Change in the sex ratio of the Finnish capercaillie Tetrao urogallus population
1999
Helle, Pekka | Kurki, Sami | Lindén, Harto
Earlier reports from Fennoscandia and Russia have shown that among adult capercaillies the proportion of females is 60–65%, mainly as a consequence of high mortality of male chicks during their first months of life. The Finnish August censuses of grouse (1964–1988) show that the percentage of female capercaillie has remained unchanged at about 60–65% in northern and eastern Finland. Over the same period the percentage of females in southern and central Finland has decreased significantly from 62 to 50%. The present geographical variation in the percentage of females seems to coincide with the amount of forest in the landscape; the proportion of females is lowest in the southern and western part of Finland where the proportion of agricultural land is highest. Data from 1989–1996 show that variation in August male density among game management districts in Finland (CV%: 21.9) is significantly smaller than that of females (CV%: 33.4). This suggests that the variation in female proportion is more dependent on variation in female than in male density. The most probable reasons for the change in sex ratio include predation on females by mammalian and avian predators and selective hunting (or closing of hunting seasons), but tests of these hypotheses are premature at present.
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