Changes in the numbers and interspecific interactions of Red Grouse (Lagopus lagopus scoticus) and Black Grouse (Tetrao tetrix)

PARR R., WATSON A. and Moss R.

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Numbers of Red Grouse Lagopus lagopus scoticus and Black Grouse Tetrao tetrix fluctuated over the years on three Scottish moors where both lived. Black Grouse tended to peak in numbers at, or one or two years after, a trough in Red Grouse numbers. During interspecific disputes in the wild and in captivity, the smaller Red Grouse usually dominated the Black Grouse. We discuss the possibility that Red Grouse at high densities depress Black Grouse numbers on moorland through aggressive competition, and speculate whether such interactions have adaptive value.