The Call of the Bats

February 15, 2017 Posted by: Stephanie Root
Cabrillo National Monument, located in San Diego, CA, is a small 165 acre park that is located on the tip of the Point Loma peninsula. Though a small park in size, Cabrillo National Monument exhibits a diverse landscape of terrestrial and marine biota. Biologists with the Monument and the San Diego Natural History Museum have teamed up to monitor and inventory bat species. Specifically, setting up a protocol to record echolocation calls on a seasonal basis as well as looking for any signs of the Mexican long-tongued bat (Choeronyteris mexicana), which is a suspected pollinator of the Shaw’s agave (Agave shawii), a rare plant of management concern.

Bat echolocation calls are recorded on a small device called an Anabat. This device records any ultrasonic call inaudible to the human ear, and saves it into graphical form (Fig 1). Bat species have unique call frequencies and shapes that an experienced bat biologist can then interpret and determine species.

Initial results show that more than triple the amount of calls recorded were in the fall compared to any other season, which may mean that bats are using the peninsula as a migratory stopover in the fall. Although the Mexican long-tongued bat was not detected during these surveys, the first detection of the Yuma myotis (Myotis yumanensis) was recorded, along with nine other species already known to use the peninsula. 

Sonogram of a Mexican Free-tail bat call

Figure 1. Example sonogram of a Mexican free-tailed bat (Tadarida brasiliensis) call. Calls that are slanted are “search phase” calls;  more vertical and closer together indicate a “terminal buzz,” indicating that this bat is in pursuit of an insect or in close proximity to some sort of obstacle it needs to navigate.  Note that the duration of this particular sonogram is under 1 second!

Bats, Natural Resources

Last updated: February 15, 2017

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