The Bats Were Hungry

Thursday evening I went on a "bat walk" in Regent's Park. I'd seen a sign posted when I went walking in the park on Monday last: "Bat walk Thursday evening, equipment provided, wear appropriate clothing." I was intrigued. Equipment? Appropriate clothing? I rang the number from the sign and put my name down.

The group assembled at Hanover Gate in the park at 9 o'clock PM. A bookish husband and wife (and their son) from the Bat Conservation Trust arrived to lead the group. The equipment they provided was a bat detector--a black box about the size of an old transistor radio that picks up a bat's echolocation ultrasound emissions.

Our small group of ten waited by the lake until the sun had really gone down. At this time of year the sky remains light in London well past 9 PM. While we waited the bookish man gave us various lectures about bats: the varieties we might see that night, social behavior, feeding habits, etc. All around us insectivorous birds (swifts, swallows) were skimming the surface of the lake in a feeding frenzy. But pretty soon the birds all disappeared and it was time for bats to take center stage.

We moved around the lake to a grove of sturdy old trees and set the bat detectors at 45-47 kHz. Very shortly the detectors started squawking, almost like Geiger counters. The bats were right over our heads in the trees. It seems the first bats to appear in the evening tend to feed under the shade of trees to protect themselves from their natural predators (owls, etc). As the night deepens, the bats feed out in the open.

We ventured out into the open ourselves, down by the lake, and the bats were everywhere. They were swerving and diving all around us. These were all pipistrelle bats whose bodies are about as big as a man's thumb! As small as they are they eat thousands of insects per night of feeding. And these were especially hungry because the night before had been rainy and bats don't fly or eat in the rain. The rain interferes with their echolocation and they can't find food.

By shining the light of a torch (flashlight) along the surface of the lake we were also able to make out a Daubenton's bat. This variety skims the surface of a body of water eating bugs. It's like a natural hovercraft.

After ninety minutes the group headed for the locked gate and were released by a park ranger. I thought this was a fun and unusual way to spend an evening in London!