Locating large insects using automated VHF radio telemetry with a multi-antennae array

1. We describe an automated radio telemetry system (ARTS) designed for estimating the location of 0.50g butterflies that was constructed with commercially available materials. Previously described systems were not designed to estimate fine-scale locations of large insects within approximately 200m$^2$ study areas. 2. The ARTS consists of four receiving stations. Each receiving station has four 3-element, directional Yagi antennae (separated by 60\si{\degree}) connected to an automated receiver that records detected power sequentially from each antenna. To develop and evaluate the ARTS performance, four receiving stations were installed in the corners of 4-ha and 6.25-ha square fields with varying heights of vegetative cover. The location of a 0.22g transmitter was estimated with a statistical method implementing both distance- and angle-power relationships. Calibrated model parameters were based on power detected from transmitters at known locations. Using independently collected data, model performance was evaluated based on estimated locations of a georeferenced stationary transmitter, a moving transmitter with a known georeferenced path, and a transmitter attached to a monarch butterfly (\textit{Danaus plexippus}). Estimated locations were calculated as frequently as every 5 seconds, which is at least 12 times greater than the sampling frequency previously reported for tracking insects. 3. When sufficient power data was received, the median estimated locations of a transmitter attached to an investigator's hat were $<$16m from the true location. The median effective radius of the 95\% confidence ellipse was 18.3m for stationary targets and 15.9m for a moving transmitter. Greater error in location estimation was expected when the transmitter was attached to a monarch butterfly due to interference from vegetation and variability in antenna orientation and transmitter height. As such, the median distance between the estimated and true locations was 72m. After applying a correction for the effect of vegetation, median location error was reduced by 12m. 4. While our ARTS has likely reached the limit of current technology, the system is still a substantial methodological advancement for locating butterflies. Our efforts should provide a benchmark as technology improves.

1. 本研究介绍了一款采用商用材料搭建的自动化无线电遥测系统（automated radio telemetry system, ARTS），用于定位体重0.50g的蝴蝶。此前已报道的遥测系统均未针对约200平方米研究区域内大型昆虫的精细位置估算进行设计。
2. 该自动化无线电遥测系统包含4个接收站。每个接收站搭载4副3单元定向八木天线（Yagi antenna，间距为60°），连接至自动接收机，该接收机可依次记录各天线接收到的信号功率。为开发并评估该系统的性能，研究人员将4个接收站分别部署于4公顷、6.25公顷方形样地的四角，样地内植被覆盖高度各不相同。研究采用一种综合距离-功率与角度-功率关系的统计方法，对0.22g发射机的位置进行估算。校准后的模型参数基于已知位置处发射机的接收功率所得。本研究使用独立采集的数据，从三类对象的估算位置出发对模型性能进行评估：一是带有地理坐标的静止发射机，二是沿已知地理参考路径移动的发射机，三是附着于君主斑蝶（*Danaus plexippus*）的发射机。位置估算的频率最高可达每5秒一次，这一采样频率至少比此前报道的昆虫跟踪采样频率高出12倍。
3. 当接收到足够的功率数据时，附着于研究人员帽子上的发射机的估算位置中位数与真实位置的偏差小于16米。针对静止目标的95%置信椭圆的中位有效半径为18.3米，针对移动发射机的该值为15.9米。由于植被干扰、天线朝向与发射机高度的变化，当发射机附着于君主斑蝶时，预计位置估算误差会更大。此时估算位置与真实位置的中位偏差为72米。在针对植被影响进行校正后，中位位置误差降低了12米。
4. 尽管本研究搭建的自动化无线电遥测系统可能已达到当前技术的上限，但该系统仍是蝴蝶定位领域一项重要的方法学进展。随着技术迭代，本研究的工作可为后续研究提供基准参考。