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Population Fluctuations in the Red Grouse Lagopus lagopus scoticus

David Jenkins, Adam Watson and G. R. Miller
Journal of Animal Ecology
Vol. 36, No. 1 (Feb., 1967), pp. 97-122
DOI: 10.2307/3017
Stable URL: http://www.jstor.org/stable/3017
Page Count: 26
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Population Fluctuations in the Red Grouse Lagopus lagopus scoticus
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Abstract

1. Population studies on red grouse at Kerloch gave results similar to Glen Esk (Jenkins et al. 1963), except that breeding stocks at Kerloch did not change greatly from year to year. 2. Breeding birds took territories in autumn, and expelled non-territorial surplus birds in one to three sudden stages, depending partly on the number of surplus birds. Decreases usually occurred in autumn but were recorded in every month from August to April. Numbers were stable between decreases. 3. Most surplus birds died, but mortality was a consequence of social behaviour and was not primarily important in population control. 4. Nearly all cocks died within 1.5 km of where they were reared, and hence immigration and emigration were not important in controlling the breeding stock. 5. Tests suggest that we found about two-thirds of the grouse killed by predators and about one-half of the grouse dying naturally from non-violent causes. Since most birds that died were surplus, predation of adults on the moor did not reduce breeding stocks. 6. The sex ratio in the spring population was correlated with the sex ratio of young birds shot in the previous August. Assuming that the ratio was 1:1 in the laid eggs, more female than male embryos or chicks died in some years. 7. Annual differences in clutch size cannot be attributed solely to differences in laying date. 8. Laying date, clutch size and chick survival were related to the amount of green heather in April. Chick mortality cannot be explained by bad weather in June. 9. Stocks were much higher on moors on base-rich rocks than on moors on base-deficient rocks, despite apparently similar survival of birds reared on both. 10. Changes in breeding density from one spring to the next were correlated with breeding success in the intervening summer on base-deficient and intermediate moors, but not on the base-rich moors where good breeding did not produce an increase in breeding stocks. 11. Differences in the average breeding stocks over a number of years between moors on poor and rich rocks were associated with variable breeding success on the poor ground and consistently better breeding on the richer moors.

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