Radar wind profilers and avian migration: a qualitative and quantitative assessment verified by thermal imaging and moon watching

Abstract

Summary Radars of various types have been used in ornithological research for about 70 years. However, the potential of radar wind profiler (RWP) as a tool for biological purposes remains poorly understood. The aim of this study is to assess the suitability of RWP for ornithological research questions. A 1290 MHz RWP at the south‐eastern coast of the Bay of Biscay has been known to exhibit seasonally occurring nocturnal signals attributed to migrating birds. As a first step to verify the origin of these seasonal patterns, historical radar data from 2010 to 2012 were analysed, and both bird patterns and temporal occurrence were identified in RWP data at different levels of the signal processing. A thermal‐imaging (TI) camera in conjunction with moon watching was used as verification systems at the radar site to confirm the ornithological origin of the radar echoes. The simultaneous data on spring migration served as a basis for the identification of biological signatures (qualitative parameters) on time‐series level (raw data) and to derive quantitative migration parameters (flight altitude, migration traffic rates) thereof. Finally, the quantitative measurements of the TI camera and the radar were compared considering meteorological conditions. The approach allowed identifying reproducible criteria based on time series to calculate migration traffic rates and altitudinal flight distribution. General flight directions were only available in the final wind data. In clear weather conditions, the calibration methods coincided well with the wind profiler data. Findings show that wind profiler raw data offer reliable information on migration intensity, flight altitudes and flight directions in a variety of meteorological conditions. The method presented can be applied as a complement to present efforts to use weather radars for large‐scale bird monitoring. Furthermore, it is also interesting for the meteorological community to refine signal‐processing methods.

Using infrared thermography to detect night-roosting birds

“…Consistent with this expectation, Weisshaupt et al. () found that long‐range IR detectability decreased considerably with precipitation and cloud cover when compared to radar detections.…”

“…, Weisshaupt et al. ) and quantifying detection rates of white‐tailed deer ( Odocoileus virginianus ) through simultaneous spotlight and IR surveys (Collier et al. ).…”

“…Precipitation has been demonstrated to negatively affect thermal sensitivity (e.g., Weisshaupt et al. ). However, detection distance in our study was limited to 10 m and, under these conditions, animal heat signatures could still be distinguished from their surroundings during periods of intermittent light rain, albeit with reduced clarity.…”

Cross‐calibration of different radar systems for monitoring nocturnal bird migration across Europe and the Near East

“…Vertical bird profiles were extracted every 5 min from 133 m up to 2000 m a.g.l. Details on bird extraction procedure from this radar system and the calculation of the MTRs adapted to the respective data collection mode are given in Weisshaupt et al (2017). This radar is referred to as radar wind profiler (RWP).…”

“…Therefore, a reason for the much lower MTR might be due to a reduced detection probability for small passerines with distance, reinforced by the relatively long wave-length. For the RWP a first inventory of features and echo strengths has been provided for various targets (Weisshaupt 2015, Weisshaupt et al 2017. However, echoes included in the MTR calculations had to be close to the beam center to be recognized as birds (Weisshaupt et al 2017).…”