The number of nightjars recorded in a national park is thought to have doubled in the past five years following conservation efforts. Seventy eight of the elusive birds, which are known for their "churring" song at sunset, were recorded last year in an ecological survey within the South Downs National Park. A spokesman for the South Downs National Park Authority (SDNPA) described it as "a remarkable comeback" and was "thanks to nature recovery efforts and better habitat management". The survey also found 109 nightjar territories, the highest recorded, in the lowland heaths of east Hampshire, including Woolmer Forest and the commons of Shortheath, Bramshott, Ludshott, Broxhead and Kingsley. Nightjars are crepuscular ground-nesting birds - meaning they emerge at twilight and can be seen hunting for food at dusk and dawn. The birds migrate 4,000 miles (6,437 km) from the Democratic Republic of Congo each spring and remain from April to August.…