Because hares provide the most significant food resource for golden eagles, the peaks and troughs of hare populations can have a significant knock-on effect on eagle numbers, and especially on breeding success in a given year. In extreme years, the hare population may be reduced to as little as 10% of its maximum numbers. Though these losses are dramatic, as long as natural recovery is not hampered, populations of both hares and eagles can bounce back rapidly. However, an expanding body of evidence including data gathered by the BTO and Game and Wildlife Conservation Trust (GWCT), and an extraordinary 60-year survey of hare numbers by veteran Scottish ecologist Adam Watson, indicate that the species is undergoing a sustained decline. On some moorland estates, where traditional management involves predator control and rotational burning of heather, numbers sometimes boom, but many former stronghold areas have been planted with trees and no longer support any hares at all, and in many areas where hares do still live, their numbers appear to be down.
In extreme years, the hare population may be reduced to as little as 10% of its maximum numbers.