Male red grouse mark out their territories with an energetic display during which they leap into the air, giving their characteristic 'go-back-go-back' call. They compete for an area of moor with plenty of heather and bilberry bushes in which the female will produce a nest scrape for her eggs. These eggs are well camouflaged, laid in April and may number ten or more. The chicks hatch after about three weeks, and are fed by both birds for six weeks. They can fly after 13 days. Red grouse have been a quarry species for years, but the sport only became a source of lucrative business when the breech-loading gun was invented in the mid 19th century, and the railways provided access to the moors. The 'Glorious twelfth' of August, the opening of the grouse-shooting season, was apparently chosen to fit in with the parliamentary summer recess, as well as the birds' breeding season.