The Swiftly Evolving Blackcap

Evolution doesn’t have to take centuries. In the case of the Blackcap songbird, () ________ decades were enough. The birds breed in the forests of southern Germany, and traditionally fly to Spain for the winter. Most still make the journey south, but since the 1960s, 10% () ________ to wintering in England, where the colder climate is more than (3) ________ by the food left out on bird tables – a postwar phenomenon. These birds have rounder wings than their Spanish cousins (which provide better mobility but are () ________ suited to long-distance flight) and longer, narrower beaks, better suited to bread and nuts than to olives. Researchers speculate that if the birds () ________ to evolve in this way, they could eventually become a distinct species.