A Little Bit Batty

It’s mid-June. The sun has just dropped down behind the rolling hills to the west of my building. The sky, in its wake, is deepening into shades of lemon and cantaloupe. A cool breeze has come up, and the fog is sending its first tentacles over the hilltops. 

I dig a pair of shoes out from under the dining room table and strap them on. Tanner watches me with an intensity he normally reserves for squirrels. When I stand, he leaps up and dashes into the bedroom, doubling back to the doorway to make sure I’m still behind him. He circles around me and sits when I pick up his leash. He’s doing his best to be calm, but when I turn to grab my keys off the shelf he can’t resist a quick, excited nibble at his already well-frayed leash.

Tanner stands watch over the walkway as I lock the door. Then there’s the elevator and a stroll through the courtyard to get the business end of the walk out of the way. Finally I push the front gate open and we cross the street to the park.

The sky is darkening to a deep, iridescent indigo. Streetlights flick on. We come to a long, open patch of grass that separates the ball diamond from the bocce courts. Tanner’s head is down. With his hunting-dog nose, he’s minutely studying and cataloging the scents that have accumulated in the grass, tree trunks, and plants since our walk first thing this morning. 

I, however, am looking up. It’s almost time for the bats to come out.

We reach the light pole at the south end of the park. I see a jagged fluttering at the edge of my vision, then another. A bat cruises by, a few yards over my head. As quickly as the bat appears, it reverses direction and is gone. Within seconds it - or one of its companions - is back. I move away from the light and keep watching.

It’s difficult to tell exactly how many there are, since they are well camouflaged by the darkness and their movements are quick and jerky. After a few minutes I determine that there are at least six individual bats over the immediate area. They do an intricately choreographed dance across the park, threading in and out of each other’s paths, ascending steeply, executing sudden u-turns and death-defying dips and dives. 

I’ve been fascinated by these hairy, insect-eating neighbors of mine for weeks. Yesterday evening, as usual, I timed the end of our walk to coincide with prime bat-watching time. The lights at the ball diamond were on and insects were swarming around them. I figured it would be a good night for bats. Yet in the ten or fifteen minutes we spent milling about, I only saw one bat.

During June and early July I had observed that the average window of time the bats spent in this section of the park nightly was about forty minutes, after making their first appearance around dusk. In the past couple weeks I’ve noticed their numbers decreasing, but last night's solitary bat was an all-time low. 

Bats are nocturnal. Like birds, they must eat at least half of their body weight in food daily to maintain the energy they need to survive. I wondered: Is there a route they follow each night, with regularly scheduled appearances to mine each spot for insects before moving on? What kind range do they cover when hunting - blocks, acres, miles? What would cause them to pass over a place they frequented previously? And finally, where do they sleep during the day? 

It was time to find out. I gave Tanner his post-walk treats and immersed myself in the world of bats. 

I discovered a wealth of information that answered my biggest questions. If you'd like to explore for yourself, see the links below for bat-resources and further bat-info:

 - Bats date back at least 35 million years, possibly longer+. Of the 47 species of bats common to the United States, about 24 are local to California•. Thirteen species are native to Marin County*, where I currently reside. One of the most common is the Myotis lucifugus, or little brown bat. 

Myotis lucifugus photo courtesy of http://www.emnrd.state.nm.us/MMD/AML/Bat-LittleBrown.html 

- Bats are beneficial to the ecosystem, controlling insect populations (one little brown bat can eat up to 1000 mosquitos in a single hour** ) and significantly reducing the types of insect pests that plague crops. Many species play vital roles in pollinating plants, flowers and trees. They catch insects with their mouths, or use their tails to trap insects and direct them mouthward. 

- Despite the saying 'blind as a bat', they are sighted animals. Small bats like the little brown bat use echolocation to hunt prey, while their vision helps them navigate large obstacles++.

- Bats are known to travel several miles per day between roosting and feeding sites, they are likeliest to stay relatively close to their roosts. They're most active a few hours after dusk and a couple hours before dawn, sometimes heading back to the roost for a nap in between. They tend to return to areas where they have found food before. Bats are partial to beetles, which are large, easy prey ∆ (this may account for the large numbers of bats I saw earlier this summer when the June bug -June beetle- population was booming).

June bug photo courtesy of http://digitaldreammachine.blogspot.com/2006_06_01_archive.html

- It's commonly known that bats reside in caves, and under that one bridge in Austin, Texas (http://www.roadsideamerica.com/story/10852 - a 'World's Largest'!). Smaller species can fit into any opening greater than about half an inch, so any dark, warm sheltered place, including under rocks and inside wood piles, can be a roost. 

- While it’s easy to think of them as birds, bats are mammals. A female little brown bat gives birth to one pup per year, and it clings to her for a few weeks while nursing. After about a month, the pup can fly on its own and is self-supporting ∆. 

   

It’s about time for this evening’s walk. My soundtrack tonight, in honor of the bats, will be the Batman Begins score. Hans Zimmer and James Newton Howard named each track after a different species of bat!

Links:

+Natural History Museum of the UK, http://www.nhm.ac.uk/nature-online/life/mammals/bats/session1/index.html, and ++http://www.nhm.ac.uk/nature-online/life/mammals/bats/session3/index.html

•San Francisco Bay Area National Parks, http://www.sfnps.org/bats

*WildCare eNews Letter, October 2008: http://wc.convio.net/eNews/October_2008.html

**Defenders of Wildlife, Bats Fact Sheet: http://www.defenders.org/bats/basic-facts

∆ University of Michigan Animal Diversity website: http://animaldiversity.ummz.umich.edu/site/accounts/information/Myotis_lucifugus.html