The dawn chorus is the outbreak of birdsong at the start of a new day. In temperate countries this is most noticeable in spring when the birds are either defending a breeding territory, trying to attract a mate or calling in the flock. In a given location it is common for different species to do their dawn singing at different times.
In some territories where bird life is extensive and birds are vocal, the sound of a dawn chorus may make it difficult for humans to sleep in the early morning.[1] [2] [3]
In a 2007 study of the Ecuadorian forest, it was determined that birds perching higher in the trees and birds with larger eyes tend to sing first.[4] This may be due to differences in the amount of light perceived by the birds.[4]
Moller used a play-back technique to investigate the effects of singing by the black wheatear (Oenanthe leucura) on the behaviour of both conspecifics and heterospecifics. It was found that singing increased in both groups in response to the wheatear. Moller suggested the dawn (and dusk) chorus of bird song may be augmented by social facilitation due to the singing of conspecifics as well as heterospecifics.[5]
An annual International Dawn Chorus Day is held on the first Sunday in May[6] when the public are encouraged to rise early to listen to bird song at organised events. The first ever was held at Moseley Bog in Birmingham, England, in 1987, organized by the Urban Wildlife Trust (now The Wildlife Trust for Birmingham and the Black Country).
Early explorers and European settlers noted that the New Zealand forest had a loud dawn chorus. The dawn chorus is no longer as loud as it once was, owing to extensive loss of forests, the introduction of bird predators and competing species such as wasps. The bellbird and the tūī are two of the birds that would have formed part of the dawn chorus since they have a vocal and melodious call.
In the UK the dawn chorus may begin as early as 3am in early summer.
The dawn chorus may also be heard in the United States.