Writing in the journal Science, University of Copenhagen researcher Anders Tøttrup said he and colleagues used miniature tracking devices to monitor the migratory patterns of red-backed shrikes and thrush nightingales from 2009 to 2012.
They found that the birds’ arrival in 2011 was among the latest ever before documented.
Tøttrup explains that the birds travel thousands of miles to and from their seasonal homes.
He says acute La Niña-induced drought in the northern spring of 2011 ravaged the food supplies that the birds typically fuel up on.
This made it harder for them to build up fat for the final leg of their journey, resulting in the delayed arrival.
Photos: Per Ekberg