Our GPS data loggers start at just 2 grams. The weight increases in very small increments as larger batteries are used. Telemetry Solutions is already producing GPS data loggers in large quantities just for small birds! Since you already know where the birds rest you are probably more interested in their foraging destinations. Our free user interface software will prove extremely useful as you program your bat GPS data loggers to acquire GPS positions at the dates and times that you need them. That prevents using precious battery life at times when the birds are just hanging around.