Four in the morning and a barn owl hunts over the hay meadows for another hour before heading to the barns where there is surely a brood of young waiting to be fed; it is a fruitless hour of quartering and the occasional dive into the sward before reappearing empty handed. The grasses, mainly false oat-grass and Yorkshire fog, create a dense, high sward and hold its main prey, field voles.

The problem for breeding barn owls is that vole numbers are cyclical, so there is a peak every three of four years after which numbers crash and then rebuild. The success of both barn owl nests and adult survival is closely tied to the vole cycle. More interesting perhaps than the fate of barn owls, is that the causes of population cycles in voles (and lemmings, ptarmigan, grouse and snowshoe hares) are still not yet fully understood, even though they were famously, first identified by Charles Elton about 100 years ago from 250 years of snowshoe hare trapping returns logged by the Hudson Bay Company.