Conservationist Jeff Corwin is known for often bringing a goofy passion to his television projects for Animal Planet and other networks. His latest effort displays no less passion, but switches out most of the jokes for gravitas.

100 Heartbeats: The Race to save Earth's Most Endangered Species, Corwin's new book and accompanying MSNBC documentary, is a compelling portrait of several endangered species we are about to lose—many of which have fewer than 100 living individuals, hence the "100 Heartbeats" of the title. It is equal-part adventure story, travelogue, history lesson, environmental textbook and investigative journalism as well as a portrait of some of the people trying to save endangered species. Perhaps most importantly, it also serves as a call to action.

The project got its start two years ago, while Corwin was editing a previous documentary called "The Vanishing Frog". Corwin says his young daughter saw an image of the Panamanian golden frog (Atelopus zeteki) on screen and asked him if he could take her to see it. Corwin explained: "I said, 'I can't. That was the last wild frog ever seen. They no longer exist in the wild.' She looked at me and said, 'Dad, you failed.'"

"That was a very difficult conversation to have, about extinction. And that was the day I started writing the 100 Heartbeats book," Corwin says.

The book, which he calls an "intense labor of love," is obviously very important to him. "This, for me, was the book I've always wanted to do, and the documentary I've been waiting to do," Corwin says. "During this conversation with my daughter, I realized that many of the species I had filmed over the years have become critically endangered or even extinct. I wanted to ask, what does it mean when we push a species to the brink? Is there any way we can save them? What can we do to move forward?"

Corwin spent two years researching and writing 100 Heartbeats, traveling all over the world to examine issues such as the amphibian-killing Chytrid fungus, elephant and rhino poaching, shark finning, the bushmeat trade, and the destruction of Indonesia's rainforests. Along the way he met many of the experts and hard-working people helping to save species such as the California condor, the golden bamboo lemur, the Indian one-horned rhino, and the red wolf, a critically endangered species just barely numbering 100 members.

"I wanted it to be inspiring and happy and sad, and use the real-life drama of the species in peril and the people trying to save the species," Corwin says.

Of all the species he examined, Corwin says, the black-footed ferret most embodies the "100-Heartbeat club," both in terms of how close the ferret came to extinction and how far it has come since then. "This is a creature that in the 1970s was declared extinct," he says. "Now there are 2,000 of these animals. I followed them very early in my television career. I thought this species would never truly be wild again. Cut to 14 to 15 years later, with my daughter at my side, and I'm opening up a little carry case and this tiny, furry, slinky creature comes hopping out, mad as hot tar, squeaks at us, and disappears into its new home. It was one of 14 animals to be released into the wild that day, and I got to share that with my daughter." This was the same daughter, by the way, who kicked off the 100 Heartbeats project by asking about the Panamanian golden frog.

Despite conservation successes like this, Corwin acknowledges that the bigger picture often looks bleak. "I'm really scared," he says. "Chytrid, white-nose syndrome, colony collapse disorder, these all tell us that something is amiss. Climate change alone could kill 20 percent, maybe more, of our planet's species. It's the first time that one—man—is the catalyst behind all of this.

"We lose resources, things we depend on, when we lose these species," he says. "They're our partners in agricultural management, in managing ecosystems. We lose food, energy, potential medicines. Not only do the species lose out, we lose out. The quality of life and living of the next generation would be put in jeopardy."

Image: 100 Heartbeats cover, courtesy of Rodale Books