On a day when other candidates were preparing for a major debate, Newt Gingrich spent the morning with Barnaby, an 85-year-old tortoise at a Des Moines zoo.

It might have been viewed as one more possible sign that the former House speaker isn’t serious about his presidential aspirations. Turns out it was merely Gingrich indulging in one of his favorite pastimes as he plodded his slow, steady course to the front of the Republican pack.

Gingrich, it seems, is crazy for zoos.

Earlier this year, Gingrich took to Twitter to express his sadness at the untimely death of Knut, a polar bear with an eerily familiar name he had visited at the Berlin Zoo. On the campaign trail, he has occasionally relaxed by stealing away to a reptile house or giraffe enclosure to commune with wildlife.

Gingrich’s first act of civic engagement was at age 11, when he lobbied officials in Harrisburg, Pa., to open a zoo. “Young Newton Gingrich told Mayor Claude Robins and four city councilmen that he and a number of youthful buddies could round up enough animals to get the project started,” the Associated Press reported in 1954.

Gingrich’s passion for this childlike hobby is not just a quirk. Fascinated with nature and wildlife since he was a boy, Gingrich speaks often of his deep appreciation for the natural world and the importance of protecting the environment for future generations. In Congress, he backed the Endangered Species Act against the wishes of many in his party, and he has spoken out in favor of measures meant to curb global warming.

He has softened his stance on climate change lately, saying there are merits on both sides of the debate. Still, he acknowledges that he is an environmentalist, albeit from a free-market perspective.

In a 2007 book he co-wrote, “A Contract with the Earth,” he argues that humans have a God-

given responsibility to be stewards of the environment and that the private sector can help the country become the world’s leader in environmental policy.

His interest in zoos goes beyond policy; it is a relic of his childhood and an escape from the demands of his daily life.

“I just like to go and unwind, and see how the local zoo does things, the kind of animals they have,” he said in a recent video on YouTube.

As a congressman in the 1980s, Gingrich approached Zoo Atlanta for a backstage tour. Zoo Director Terry L. Maple escorted him from exhibit to exhibit, fielding questions for about an hour before having to excuse himself, leaving Gingrich to spend two or three more hours lobbing queries to the curators.

“I have never taken anybody, a VIP, through a zoo who wanted more than a brief tour and a photo op,” recalled Maple, Gingrich’s co-author on the environmental book. “You knew it was something kind of different for him, something special.”

Gingrich, who wrote the foreword to the guidebook “America’s Best Zoos,” says he has been to nearly 100 zoos in the United States. He visited at least three while on the campaign trail this year and hosted a campaign fundraiser in September at the Lowry Park Zoo in Tampa. For the time being, the cold weather and a demanding campaign schedule have forced the candidate to curtail his zoo visits, a Gingrich spokesman said.

In a 1995 Vanity Fair profile, Gingrich told how he had been a solitary child, filling his time by collecting lizards, fossils and snakes. (His second wife, Marianne, apparently picked up on this early interest, buying him an emerald tree boa that the couple housed in the bathtub.)

As a child, he devoured books about famous zoo directors, including the Bronx Zoo’s Raymond Ditmars and National Zoo visionary William Temple Hornaday, whose credits also include saving the American bison from extinction.

Gingrich once dreamed of being a zookeeper or a vertebrate paleontologist, he has said in interviews, perhaps presaging the T. rex skull that would one day grace his speaker’s office.

While in Congress, Gingrich helped Zoo Atlanta acquire a black rhino he named Boma, after former Georgia congressman Howard “Bo” Callaway, a political mentor.

And after resigning from Congress, as he pondered his next steps, Gingrich stipulated to his advisers that he must not be robbed of time to indulge in his favorite hobbies — reading, learning and visiting zoos.

Zoos are such a part of Gingrich’s thinking, he recently reached for a zoo metaphor in criticizing the Obama administration.

“It would be like taking your child to the zoo and explaining that a lion is a bunny rabbit, and [it] was really okay to get in the cage and play with the bunny rabbit, and then you were shocked that the lion ate the . . . your . . . I mean, that’s how far out of touch with reality the Obama administration is,” he said in an interview with the Jewish Channel.

The idea to open a zoo in his childhood home of Harrisburg struck the young Gingrich after an afternoon matinee of two animal films, he wrote in “America’s Best Zoos.” As he left the theater, he saw a sign for City Hall, walked through the front door and asked how to go about the task. A park official, who happened to be an old flame of his grandmother’s, explained that there had been a zoo previously but it was closed because of rationing during World War II.

The old man suggested that he take his case to the city council. Gingrich’s effort ultimately failed to get the city a zoo but managed to launch a successful career in politics.

Staff researcher Lucy Shackelford contributed to this report.