KINGSTON, R.I. – April 3, 2014 – A postdoctoral researcher at the University of Rhode Island tracked the fall migration of songbirds through Rhode Island by listening to their nocturnal flight calls using eight microphones set up around the state. His results confirm what studies using radar have found — that weather conditions significantly influence migratory behavior – but because he could detect individual species, he believes this method will help researchers identify changes in the timing of migration as the climate changes.
His results were published in the online research journal PLOS ONE in March.
Adam Smith said that using acoustics is a simpler and more affordable method than radar to monitor songbird migration. His microphones detected more than 42,000 individual flight calls from at least 22 species of warblers and sparrows in September and October of 2010 and 2011 at five sites on Block Island and three coastal wildlife refuges.
“The aim was to characterize the atmospheric conditions that lead to higher coastal migratory activity,” Smith said. “What we know about this activity is based largely on radar studies, and I wanted to know if we could get the same kind of information from acoustic data.”
He did. Smith detected more flight calls in the nights following the passage of cold fronts, which is when he says many songbirds prefer to migrate. “Wind speeds and wind direction are important,” he said. “And precipitation inhibits migration.”
He also found that birds called more during cloudy conditions. He believes that the poor visibility may prompt a behavioral response in the birds to maintain contact and coordinate migratory behavior. Cloudy conditions may also cause the birds to fly at a lower altitude, which might increase the likelihood that their calls were detected.
The somewhat counterintuitive result was that Smith found more birds migrating along the coast rather than offshore.
“People tend to associate offshore islands like Block Island and Nantucket with being important migratory stopover locations because birds are apparently abundant and easily observed there,” he said. “But most songbirds don’t really like to migrate over the water. It’s largely a mistake when songbirds appear offshore, and once they find themselves there, most start working their way back to the mainland. The vast majority of migration is along the coast and inland.”
According to Smith, most coastal fall migrants are immature birds making their first long-distance migration, and their “naïve navigational systems” are often insufficient to help them avoid traveling along the Atlantic coast. That’s why most songbird migrants found on offshore islands are immature birds.
Smith, an Indiana native who earned his doctorate from URI, began his study seeking to learn whether migratory songbirds will be affected by offshore wind turbines. “We don’t know enough about what happens to the birds that are displaced offshore, but it’s clear that most of songbird migration occurs along the coast or inland, so the majority of songbird species aren’t likely to be affected much by offshore wind farms.”
His next study will examine seabird distribution and abundance in the context of offshore wind development.
Perhaps the most useful result of his study, however, is the confirmation that acoustic data can be an important means for monitoring migration.
“Not all bird species use flight calls, so only a subset of migratory songbird activity can be monitored this way, but it’s an excellent complement to other tools,” he said. “It’s relatively simple, inexpensive, continuous and has less logistical issues than most alternatives. So it’s a useful tool in the pocket of ornithologists.”
Pictured above: URI postdoctoral researcher Adam Smith sets up a recorder to detect nocturnal birdcalls on Block Island. (Photo courtesy of Adam Smith)