Back From The Brink Of Extinction, This Little Warrior Is the Size of Your Thumb

Researchers at the San Diego Zoo may have just successfully bred the diminutive ‘pocket mouse.’
The size of a human thumb, the pocket mouse was one believed to be extinct. (Photo: San Diego Zoo Global)
Jun 8, 2013· 2 MIN READ
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The first critically endangered pocket mouse bred in captivity should be giving birth within the next week at the San Diego Zoo’s Pocket Mouse Breeding Facility.

In an in-field interview this morning, pocket mouse researcher Debra Shier, Ph.D., told TakePart that the mouse, named Female #13, mated with another captured pocket mouse, Male #25, back on May 29. On her blog from that day, Shier wrote:

“I was crossing my fingers anticipating the first interaction. Female #13 came out of her tube first and started sand bathing. Male #25 emerged about a minute later. They approached each other a couple of times and then immediately began following each other in a tight circle. They were moving so fast that they looked like a spinning pinwheel with their little tails flying behind them. After only 30 seconds, they were mating. SUCCESS! The whole event was over in about eight minutes, and the next time the male approached the female, she tried to bite him on the head and ran away.”

If the mating is successful—and it appears that it was—it will be a boon for both the zoo and the U.S. Department of Fish and Wildlife.

According to Shier, from a genetic perspective, the pocket mouse more closely resembles gophers or squirrels than the invasive house mice. A typical pocket mouse weighs just seven grams and is the size of half of a man’s thumb.

No one knows exactly how many live in the wild, but the few they know of inhabit a three- to five-mile swath inland of the Pacific Ocean between Los Angeles International Airport and the Mexico border. Shier says that humans “like the same habitat as the mice do,” which is why their homeland has been so overdeveloped.

In the 1980s, they were considered extinct. But in 1993, they were discovered—in Dana Point, California, and in two areas on the Camp Pendleton Marine Base.

They’re crucial to the environment, says Shier, for several reasons, including that they’re “primary seed dispersers” for disappearing coastal sage scrub, and that their burrows provide habitat for many different species.

But to Shier, who also studies kangaroo rats, the most amazing thing about them is how their “enlarged inner ears” may mean that they communicate through “foot drumming.” So far, no one has been able to study them enough to know this for certain. But in addition to trapping them for breeding, Shier is also conducting a study about foot drumming.

“We really know very little about them,” Shier adds, “because at their size, they’re so difficult to watch in the wild. I was out the other night with my nightvision goggles, and I could barely see them.”

But two and a half weeks ago, Shier and her assistants captured several mice from the three different areas. They brought them to the breeding facility and began trying to matchmake. Female #13 and Male #25 hit if off.

Since then, Female #13 has “gained weight and her nipples have bared (shed their fur, for lactation).” says Shier. For the past few weeks, she and another impregnated female have had food supplemented with powdered milk and have been given larger-than-normal cages.

“They’ve been treated like queens,” says Shier—which, with luck, will help Female #13 give birth next week.

Shier and her colleagues are anxiously awaiting the outcome. But after three weeks, a wild pocket mouse weighs just three grams. “No one knows how tiny the babies are when they’re just born,” says Shier, because they’ve never been seen. But she—and everyone else—will soon know.

What other tiny creatures do you hope are the next focus of conservation efforts? Let us know in the Comments.