A discovery of the Bat Project was the use of stainless steel ball chain as a bat necklace. We strung a numbered aluminum bird band on the necklace. Now that is the world standard. Everybody uses necklaces for marking bats. Previously bats had been marked with bird bands on their forearms. That usually, or at least often, proved lethal because the band was right by the bat's nose as it hung upside down in sleeping position. It chewed on the band and irritated and often infected the forearm. I've caught bats that other people had banded years before, that were still oozing pus and blood from under the band. I said to myself, "I'm never going to do a project with live bats if I can't find some better way to mark them!" So I spent about a year trying everything until I finally came up with necklacing.
We now are experimenting with transponders on bats, which we implant with a syringe under the skin in the middle of the back where the bat can't reach it. This is a passive numbered microchip. We use a reader to get the number back. There are no moving parts so the transponder should easily last the life of the bat. Of course, we must catch the bat once to put the transponder in it, but thereafter we have only to get close enough to it so that we can read the microchip. We've invented, with the help of a company in Idaho, a reader that we can use at the entrances of bat roosts. The comings and goings of all the bats are read off into a computer.
Here's a necklaced bat. I've caught nine-year-old necklaced bats. The necklaces looked like they had just been put on and the bats were healthy and still reproducing. In the Bat Project, my original intent was to go through a generation of bats, whatever that turned out to be. After the first year, we could estimate mathematically for Artibeus jamaicensis, which made up two-thirds of all the bats we caught, that its life expectancy was about two years and that the ultimate longevity should be nine or ten years. So among 35,000 marked bats, we caught two nine-year-old bats, just right in that mathematical window.
My Bat Project was always popular with people who had never been in the jungle at night. Taking them along gave me chances to lecture about bats.