Radar image from 2007/2008. The image shows a lot of stationary reflectivity from the ground which is not due to birds. At 23:30 a few passing rain showers can be seen. At midnight the image clearly changes and very high reflectivity (orange and red colors) due to birds is seen.
Radar image from 2008/2009. At midnight a sudden increase in reflectivity is visible (orange and red).
Radar image from 2009/2010. The upper half of this image shows reflectivity throughout the night due to a band of light precipitation. At midnight a sudden increase in reflectivity is visible (orange and red) due to birds in the air.
Radar image from 2010/2011. In addition to reflectivity due to rain throughout the night, at midnight a sudden increase in reflectivity is visible (orange and red) due to birds in the air.
Radar image of 2011/2012 (De Bilt).
Radar image of 2011/2012 (Den Helder).
Radar measurements of De Bilt, 2012/2013.
Radar measurements of Den Helder, 2012/2013.
Live radar measurements of De Bilt, 2013/2014.
Live radar measurements of Den Helder, 2013/2014.
Birds flee en mass from fireworks on New Year's Eve
Every year thousands of waterfowl take flight right after midnight as citizens shoot their fireworks. Researchers from the University of Amsterdam, the Dutch and Belgian weather services and the Royal Netherlands Air Force conclude this based on measurements with weather radars in the Netherlands and Belgium. While normally used to observe rain, these radars can also detect flying birds.
On New Year’s Eve the radars detected thousands of birds in the air up to altitudes of 500 m. High densities of birds are measured in the radar air space for 45 minutes after fireworks are first lit. The highest densities were observed over grasslands and wetlands, including nature conservation sites, where thousands of waterfowl rest and feed in the winter.
The animations show images of radar reflectivity within a 40 km radius from the radar in De Bilt. Reflectivity abruptly increases every year at midnight as birds take off in great numbers. Dark red represents a high radar reflectivity, which is correlated with a large density of flying birds. The highest density of birds in the air at one time may reach 1000 birds/km2. If it rains, birds can be invisible because the reflectivity is dominated by the rain. Large rivers and important water bodies are shown in blue.
Researchers from the University of Amsterdam, KNMI and the Royal Netherlands Air Force have been studying the response of birds to fireworks on New Year’s Eve using weather radar for several years. In 2012/2013 the Belgian Meteorological Institute joined this effort. More information can be found in the scientific article published in Behavioral Ecology in 2011: "Birds Flee en mass from New Year's Eve fireworks".