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An international team of researchers based in the Netherlands used weather radars to monitor the movements of wild birds on New Year's Eve. Radar data revealed that tens of thousands of birds explode into flight promptly at midnight when public fireworks shows begin. The panicked birds reached altitudes of 500 metres where they flew in dense flocks for 45 minutes. The highest flock densities were detected over grasslands and wetlands, and over conservation sites, which are the wintering homes where many tens of thousands of waterfowl, wading and shorebirds, and seabirds rest and feed.
How well do birds tolerate fireworks?
Although people enjoy the colourful flashing lights and loud explosions created by fireworks, almost nothing is known about how wild birds and other wildlife respond to such bizarre nighttime extravaganzas. Previous studies revealed that terrestrial and marine animals respond fearfully to a wide variety of disturbances caused or influenced by humans, such as low-flying aircraft and drones, motor boats, hunting, noise, and even just the mere presence of humans (doi:10.2307/3809202).
Although the Netherlands is a civilised nation, the public is allowed to light their own fireworks on New Year’s Eve, a practice that they enthusiastically seize on a massive scale nearly everywhere in the country. The amount of fireworks consumed annually in the Netherlands alone is estimated to be 10.8 million kilograms (or 23.8 million pounds, which is roughly the same mass as three Saturn V rockets) (free PDF).
In the Netherlands, recreational fireworks can be legally detonated during a four-hour period of time between 10:00 pm on 31 December until 2:00 am on 1 January -- although most are lit during the first 30 minutes after midnight. Additionally, the Netherlands is densely populated, so wildlife conservation areas are typically located close to inhabited areas, where large numbers of birds concentrate.
How to monitor flying birds in the middle of the night?
Since it is nearly impossible to observe birds in the middle of the night, an interdisciplinary team of researchers from the University of Amsterdam, the Royal Netherlands Air Force, and the Royal Netherlands Meteorological Institute used a weather radar to quantify where and when wild birds were disturbed by large-scale fireworks shows held on three consecutive New Year’s Eves from 2008 through 2010. Although this radar was designed to monitor rain and other weather conditions, it could also detect flying birds.
The radar was located 44 metres above sea level in De Bilt, the Netherlands (central red spot, Figure 1). The radar monitored echoes created by flying birds at 5 minute intervals, in various altitude bands within a 25 kilometre (15.5 mile) radius.
Figure 1. Radar images from The Netherlands showing birds scattering when fireworks are set off at... [+]
As you can see, almost no birds were in flight immediately before before midnight on New Year’s Eve. But only a few minutes after midnight, when fireworks were being lit in inhabited areas all over the country, massive movements -- one could say "explosive" movements -- of wild birds were detected. The areas with the greatest radar reflectivity (indicating the greatest density of flying birds) were seen over lakes, wetlands, and river floodplains (blue lines) -- many of which are designated Natura 2000 sites, which are protected as breeding and resting sites for rare and threatened species.
Based on annual winter bird censuses conducted within the radar area, the researchers assumed that most birds present during this time period were large waterfowl -- mostly ducks and geese. To identify relative numbers of passerines:ducks:geese, the researchers estimated the birds' relative body volume by calculating the body area-to-volume as a sphere. Based on their calculations from radar density measurements, the research team estimated that the highest density of birds in the air at the same time may reach 1000 birds/km2.
"It is estimated that hundreds of thousands of birds take flight, just within a 40 kilometre radius of where the radar was taking measurements", said the study's first author, Judy Shamoun-Baranes, who is an Assistant Professor in the Institute for Biodiversity and Ecosystem Dynamics at the University of Amsterdam, in a press release.
"If we consider the entire country using this statistic, millions of birds could be affected. These figures are quite staggering, especially when considering that birds are disturbed from areas that are otherwise designated for conservation of the species, especially during the winter and migration season", said Professor Shamoun-Baranes.
"This phenomenon has also been observed in Belgium, so this issue is clearly not isolated to the area where this particular study took place."
How high did the birds fly and how long did they stay aloft?
Although the research team's time series of radar density measurements from several days and nights before and after New Year's eve showed short intervals of bird movements (Figure 2), these were dwarfed by the very abrupt and explosive increase in density beginning on 1 January at 00:05, as recorded for each year of the study. This density of flying birds reached a maximum between 00:15 and 00:25, with the majority of birds in flight for about 45 minutes (Figure 2d):
Figure 2. Time series of bird movements over Loosdrechtse Plassen. VIR (square centimeter/square... [+]
The radar revealed that the birds rapidly flew up to an altitude of approximately 500 m (1640 feet; Figure 2e) or higher, and then slowly descended -- a pattern that was also seen over other lakes and wetlands in the radar area.
"These altitudes far exceed any these birds would usually reach during local flights, and are in fact comparable to flight altitudes measured during migration", said Professor Shamoun-Baranes.
What happens to hundreds of thousands of panicked birds flying in the dark?
Like humans, birds cannot see very well in the dark (unless, of course, they are owls). This means that, similar to a human stampede trying to escape from a dark and crowded theatre or concert hall, panicked wild birds will crash into power lines, automobiles, buildings, trees, and even each other, especially on cloudy or moonless nights. As with a human stampede, mid-air bird collisions can result in serious injury or death, particularly since birds fly much much faster than a human can possibly run, and because birds fall from the sky after an impact, which can easily render a survivable injury into a mortality.
"The observations in the Netherlands are perhaps extreme due to the high concentrations of birds found in waterbodies in the winter and the close proximity of human activity", said Professor Shamoun-Baranes.
But as people claim more and more wild lands for their own uses, birds and wildlife are concentrated into smaller and smaller areas that are in closer proximity to humans, so more tragedies such as these will occur.
And the fact is that, year after year, somewhere in the world, people are greeted by the chilling sight of dead and dying wild birds falling from the sky on the first day of the New Year, in the aftermath of fireworks displays.
Terrified Birds Flee En Masse From Fireworks | @GrrlScientist
Source:
Judy Shamoun-Baranes, Adriaan M. Dokter, Hans van Gasteren, E. Emiel van Loon, Hidde Leijnse, and Willem Bouten (2011). Birds flee en mass from New Year’s Eve fireworks, Behavioral Ecology, 22:1173–1177 | doi:10.1093/beheco/arr102
Also cited:
Luc Belanger and Jean Bedard (1989). Responses of Staging Greater Snow Geese to Human Disturbance, Journal of Wildlife Management, 53(3):713 | doi:10.2307/3809202
van der Maas CWM, Coenen PWHG, Zijlema J, Baas K, van den Berghe G, van den Born GJ, Brandt AT, Guis B, Geilenkirchen G, te Molder R, et al. (2012). Greenhouse gas emissions in the Netherlands 1990- 2012. National Inventory Report 2012. Bilthoven (The Netherlands): Netherlands Environmental Assessment Agency (PBL). (free PDF).
