Well as luck would have it, I managed to convince Drew to let me tag along with him on more bat expeditions.  On January 29^th, we met at Mission Gorge Regional Park for a roost exit survey at an old quarry.  The area was known in the past to function as a roost for pocketed free-tailed bats [Nyctinomops femorosaccus], and Drew wanted to confirm that this was still the case.  Shortly after sunset, the bats (later confirmed as pocketed free-tailed bats) began to emerge and fly down to forage over the riparian zone just adjacent to their roosting site.  The bat detector chirped and squawked as it recorded the bat calls, and great horned owls (Bubo virginianus), common poorwills (Phalaenoptilus nuttallii), and Pacific tree frogs (Pseudacris regilla) added to the cacophony.

After approximately an hour of the relatively unorganized calls of the free-tailed bats, we heard a different sound.  An organized, even-pulsed bat call materialized very near to us, heading down the riparian area.  Drew later identified this as a western mastiff bat (Eumops perotis californicus), and as we did not hear it approaching from a distance (rather, it seemed to just “materialize”) we suspect it may also be roosting at the quarry, not just foraging in the area.

Photo Credit: By Kjfmartin (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons