Geoff provided the following additional explanation: The 1993 figures are taken from the English Nature bird survey. The 2004 data comes from the Sheffield Bird Study Group survey carried out for the National Trust. It was reported that Skylarks and Pipits were too numerous to count.
In 2010, an increase in grouse, and hares has been observed, the number of skylarks has dropped slightly, but other species have been maintained at the same level. Populations of Snipe, Black grouse, Merlin, Kestrel, Raven, and Peregrines are thought to have increased and in 2006, Hen Harriers hunted the moor.