For these birds, climate change spells a rise in fatal conflicts

January 10, 2019, Cell Press

Researchers have found yet another way in which climate change has been detrimental to migrating birds. As European winters have become warmer, pied flycatchers traveling from Africa over long distances to reach breeding grounds in the Netherlands are arriving to find that resident great tits have already claimed nesting sites for the season. As a result, the number of flycatchers killed in great tit nests has risen dramatically. The work appears January 10 in the journal Current Biology.

"When pied flycatchers and great tits are more synchronous in their timing, this leads to a higher level of conflict over nesting sites," says Jelmer Samplonius, who did the work at the University of Groningen, the Netherlands, and is now at the University of Edinburgh, UK.

Samplonius's team got interested in the dynamics between pied flycatchers and great tits in part because both species rely on a short burst of food resources—caterpillars—to raise their young. When the birds' timing is well matched with the caterpillar peak, they are more successful in raising their offspring.

Given the reliance on the same food and nesting resources, it was clear the two species interacted quite a bit. Pied flycatchers were known for trying to take over great tit nests. They also eavesdropped on resident great tits to gain information the long-distance migrants otherwise lack about local conditions.

After years of careful monitoring, Samplonius says, "it was hard not to notice" that many flycatchers were dying in great tit nests. In other years, "virtually none" met that same fate. Could synchrony between the two competitor species explain the variation?

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