The acoustic communication and echolocation of bats are among the most sophisticated and technically impressive sensory capabilities in the animal world. The study of bats is important to gain insight into these capabilities as well as to understand the roles of bats as predators of agricultural pests and vectors of infectious disease. Specifically, analysis of the acoustic signals used by bats for foraging and communication is necessary to understand their community structure, hunting patterns, and the signal processing underlying their capabilities. However, efforts to study bat calls in natural settings have been limited by the constraints imposed by ground-based recording equipment. Because of their small body sizes most bats are incapable of carrying existing ultrasonic recording instruments. Therefore, all studies to date have been conducted either in artificial laboratory conditions with fixed recording equipment, or in the wild with ground-based, typically stationary, recording equipment. Both methods have a variety of serious shortcomings. Ultrasound signals are context-specific and vary rapidly and over short distances, so a fixed recording device will not capture the same signals observed by a bat. Laboratory conditions cannot mimic the complex natural environment. With the use of ground-based recordings it usually is not possible to separate the calls made by individual bats. The echoes reflected from targeted insects often are too faint to be detected by ground-based recording equipment. As a result, the information obtainable by ground-based equipment is necessarily incomplete. With recent advances in electronics technology, a wide variety of miniaturized sensors have become possible. This project will include the development of miniaturized ultrasonic recording devices to be mounted on bats for recording calls and echoes during flight. The final design will utilize a custom integrated circuit (IC) to achieve a total system weight under 1 g.
This project will result in an acoustic monitoring device unlike any existing instrument. By reducing the distance between the bat and the transducer from a few 10's of meters to a few centimeters, the instrumentation developed in this project will realize an improvement in signal quality of several orders of magnitude compared to existing ground-based recording techniques. Furthermore, recordings of more distant bats that are currently infeasible due to signal attenuation will be made practical with the proposed instrument. A bat-mounted recorder will also enable separation of signals from individual bats and the ability to follow an individual bat over a significant distance. Additionally, the proposed research will advance the design of ultra-low-power wireless instrumentation and integrated circuit design. This project offers the potential to introduce a breakthrough in methods for bat research. The knowledge gained through the use of the proposed instrument will provide important insights into communication among bats that are relevant to the role of bats as predators of agricultural pests and to public health concerns regarding bats' role as disease vectors. It will also contribute to the understanding of bats' ultrasonic sensing capacities. The instrumentation developed in this project will also be useful for a wide variety of other scientific investigations, such as the study of song learning in songbirds or language acquisition in human infants. The interdisciplinary nature of the project will provide an opportunity for graduate and undergraduate students to work at the intersection of biology and electronics. The integration of the proposed circuits into a complete recording system will provide valuable practical experience in working with complex electronic systems-on-chip.
