Bird movements at rotor heights measured continuously with vertical radar at a Dutch offshore wind farm

Abstract

Assessing the impacts of avian collisions with wind turbines requires reliable estimates of avian flight intensities and altitudes, to enable accurate estimation of collision rates, avoidance rates and related effects on populations. At sea, obtaining such estimates visually is limited not only by weather conditions but, more importantly, because a high proportion of birds fly at night and at heights above the range of visual observation. We used vertical radar with automated bird‐tracking software to overcome these limitations and obtain data on the magnitude, timing and altitude of local bird movements and seasonal migration measured continuously at a Dutch offshore wind farm. An estimated 1.6 million radar echoes representing individual birds or flocks were recorded crossing the wind farm annually at altitudes between 25 and 115 m (the rotor‐swept zone). The majority of these fluxes consisted of gull species during the day and migrating passerines at night. We demonstrate daily, monthly and seasonal patterns in fluxes at rotor heights and the influence of wind direction on flight intensity. These data are among the first to show the magnitude and variation of low‐altitude flight activity across the North Sea, and are valuable for assessing the consequences of developments such as offshore wind farms for birds.

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

“…2) The Merlin tracking software (DeTect) of the RBR is not always able to differentiate between single birds and small groups of birds. As shown by Fijn et al (), this might result in an underestimation of the MTR by up to 10%. 3) The orientation of the vertically rotating RBR antenna is along the E–W axis, which was logistically the only possibility.…”

High passage rates and different seasonal migration strategies of birds along the lower Texas coast

“…We treated each single observation as an individual record and did not distinguish between single or flock targets due to the unknown number and bird species of radar observations (Mabee et al, 2006). Because of this aspect of radar technology, we acknowledge that it is likely that we underestimated the magnitude of bird migration in our study (Fijn et al, 2015). For our comparison of migration characteristics between diurnal and nocturnal periods we used the onset and end of civil twilight to distinguish between nocturnal and diurnal time periods (Zehnder et al, 2001).…”

The grand challenges of migration ecology that radar aeroecology can help answer

“…Over the past decades, many migratory populations have faced substantial declines, and these have mainly been a consequence of rapid and massive expansions of human structures and activities, habitat alterations and climate change. Migratory animals might be particularly affected as they rely on multiple, distant sites throughout their annual or life‐cycles (Runge et al , ) and changes in any of those sites are fitness‐relevant and may carry over to demographic rates and trends in their populations. There are also several evolutionarily novel factors such as artificial light at night (ALAN), electromagnetic noise, or wind energy installations, which have enormously expanded in recent years and now represent significant and ubiquitous distortions particularly to aerial migrations (Engels et al , Fijn et al , McLaren et al ).…”

“…Yet, what are the research priorities and where are we in providing answers to fundamental questions and societal challenges? Although important advances in answering these questions have been made with individual bio‐logging devices (Kays et al , Wilmers et al ), they can usually only be applied to relatively small numbers of individuals. However, if we are concerned with large‐scale patterns typical of migrations and their long‐term trends, a complementary, macroecology approach might be better suited (Kelly and Horton ).…”