The Real Bats of San Diego County

The three most commonly detected bat species in western San Diego County are: Yuma myotis (Myotis yumanensis), Mexican free-tailed bat (Tadarida brasiliensis) and big brown bat (Eptesicus fuscus). All three are insectivores which is a real benefit to the humans in the community. A bat can eat thousands of insects each night; including moths, beetles, flies and mosquitoes! 

Yuma myotis are quite tiny— with a body length of only 1.5 to 1.9 inches, and weighing less than half an ounce! They are named for the first placed they were described in 1864—Yuma, Arizona and myotis means mouse-eared. They specialize in eating emerging aquatic insects such as mosquitoes! Read more

Mexican free-tailed bats are named for their extended tail; which extends more than one third beyond the tail membranes; most other bats have tails that are completely enclosed within the tail membranes. You can see the free tail clearly in this photo.

Researchers have found the Mexican free-tailed bat can reach speeds up to 100 mph, making it by far the fastest mammal on earth.

Tracy (above) is a Yuma myotis and Davey (below) is a Mexican free-tailed bat. Both Tracy and Davey were were rescued by the SD Humane Society's Project Wildlife.

Tracy and Davey were deemed to be non-releasable by the project veterinarian and both went on to become program ambassadors and help to educate humans about protecting our bat populations. (Photos provided by SD Humane Society)

Bat colonies are typically found in protected locations that are elevated. Human and bats encounters do happen when bats decide to roost in human-designed places. Eaves, barns, garages, bridges, and other comparable locations are favorite roosting places for colonies of bats.The Humane Society shares info on what to do if you have bats on your property: What To Do About Bats

The Yuma myotis below have taken up residence in the eaves along an entry path at a home in Rancho Santa Fe. (photo by John Jones)

5 And Keeping Environments Healthy Super Power

• The majority of bat species are insectivores and can eat their body weight or more in insects each night. Many of the insects they devour are pests of agricultural crops. Scientists estimate that insect-eating bats may save U.S. farmers about $23 billion per year by reducing crop damage and limiting the need for pesticides.

 

• And worldwide, at least 549 plant species either are pollinated or dispersed by bats. Those include many popular food crops ; bananas, mangos, guavas, and cacao (the main ingredient in chocolate). Dispersal is important to maintain healthy, genetically diverse plant populations. And bats can fly long distances, which are necessary in dispersing seeds over large landscapes.

• The two species of local bats, the lesser long-nosed bat (Leptonycteris yerbabuenae), and the Mexican long-tongued bat (Choeronycteris mexicana), primarily forage on nectar and pollen. These species are important pollinators of agaves and large cacti in southwestern North America. 

Click on the video below to see and learn more about the important relationship between agave and the lesser long-nosed bat.

We couldn't finish this article without sharing a little about bat pups (also known as sky puppies).

Bats are slow reproducers; female bats often only produce one offspring per year. Female bats give birth to young while hanging upside down, they then catch and place the young inside their pouches for safety. You can learn all about the world of bat pups; at BatCon. Make sure to check out the video of a bat giving birth!

Debby, a big brown bat pup rescued through Project Wildlife, is receiving milk at feeding time.

Photo by Dick Wilkins- Project Wildlife Volunteer.

We are all in this together and there is no Planet B!

Pacific Mole Crab (aka sand crab)

photo by: Jerry Kirkhart

Its eyes are on long stalks and its  antennae are long enough that it can keep them above the surface even after it has burrowed backwards into the sand. 

The swash zone is the turbulent area where the waves break along the shoreline so you better have some serious adaptions if you want to call it home. The Pacific mole crab (Emerita analoga) is one of the few organisms that lives in that liminal space alternately covered by water as the waves rush in and then air as the water is backwashed. Living in the swash zone is a nomadic lifestyle for mole crabs. They live in colonies and the entire colonies moves up and down the swash zone as the tide shifts.

Take 4 minutes to watch the fascinating video: For Pacific Mole Crabs It's Dig or Die—Deep Look; Get a close up view of how they feed on plankton, and if backwards digging were an Olympic Sport, they would surely take home the gold.

During the reproductive season (February–October), females can produce one clutch of up to 50,000 eggs per month, which take approximately 30 days to develop. Check out this fact sheet for lots more interesting stuff:

The Pacific Mole Crab: Fact Sheet

You can see the female in the photo with her clutch of orange eggs. She was flipped over and she quickly burrowed back into the sand clutching her eggs.

Photo by J. Cannon

Impacts of Plastic Pollution on Pacific Mole Crabs

Unfortunately, the swash zone is also home lots of plastic pollution. A 2020 study found Pacific mole crabs, which are a key species in beach ecosystems, are impacted by microplastics. 

Mole crabs were found to have increased adult mortality and decreased reproductive success when exposed to plastic microfibers. Since Sand crabs eat by filtering small particles from the water, they are considered indicator species because their health reflects the health of the ecosystem. When pollutants affect mole crabs, most other organisms in that ecosystem are also affected—they are prey for birds, mammals and fishes. Read more about the study.

Preserve Calvera has been testing for microfibers in our local creeks. You can read more in our April 2023 Newsletter.