The utilisation of heather moorland by red grouse
The utilisation of heather moorland by red grouse Lagopus lagopus scoticus was studied with particular emphasis on the influences of vegetation structure on grouse behaviour at a series of spatial scales, from the choice of location within individual heather stands up to the composition and alignment of territories on the moor. A novel method of measurement and multivariate statistical analysis was developed for quantifying the structure of vegetation dominated by ling heather Calluna vulgaris. The method was assessed in relation to existing subjective classifications. The method revealed that gaps in the canopy of tall heather were utilised by grouse during the daytime in winter. The manner in which grouse exploit the vegetation types available in their territories was determined by radio-tracking a population on a managed grouse moor in north-east Scotland over the course of two years. During autumn and winter, territorial grouse showed a preference for tall heather relative to its availability. In spring, a greater use was made of heterogeneous mixtures of heather and graminoids during the daytime, and, to some extent, of shorter heather during the intensive feeding periods at dawn and dusk. Hens showed a very strong affinity for edge between heather stands in spring, but spent more time on the side offering the greater cover. Broods tended to range in areas with more old heather and more edge than generally available, but within their ranges, they clearly preferred heterogeneous areas. The relationships between vegetation patterns, the composition of territories and the alignment of territory boundaries were investigated using fifteen years' historical data. The relationships varied considerably between years. When the population was declining, heather edge was distributed evenly between territories, but it was distributed unevenly during population increase. In general, territory alignment showed a greater association with vegetation edges than with particular types of vegetation.