Production, dieback and grazing of heather (Calluna vulgaris) in relation to numbers of red grouse (Lagopus l. scoticus) and mountain hares (Lepus timidus) in north-east Scotland.
The summer growth, winter dieback and grazing of shoots and flowers of heather was measured at 2 moors in N.E. Scotland. The main factor determining annual variations in the amount of shoots and flowers left in spring was grazing at one moor and dieback at the other. Using counts published by other workers, correlations amongst the amount of heather left in spring, the density of grouse and the density of hares were found at one moor, and were interpreted as evidence of competition for food between grouse and hares. At the other moor, hare numbers declined following heavy grazing by hares themselves. The suggestion of competition for food seemed paradoxical in view of the large amounts of heather remaining uneaten in spring. To explain this it is pointed out that grouse and hares are selective feeders, and it is suggested that the less heather there is present the harder the animals find it to select a diet providing an adequate plane of nutrition.