Do streetlights make the mostly daytime-active willie wagtail more or less likely to sing at night?

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Artificial light at night (ALAN) has rapidly and drastically changed the global nocturnal environment. Evidence that ALAN affects animal behaviour is growing. Animals encounter both point sources, such as streetlights and other nearby lights, and broadscale illumination in the form of skyglow.

Research has typically assessed ALAN in a simplified way, but fully understanding its ecological impact requires considering different scales and sources of light together. The relationship between bird song and light has already been well studied, making bird song an opportunity to examine the relative behavioural effects of different light sources.

This study combined correlational observations and experimental approaches to examine how light at night affects nocturnal song in the largely diurnal willie wagtail (Rhipidura leucophrys).

Observations across urban and rural locations in southeastern Australia showed that nocturnal song behaviour increased with moonlight intensity in darker rural areas but decreased in areas with high skyglow. In both urban and rural areas, willie wagtails were half as likely to sing at night in the presence of localized light sources such as streetlights.

The researchers also experimentally introduced streetlights into a previously dark area. Song rates declined when the lights were turned on and returned to their original rates after the streetlights were removed, confirming the relationship.

The findings show that the spatial scale of light, as well as its intensity, matters when considering the effects of light at night: moonlight, skyglow and localized artificial light sources have different effects on nocturnal song behaviour.