Around this time of year, birders flock to forests and lagoons en masse, hoping to top last year’s tally for the annual Audubon Christmas Bird Counts.

While that century-long tradition helped establish San Diego as a hotspot for biological diversity, the mammals that share those woodlands and waterways have remained largely incognito.

A new volume from the San Diego Natural History Museum, the “San Diego County Mammal Atlas,” will help fill that gap, offering views of the county’s warm-blooded inhabitants, from bats to bighorn.

“This book is really designed to illuminate all the wonderful mammals we have,” said Scott Tremor, a mammalogist with the museum and editor of the atlas. “This county is more bio-diverse in mammals than any other county in the country. We’re finally bringing all this information together that has taken 17 years to compile. Hopefully, it will help people get answers to all the questions they have, and really open their eyes to what we have in our region.”


The book, set for release Dec. 19, follows the museum’s authoritative bird, reptile and plant atlases, and seeks to round out the record on San Diego’s abundant animal life. The 432-page volume includes all 91 terrestrial species and 31 marine mammals recorded in San Diego since 1769, along with rich images.

“All these wonderful photos help people identify, ‘Oh, maybe that’s what I saw,’” Tremor said.

Take, for instance, the long-tailed weasel: the sleek, russet creature poised on the atlas cover.

You may have seen a streak of auburn scurrying through a park or yard. Or you might not know that weasels live in San Diego. They’re here, inconspicuous but thriving.


“The long-tailed weasels I think are plentiful,” Tremor said. “The population is in great shape, and widespread…. They’re just elusive — you just don’t see them very often.”

Weasels are nomadic and voracious predators that devour entire colonies of gophers and ground squirrels before moving on to the next rodent buffet. And they have distinctive features.

A long-tailed weasel, one of the mammals depicted in the new “San Diego County Mammal Atlas. (John Mitchell )

“The black-tipped tail, the mask, the orange, rusty pelt and the movement — the slinky, sinuous behavior is really the giveaway,” he said.


Another lesser-known resident is the ring-tailed cat or miner’s cat. Not really a feline, it’s a relative of the raccoon.

“They’re just beautiful animals,” Tremor said. “The miners used to train them to eat rats in the mines.”

The atlas also highlights curious behaviors of some local mammals: the Mexican long-tongued bat that sips nectar of night-blooming plants; or the badger, which hunts in tandem with coyotes.

“The badger will start digging out a hole (into a squirrel burrow) and the coyote sits on the other end waiting for that ground squirrel to come out,” Tremor said. “Sometimes the ground squirrel comes out and sees the coyote, and runs back to the badger.”


Either way, one of the predators gets a meal, he said.

The tome also introduces the smaller mammals of San Diego. One of the rarest is the endangered Stephens’ kangaroo rat, said Wayne Spencer, a co-editor of the atlas and chief scientist at the Oregon-based Conservation Biology Institute. Their highly specialized diet has left them vulnerable to habitat loss, landing them on the endangered species list nearly 30 years ago.

More closely related to squirrels than actual rats, kangaroo rats have acute hearing and vision, with long tails and powerful hind legs that let them bound like tiny kangaroos.

“They’re beautiful little creatures, very gentle, very clean, seed-eaters,” he said.


At the other end of the spectrum is the minuscule, but mighty grasshopper mouse, a carnivorous rodent with daggers for teeth and an appetite for dangerous prey.

“They’re like tiny little rodent wolves,” Spencer said. “They even howl like wolves when they come out of their burrows in the evening. They have stiletto-like teeth for -- it may be gruesome -- killing other mice, insects and scorpions. They eat all these other things that other species can’t eat.”

Tremor had his own harrowing encounter with a grasshopper mouse, and another local mammal, on the eve of the Cedar Fire in 2003. He caught one of the little rodent thugs and popped it in a terrarium for photos.

“As I was photographing it, I was so excited,” he said. “When I looked up, I saw eye-shine 30 feet from me. It was a lion that was circling me. I just picked up the terrarium and walked backwards to my car. The animal slowly followed me, but nothing happened. My adrenaline was pumping. I let the mouse go.”


That’s the kind of encounter that makes mammals harder to study than other species, the researchers said. Many of the animals are nocturnal, they’re evasive, and not at all happy when they’re caught.

A canyon bat in flight is pictured in the “San Diego County Mammal Atlas.” (Anthony Mercieca and Charlie VanTassel )

“We dedicate ourselves to often terrible hours in harsh conditions, very very hot, very very cold, capturing animals and releasing them,” Tremor said.

Even the larger mammals -- so-called “charismatic megafauna” such as mountain lions and bighorn sheep -- are also solitary or seclusive, and equally hard to spot and study.


The researchers hope the atlas will shed light on some of those animals, and help people see -- and potentially save -- some of the creatures they highlight.

Although mammals have gotten short-changed in the region’s habitat conservation plans, the atlas could help right that by illuminating the conditions and habitat they need, Spencer said.

“It’s a really good foundation moving forward for landscape planning that includes the mammals, which frankly have been somewhat neglected in our conservation work,” he said.

With detailed descriptions and distribution maps, it could inspire readers to explore new parts of the county to see elusive creatures, Tremor said.


“If someone went out to Borrego Canyon in the middle of the night, just to find a ringtail, they’re moving about there,” he said “We have this reserve land, publicly held open space, that will never be built upon, and harbors a wonderful diversity of wildlife.”

The book will sell for $49.95 in the museum store and online at https://www.sdnhm.org/. Proceeds will support the museum’s Department of Birds and Mammals. The museum will host a Nat Talk and book signing on Tuesday, Dec. 19 at 7 p.m., the release date for the atlas.


deborah.brennan@sduniontribune.com Twitter@deborahsbrennan