The short-eared owl is a widespread species, found in many countries but it's survival in Europe is now a European conservation concern with amber status - find out more on the RSPB website.
Its numbers are regulated by the population levels of voles and other small rodents; there are probably about 1,000 pairs of short-eared owls in Britain when voles are scarce, but after a glut of voles, there may be 5 times this number.
The owl is a predator at the top of several food chains, and if numbers of its prey were to be drastically reduced in some way, then it would follow that the owl's numbers would also suffer. Destruction of suitable owl habitat would also affect it.