Fluctuations in the Numbers of British Tetraonids

By the courtesy of the owners and factors, I have been able to get grouse bags for varying periods from many game books. These are treasured personal possessions and my very sincere thanks are due to my correspondents, without whose co-operation little could have been done. The British red grouse (Lagopus scoticus (Lath)) called 'grouse' in this paper, is reputed to have a cycle of 7 years, and game-book records of bags distributed over the whole range have been collected to see to what extent such fluctuations occur and their time and space relations inter se. At the same time data were collected for the other three British tetraonids, the capercailzie (Tetrao urogallus L.), the black grouse or blackgame (Lyrurus tetrix L.) and the ptarmigan (Lagopus mutus (Montin)). It proved more difficult to get satisfactory figures for these species than for grouse, and the numbers everywhere were much smaller. The main figures came from central Scotland, Perth and Angus, with blackgame from eight big shoots in south Scotland for comparison. The game-book data cover a long period, some back to the 1830's and many to the fifties. The figures are those of birds shot and not of populations. A low number or zero does not mean that the population is nil as low stocks are conserved, but on a 10,000-acre moor the stock was said to be four birds the year after the bag had been 3402 (Committee of Inquiry on Grouse Disease 1912, p. 443). When stocks are very big it is unlikely that the whole shootable surplus is killed as the birds get wild and