This is bird note. Some birds have always called nocturnally, such as night jars, mockingbirds, and owls.

But other species are relative newcomers to the nighttime music scene, especially in urban areas.

In cities in the US, some American Robbins put on a show long before sunrise.

Researchers are studying why certain songbirds sing nocturnally in cities.

Some studies suggest that artificial lighting from street lamps and buildings

could lead birds to treat the night like the day.

However, some experiments with artificial lights

showed no effect on singing behavior. For some birds it seems that noise is an

important factor.

A study in the United Kingdom

found that European Robbins in noisier environments

tend to sing at night.

The finding suggests that these Robins experience nighttime as the best

time to have their voice heard by potential mates and rivals after the days hustle and bustle.

Whatever the cause, birds singing at night are one more thing,

like rumbling trains and passing cars

that city dwellers learn to sleep through.

For Bird Note, I'm Michael Stein.