(electromagnetic) dawn chorus

half 5 in the morning and the birds are awake... The electromagnetic dawn chorus is an unexplained phenomenon that occurs most often at sunrise or shortly after, that (with the proper radio equipment) resembles the sound of the birds’ dawn chorus. The electromagnetic dawn chorus is believed to be generated by a Doppler-shifted cyclotron interaction between anisotropic distributions of energetic electrons and ambient background. The dawn chorus occurs when songbirds sing 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 or trying to attract a mate. spring equinox 20th march 2012