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Aflockalypse No: Why do birds die in large numbers?

Updated Thursday, 13th January 2011

Some observers have taken the reports of mass bird deaths as a sign of terrible things about to happen. Patricia Ash explains why the truth, though grim, might be less apocalyptic.

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In winter 2010-11 a spate of reports of mass mortalities of flocking birds in Europe and America led to claims of an apocalypse for birds. The reports included 3- 5,000 dead red-winged blackbirds found in Beebe in Arkansas on New Years day.


Firework celebrations in Beebe on New Years Eve included commercial fireworks causing exceptionally loud booms. The birds panicked, flying at speed from their roosting site, colliding with buildings, cars, road signs and the road.

Post-mortem examinations revealed trauma injuries to the birds’ breasts and wings.

Red winged blackbirds have poor night vision so would not have spotted obstacles. However, some local people suggested the birds were poisoned as they are regarded as pests.

Pesticides are used to kill flocks of birds in some countries. In January 2009, about 5 000 dead and dying European starling were found in Griggstown, New Jersey.

European starlings were brought to the USA in 1890, and are regarded as pests as they eat and foul grain put out on farms for livestock.

The starlings were killed by the US Department of Agriculture, using a 'bird-specific' pesticide, DRC-1339, added to bait on a local farm plagued by the birds.

The lights of tall buildings can disorientate flocks of migrating birds, leading to collisions with the windows and vast numbers of deaths, estimated as a million per year in the USA alone. Some cities, including San Francisco, are turning off night-time lighting in tall buildings, which has the added benefit of conserving energy.

A flock of starlings Creative commons image Icon ETGeek (Eric) under CC-BY-NC-ND licence under Creative-Commons license
The heart of the problem? A flock of European starlings

Why do birds form huge flocks and so become vulnerable to mass mortality events?

The advantages of flocking include protection from predators and finding food, especially in winter. A vast mass of birds in flight confuses hawks and eagles. Many pairs of eyes in a flock increase the likelihood of spotting food and predators. Roosting together at night also offers protection.

Nevertheless, both natural factors and human activities cause mass mortalities. Mass bird deaths can be caused by disease and parasites – prolonged cold snaps in winter are lethal for birds, especially small species like blue tits and sparrows. Nevertheless, human activities are increasing the incidence of mass mortality significantly.

Further reading

Fireworks likely cause of massive Ark. bird kill
Massed bird deaths cause alarm in Central New Jersey community
Italian turtle doves found dead
Golden gate Audubon society Lights out for birds

Want to know more?

Why not consider getting to know the natural sciences with a course from The Open University?





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