Ecology: Cuckoos pay the cost of migratory short-cut

Population decline in the Common Cuckoo is linked to choice of migratory route, suggests a study in Nature Communications. The paper finds that migratory cuckoos that choose a shorter route in their migratory journey across the Sahara desert have higher mortality rates than those flying across longer distances.

The Common Cuckoo, a brood parasite that relies on other bird species to raise its young, is declining in certain breeding populations across the UK. It has been unclear why some populations are declining at greater rates than others.

Chris Hewson and colleagues use satellite tags to track 42 male Common Cuckoos from the rapidly declining UK population during 56 autumn migrations in 2011-2014. They monitored their mortality during migration. The authors find that birds from declining breeding populations are more likely to migrate to winter breeding grounds in central Africa along a Western route (via Spain) than along an Eastern route (via Italy and the Balkans). They record a higher mortality along the shorter, western route and showed that this higher mortality occurred prior to reaching the Sahara desert. The authors suggest that birds may have encountered challenging drought conditions in Spain.

These findings demonstrate that routes taken during migrations can thus influence population success at breeding sites. Considering how conditions at stopover sites contribute to mortality during migration is critical to predicting future success of the cuckoo and other migratory birds, the authors suggest.