Tuesday, September 8, 2009
The result: evidence that suggests that male bats sing songs with distinguishable syllables and phrases to attract females, and in some cases, to warn other males to stay away. The paper written about the study was published in PLOS One.
The research was a collaboration of the owner of the barn, Barbara Schmidt-French of Bat Conservation International; George Pollak, a neurobiologist at The University of Texas at Austin; and Kirsten Bohn and Mike Smotherman, biologists at Texas A&M University.
Pollak explains how the project developed:
“Barbara French had a colony of about 70 Mexican free-tailed bats that she maintained in a barn in her backyard. Barbara loves her bats and ‘hung out’ with them for several hours a day, every day for several years. She knows them very well.
“Several years ago she came to my office and told me about the complex social behaviors these bats exhibit and that specific and different vocalizations are emitted during each behavior.”
Schmidt-French could hear just the sounds the bats made, but the higher frequency range of their communications was out of reach to human ears.
“She did not have the electronic equipment needed to record and analyze the sounds, but I did,” Pollak said. “So we began a collaboration to evaluate the various communication calls that the bats were emitting in Barbara’s barn.”
Here’s the description of the equipment presented in their paper:
The equipment included a Brüel and Kjær type 4939 microphone and a custom-made amplifier. A custom-made digital time expander recorded a maximum of one second that was expanded to 10 seconds at 16 bits and was played onto a computer at a sample rate of 44.1 kHz. In 2005 and 2006, calls were recorded directly onto a computer at a sample rate of 300 kHz using a high-speed data acquisition card and Avisoft recorder. Both systems allowed recordings up to 150 kHz, well above the frequency content of vocalizations.
What that means for those of us who aren’t audiophiles is that the researchers used sophisticated equipment that enabled them to capture and analyze the bat communications to within a millimeter of its life.
All that data needed to be analyzed.
Pollak that’s where statistics came in. It was Bohn, who goes by Kisi, who took the project to “an entirely new level both in terms of specificity and sophistication.”
“Kisi is not only a first rate behaviorist and evolutionary biologist, she is an expert statistician, and the dissection of the features of the calls and songs required sophisticated statistical analyses,” Pollak said.
“What she did is to not only confirm that the songs are composed of elements or notes that have an orderly combination, but she showed what the rules are that determine those combinations,” he said. “More specifically, she showed the rules that govern the sequence of notes in the courtship song and that the same rules are followed in two disparate populations, one population in Barbara’s barn in Austin and the other a wild population in College Station.”
Pollak is quick to say that the findings suggest, but do not prove, that the rules or syntax that are expressed in these calls are probably hard wired somewhere in the brain, rather than being learned from early experience.