In 2011, the Horn of Africa experienced a drought so extreme that it waylaid many bird species migrating through the region on their way to breeding grounds in Europe. The drought is thought to have caused a food shortage that slowed the birds as they tried to gather enough fuel to power the rest of their long flight northward.
Anders Tøttrup of the University of Copenhagen and his colleagues followed the migration of two species in particular—the red-backed shrike and the thrush nightingale. Their tracking data revealed that in 2011 both species lingered at the Horn of Africa several days longer than they did during spring migrations in 2010 and 2012, both of which were non-drought years. In fact, in 2011, the birds' arrival to their northern European breeding grounds was among the latest documented since 1950.
Food shortages at stopover sites and the resultant migration delays could prove costly to migratory species if they reduce breeding success or increase mortality rates. Fortunately, Anders Tøttrup and his colleagues reported that for the species they studied in 2011, their population size and reproductive success was about average.
Photo © Per Ekberg / AAAS.