Meeting Abstract
S3-1.2 Friday, Jan. 4 Bats and Angel Rings: Quantifying Flight Behavior and Colony Dynamics using NEXRAD Doppler Radar Data HORN, Jason, W.*; KUNZ, Thomas, H.; Boston University; Boston University jhorn@bu.edu
In 1957, the U.S. government built the first national network of radar systems for weather surveillance. Radar operators soon noticed echoes on their displays that did not behave like weather patterns, including expanding ring-like shapes they called angels. These echoes were caused by high-flying insects, bird migrations, and large colonies of bats emerging from roosts to feed. Modern WSR-88D NEXRAD weather radar stations provide data from which detailed images of bat emergences can be produced and flight behavior of groups of bats can be investigated. Large cave and bridge colonies of Brazilian free-tailed bats (Tadarida brasiliensis) in south-central Texas are clearly imaged by three local WRD88-D Doppler RADAR stations. In this study, we used NEXRAD reflectivity and radial velocity images to examine colony size, direction of movement, speed of dispersion, and altitude gradients of bats from these colonies during the hours after evening emergence. Base reflectivity clear-air mode level II images were geo-referenced and compiled in a GIS along with colony locations and landscape features. Temporal sequences of images were filtered for bat activity and spatial means and total reflectivity were calculated. These measures were used to compute directional vectors and compare emergence behavior using circular statistical models. Relative colony size and inter-annual changes were also measured. Our results indicate that multiple factors play a role in nightly flight and dispersal behavior, and that NEXRAD data can be a useful tool for monitoring the nightly behavior of large bat colonies and seasonal changes in these populations. Understanding the distribution of a large regional bat population on a landscape scale has important implications for agricultural pest management and conservation efforts.
