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Nocturnal migration can be monitored using weather radar data, [40] allowing ornithologists to estimate the number of birds migrating on a given night, and the direction of the migration. [41] Future research includes the automatic detection and identification of nocturnally calling migrant birds.
"80% of our migratory birds here in North America are actually migrating at night," he said. "A large impact that humans actually have on birds during migration is with the light that we produce ...
Coot species that migrate do so at night. The American coot has been observed rarely in Britain and Ireland, while the Eurasian coot is found across Asia, Australia and parts of Africa. In southern Louisiana, the coot is referred to by the French name "poule d'eau", which translates into English as "water hen".
The Arctic tern has the longest migration journey of any bird: it flies from its Arctic breeding grounds to the Antarctic and back again each year, a distance of at least 19,000 km (12,000 mi), giving it two summers every year. [19] Bird migration is controlled primarily by day length, signalled by hormonal changes in the bird's body. [20]
There are many birds that are active nocturnally. Some, like owls and nighthawks, are predominantly nocturnal whereas others do specific tasks, like migrating, nocturnally. North Island brown kiwi, Apteryx mantelli [1] Black-crowned night heron, Nycticorax nycticorax [1] Short-eared owl, Asio flammeus [1] Long-eared owl, Asio otus [1]
Most birds winter within the southern parts of the breeding range, but smaller numbers cross the Mediterranean into Africa or travel over the mountains of Malaysia into Southeast Asia. Kingfishers migrate mainly at night, and some Siberian breeders must travel at least 3,000 km (1,900 mi) between the breeding sites and the wintering areas. [7]
Species that live in the far north, such as the European nightjar or the common nighthawk, migrate southward with the onset of winter. Geolocators placed on European nightjars in southern England found they wintered in the south of the Democratic Republic of the Congo. [9] Other species make shorter migrations. [8]
Mortality on wintering grounds: Unreasonably cold temperatures on the wintering grounds kills thousands of birds, resulting in 30-90% population declines of migratory birds. For example, between 27000 and 62000 ducks, mostly tufted duck and common pochard , starved to death during a very cold winter in March 1986.