Comparison of bird migration in a radar wind profiler and a dedicated bird radar

Abstract

Various types of radar systems are increasingly being used to monitor aerial biodiversity. Each of these types has different detection capabilities and sensitivities to environmental conditions, which affect the quantity and quality of the measured objects of interest. Radar wind profilers have long been known to detect birds, but their use in ornithology has remained limited, largely because of biologists' unfamiliarity with these systems. Although the potential of radar wind profilers for quantitative bird monitoring has been illustrated with time series of raw data, a comparison with a similar radar system more established in biology is missing. Here, we compare nocturnal bird migration patterns observed by a radar wind profiler during October 2019 and April 2021 with those from a dedicated bird radar BirdScan MR1. The systems were located 50 km apart with an altitudinal difference of about 850 m. The nightly migration intensities measured with both systems were highly correlated in both spring and autumn (Pearson correlation coefficient ≈ 0.8, P < 0.001), but estimated traffic measured by the radar wind profiler was on average five times higher in spring and nine times higher in autumn. Low ratios of the migration traffic rates of the Birdscan MR1 to those of the radar wind profiler occurred primarily in clear conditions. In both radar systems, migration occurred at significantly higher altitudes in spring than in autumn. Discrepancies in absolute numbers between both systems are likely due to both system‐inherent and external environmental and topographical factors, but also different quantification approaches. These findings support the capacity of radar wind profilers for aerial biomonitoring, independent of environmental conditions, and open up further avenues for studying the impact of weather on bird migration at detailed temporal and altitudinal scales.

Evaluating the potential of bioacoustics in avian migration research by citizen science and weather radar observations

“…Seasonal differences in flight altitudes are a known phenomenon (e.g. [47,51]) and have also been observed in the Baltic Sea [52]. Higher flight altitudes in spring as found in these studies could explain the silence in spring because birds would evade being recorded.…”

Continental-scale patterns in diel flight timing of high-altitude migratory insects

“…We used a network of BirdScan MR1 (software v1.6.0.12) 25 kW X-band (9.4 GHz, 3.2 cm wavelength) pulse radars with an optionally rotating Horn antenna (nominal beam width at −3 dB is approx. 17.5°) [ 35 , 36 ] to measure aerial insect movements. The Birdscan MR1 radar can be operated in different modes (e.g.…”

Monitoring aerial insect biodiversity: a radar perspective

“…Although a variety of other radar types exists, e.g. frequency-modulated continuous wave radar [24], cloud radar [25,26], wind profiler [27] and airborne doppler radar [28], these have only sporadically been employed in insect studies and are therefore not discussed further. Small-scale (vertical-looking) biological radars use fixed-beam sampling with a beam angle of only a few degrees, which increases beam intensity, detectability of weakly reflecting targets, spatial resolution and altitudinal range (figure 2).…”

“…Although a variety of other radar types exists, e.g. frequency-modulated continuous wave radar [ 24 ], cloud radar [ 25 , 26 ], wind profiler [ 27 ] and airborne doppler radar [ 28 ], these have only sporadically been employed in insect studies and are therefore not discussed further.…”

“…Small-scale (vertical-looking) biological radars use fixed-beam sampling with a beam angle of only a few degrees, which increases beam intensity, detectability of weakly reflecting targets, spatial resolution and altitudinal range ( figure 2 ). While the beam could be pointed in any direction, in practice it is always pointed upwards, albeit sometimes with a small angular offset [ 17 , 22 , 27 , 29 ]. These radars record the movements of single individuals passing through the radar beam and the returned echo contains information on an individual's trajectory (height, displacement speed, alignment), wing beat frequency and radar cross section [ 17 ].…”