City lights slow nighttime bird migration, study shows

University of Windsor study records bird migration paths with microphones

By Sean Previl, CBC News Posted: May 16, 2016 2:18 PM ET Last Updated: May 17, 2016 9:11 AM ET

Birds migrating at night are taking much longer flight paths because of light coming from urban centres, say researchers at the University of Windsor.

Three times more birds are taking their nighttime migratory paths through lighted towns and cities instead of taking more direct routes, the study, conducted by biology professor Dan Mennill and undergraduate student Matt Watson in fall 2013, found.

The research was published as the article, Anthropogenic light is associated with increased vocal activity by nocturnally migrating birds, in the April 2016 edition of the Condor, the journal of the Cooper Ornithological Society. 

Past research has studied how light from skyscrapers and communication towers affect these same migrations, but this is the first study to look at how low-level and ground lighting affects migratory patterns.

Birds use stars to navigate during their migration and artificial light confuses them, Mennill said. "Even a single lightbulb is enough to change the behaviour of birds migrating overhead," Mennill told CBC News.

Microphones record migration

The study started after Watson noticed more bird calls were being heard at a recording site located near a street light. The university has been studying bird migration, primarily in songbirds, through the Great Lakes, using audio recordings by pointing microphones at the sky.

A change in flight paths is a problem because the migrating birds are often travelling a long distance and flying over lit areas only increases that distance, Mennill said.

The shortest distance between two points is always a straight line, but birds that follow ground-level lighting may end up flying a zigzag pattern. Some examples, include birds bred at Ojibway Prairie Conservation Reserve in Windsor, Ont. that took a less direct route to Costa Rica.

"They need to be maximally efficient when they're moving in order to arrive at their wintering grounds in the best condition they can and then back to their breeding grounds at this time of year in the best condition they can," he said.

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