Fig. 2. Maps of nocturnal bird migration across the Netherlands in spring and autumn, with the 100 km radius circles of the weather radars enclosing the onshore study area. Colors represent seasonal migration passage, converted from the original bird densities. Shaded areas mark grid cells for which over 25% of the input data, prior to filtering, were impacted by ground clutter. Migration passage in these regions may be compromised in either direction: overestimated due to remaining clutter artifacts or underestimated where terrain features partially obstruct the radar’s lower scanning angles.
Fig. 1. Flight altitude distributions (in m above sea level (asl)) of nocturnal bird migration for both Dutch weather radars at a coastal Den Helder and inland site Herwijnen. Bar length denotes the proportion of migration within the respective altitude range (50 m vertical resolution). Donut charts aggregate this further to coarser 200-m classes and display the proportion of migration occurring above 1000 m (patterned). Red highlights indicate the altitude range of onshore energy infrastructure in the Netherlands, which is generally present in the lowest 200 m of the atmosphere. Donut chart proportions do not sum to 100% due to rounding. The small inset map of the Netherlands shows the locations of both radars (solid dots) and the surrounding areas up to 35 km (circles) from which altitude distributions are aggregated.
Fig. 3. a, c Observed combinations of migration passage and mean wind power density, a measure of wind power potential, in North-Holland. Red circles represent average values for candidate sites and their size reflects the relative candidate site area. The grid reflects binned values of migration and wind power density, with color shading indicating the type of combination: orange = high migration passage, blue = high wind power density, dark browns and blues = both high. White lines indicate averages for wind power density and seasonal migration passage. b Spatial distribution of autumn migration (orange hues) and wind energy (blue hues) in North-Holland. Candidate wind energy sites are shown in bright red. The highest and lowest autumn migration passage sites are linked to their positions in a and c, emphasizing large differences between sites in autumn, but not in spring. Shaded areas mark grid cells for which over 25% of the input data, prior to filtering, were impacted by ground clutter. Migration passage in these regions may be compromised in either direction: overestimated due to remaining clutter artifacts or underestimated where terrain features partially obstruct the radar’s lower scanning angles.
To reduce negative impacts of #renewables (eg #windenergy) on migrating birds, we need to know *where* and how *high* they fly. Using weather radar, we mapped 6yrs of nocturnal migration over the Netherlands, revealing patterns we can use to avoid and minimize impacts:
doi.org/10.1016/j.je... 🧪🪶
