A lot of people are interested in the bats that we have in the Los Angeles area. Bats in LA. That's a good thing, because bats need friends. Bats provide a great service by eating tons of insects. But not everything you see with pointy wings flying at dawn or dusk is a bat.
I recently had a comment from a reader asking about groups of 20-30 bats flying over the Los Angeles River in the Burbank area early in the morning. An observant eye can frequently see nature attracted to the Los Angeles River as you make your slow commute on the Ventura Freeway. I've seen these wheeling silhouettes as well, but probably what this traveler saw were birds and not bats.
Bats typically return to their roosts before dawn. Seldom do you see our local bat species in a group unless it is right as they are emerging from their roosting location in the evening.
At specific times of the year when there are insect blooms along the river, you can see swallows or swifts in groups flying quickly over the river catching insects. These small birds can look similar to bats. Both have narrow wings that help them maneuver quickly so they can catch insects on the wing. Both are dark in silhouette and some swallows and swifts have minimal tails that may make them appear batlike.
But if you look closely you will see a difference. Bats typically have a faster wing beat and seldom glide. Swallows and swifts on the other hand will glide in between wing beats. These birds frequently are seen in flocks ranging from 10 to 1,000s of individuals. One evening along the banks of Utah Lake just south of Provo, we watched hundreds of thousands of swallows feeding on swarming insects just before a storm. I've never seen so many birds in one place in my life.
These two animals bats and swallows (or swifts) are filling a similar niche in the ecosystem; they are flying predators feeding on small flying insects. And they share the workload, bats at night and the birds during the day. Occasionally, when the insects are plentiful and the weather is just right the two shifts will cross and you may see the furry and the feathered creatures sharing the sky. Both are doing their best to reduce the numbers of mosquitoes along our river and around our neighborhoods. All they ask in return is habitat to roost and nest in and insects that haven't been poisoned. Birds and bats need you to be their friends.
Swallows and swifts you are most likely to see in the Los Angeles area:
white-throated swift, chimney swift,Vaux's swift, barn swallow, cliff swallow, northern rough-winged swallow, violet-green swallow and tree swallow
For more about these bird species check out Cornell University's About Birds website: http://www.allaboutbirds.org/guide/search