Ambient light energy intensity as a trigger for the dawn chorus: Patterns in five common eastern Australian bird species

Abstract

The timing of the morning twilight commencement of bird song has been linked to mating, stores of food energy or territorial declarations, and is known to follow a structured, spaced order to avoid signal interference. The timing of vocalisations has been widely studied and varies with ambient and broader environmental variables, including moonlight and cloud cover. In this study, the commencement of morning song for five common species (Masked Lapwing Vanellus miles, Australian King- Parrot Alisterus scapularis, Lewin’s Honeyeater Meliphaga lewinii, Eastern Yellow Robin Eopsaltria australis and Australian Magpie Gymnorhina tibicen) and the relationship with light energy intensity were investigated on the New South Wales Midnorth Coast, eastern Australia. It was determined that each species responded to a specific threshold light intensity as a trigger to commence singing. The timing of song commencement aligned with shifts in the required threshold light level, which was influenced by environmental variables such as moonlight (earlier) and cloudiness (later for some species). It is proposed that the structured routine of the first song of some birds, during nautical twilight, is a result of evolutionary variations in their eye structure, resulting in varying perceptions of the first morning light from the sky, leading to species commencing singing at different times.