earth.”

Petra Tollens was born March 25, 1945, in Todtmoos, Germany, a small town in the Black Forest, and grew up first in Stuttgart and then in Wiesbaden, where her father, Ernst Tollens, was a representative for a Champagne firm; her mother, Carola (Glass) Tollens, worked part time in an office.

“I was always drawing for as long as I can remember, but not well,” she told Dilys Evans, author of “Show and Tell: Exploring the Fine Art of Children’s Illustration” (2008). After high school, she worked in a bookstore and for a publisher of encyclopedias before moving to Oregon in the mid-1960s with her husband at the time, Eberhard Richter. She worked as a server and painted, exhibiting her work in local galleries. She later met Mathers in what was by all accounts a coup de foudre; they were married in 1980.

For a few years, the couple lived on New York’s Long Island, and when Laura Geringer, an editor at HarperCollins, saw Mathers’ artwork, she commissioned her to illustrate “How Yossi Beat the Evil Urge,” by Miriam Chaikin, which was published in 1983. Mathers and Geringer would go on to collaborate on a number of books; Mathers illustrated the work of other authors, too. Over the decades, Mathers illustrated more than 30 children’s books — a process she described as “visiting,” requiring “a certain politeness, consideration and modesty” — and wrote 10 titles of her own. In 1988, her second book, “Theodore and Mr. Balbini,” about a precocious dog who learns to speak and leaves his owner for a French teacher, was named one of The New York Times’ best illustrated children’s books of the year.

For the past 17 years or so, Mathers and her husband lived in a spare modern house on a hill in Astoria overlooking the Columbia River. Michael Mathers’ own work documented the life of the town and its local characters. Petra Mathers was a procrastinator and always feared, as she told an interviewer, that “any moment the children’s book patrol will drive up and take all my stuff away and seal my studio.”

“But all the while, slowly,” she added, “a story comes together, crude and on wobbly legs.”

Like Aunt Mattie, Mathers and her husband wrote letters announcing their death, thanking loved ones and colleagues for their friendship — and noting that they were happily going elsewhere. They were not religious. (“Trying to be good” is how Mathers answered a line in a questionnaire regarding religion.) The recipients were stunned at first, but many were not exactly surprised.

“They believed their marriage was the most complete relationship ever,” Barbara Hansel, a friend and a former bookstore owner, said by phone. “They often said they could not live without the other. They did what we always knew they would do. It confirmed the truth of their marriage.”

Over the years, Mathers had donated much of her original artwork, including all the work for the Lottie books, to the Eric Carle Museum of Picture Book Art in Amherst, Massachusetts. It was a natural fit, said Nichols Clark, the museum’s founding director and chief curator emeritus. “They both used humble animals to tell very big stories,” he said of Carle, author of “The Very Hungry Caterpillar,” and Mathers.

Clark received one of Mathers’ goodbye letters. She wrote that she and her husband had “become frail, physically very little, mentally not so little.” She noted that by the time Clark would receive his letter, the couple would be in their shared grave in Oysterville, Washington. “You can hear the ocean and the cows often come to graze early evening,” she wrote.

She wrote of the pleasure she took in being part of the Carle museum, and she included an unpublished manuscript and a generous check.

Mathers is survived by her son, Tillman Richter; a grandson; and her brother, Gero Gerweck. Her marriages to Richter and David Spence ended in divorce.

“Petra was really very important and not as celebrated as she deserved to be,” Anne Schwartz, Mathers’ longtime editor, said by phone. “Each book is a slice of life beautifully captured, a little gem. She was a keen observer of the minutiae of the world around her, the small dilemmas of life. And she was a romantic to her very bones.”

“Sophie and Lou” (1991), one of Mathers’ early titles, was the story of a mouse who overcomes her painful shyness and learns to dance, with the help of an equally bashful suitor. The dedication, which Mathers wrote in ink and adorned with winged hearts, reads, “To Love, and those who dare put all their eggs in one basket.”

This article originally appeared in The New York Times.