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THE GOLDEN EAGLE IN RELATION TO ITS FOOD SUPPLY
Author(s) -
Brown Leslie H.,
Watson Adam
Publication year - 1964
Publication title -
ibis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.933
H-Index - 80
eISSN - 1474-919X
pISSN - 0019-1019
DOI - 10.1111/j.1474-919x.1964.tb03682.x
Subject(s) - eagle , carrion , predation , range (aeronautics) , nest (protein structural motif) , food supply , geography , habitat , population density , population , ecology , biology , fishery , demography , biochemistry , materials science , sociology , composite material , agricultural science
Summary The population of Golden Eagles was assessed in four different areas of the Scottish Highlands. The average area per pair varied from 11,400 to 17,884 acres, excluding country that was not used by the eagles. Eagle food in these areas consists largely of Red Grouse, Ptarmigan, Mountain Hares and Rabbits, and also dead Red Deer and dead sheep. The numbers and biomass of the four main species of living prey were assessed by representative counts in three main types of habitat; and of dead deer and sheep partly from counts but mainly from published data on stocking densities, mortality and weights. The annual food requirement from a home range was estimated at 249 kg. of meat, calculated from data on the food consumption of eagles, allowing for known breeding success and for the presence of some immature eagles and unmated adults; and this was compared with the total food potential in the four Study Areas, allowance being made for the inedible portions of carcases. The average food potential in all areas is greatly in excess of the requirements. In the three western areas living prey is very scarce, but amounts of carrion are large and the eagles in these areas depend mainly on carrion. Large differences in food potential between areas do not correspond with differences in eagle density. Two examples are cited where a drastic reduction in food supply had no effect on eagle density, which remains remarkably constant in spite of seasonal and annual fluctuations in food supply. Golden Eagle nest‐sites are used over many years, and the home ranges are big enough to supply a more than adequate food supply at all times of year. Evidence is provided of territorial or home‐range defence, which generally takes the form of display flights but occasionally involves more overt aggression. The home‐range size is fixed so high that a critical food level is probably very rarely reached.