Willow Ptarmigan (Lagopus lagopus) Science Article 2
The location of the boundary between the territories of red grouse (Lagopus lagopus scoticus) and ptarmigan (Lagopus mutus) is related to the vegetation of the hills where both these species occur. If the he vegetation is dominated by tall, vigorous Calluna vulgaris, grouse occur. At greater altitudes where Calluna is shorter and less vigorous, significant levels of Empetrum hermaphroditum and Vaccinium myrtillus are also present and such vegetation is occupied by ptarmigan. An hypothesis is suggested in which the actual boundary between the two bird species is related to a critical height of Calluna. The different behaviour of the birds in relation to predators may influence the location of the boundary. Grouse shelter in tall all Calluna while ptarmigan seek rock heaps.
M. N. Foggo, NEW ZEALAND JOURNAL OF ECOLOGY, VOL. 3, 1980