How privileged we are to be able to observe Switzerland’s two largest breeding birds, the golden eagle and the bearded vulture, here in Saanenland. When one of these imposing birds is circling in the azure sky above the highest mountain peaks, not only the ornithologist’s heart begins to beat faster, but also that of mountaineers and hikers.
Among the approximately 320 breeding pairs of golden eagles (Aquila chrysaetos) in Switzerland, there are also some in the Saanenland. For reasons of nature conservation and to avoid disturbances, the exact location of these breeding pairs is not made public, as otherwise – as has often happened – the breeding would be aborted. Preferred locations where eagles can be observed are always regions where marmot colonies are present.
A golden eagle breeding pair, which stays together for years, usually has several nests in its territory of up to 90 square kilometres. Sometimes the same eyrie is used for two to three years, but very often they alternate from year to year and occupy a different one.
The nests, which can be up to 1.5 metres high and weigh over 100 kilograms, are almost always located in overhanging, inaccessible rock faces, usually below the tree line, so that the approach with prey (mostly marmots) is not made more difficult by a strenuous upward flight. Tree nests are relatively rare and can only be found in lower regions. Whether a nest is occupied or not can be determined by the approaching and departing adult birds. If the edge of the eyrie is covered with green branches (mostly larch), this also indicates breeding. Golden eagles start building their nests very early in the year and their usually two, rarely three eggs, which are then incubated for about 43 to 44 days, can be found in the nest as early as mid-March. If both eggs are fertilised, there will soon be a visible difference in size between the young birds, which often leads to fights between the siblings when it comes to food. Nature can be cruel, as in the case of siblicide. This means that the first-born nestling kills the younger one or even throws it out of the nest.
A good 80 days pass before the young bird flies out. During this time, it is provided with plenty of food, which the adults bring in daily. After its maiden flight, which sometimes ends fatally, the still dark-coloured young bird is taught by the adults how to hunt and catch prey. Shortly before the next breeding season, the young bird, if it has not already moved away itself, is driven out of the territory by the adult birds, as it is now already classified as a food competitor.
Depending on the territory, marmots are the golden eagles’ main prey. But squirrels, martens, hares, young foxes, fawns and chamois as well as birds from thrushes to capercaillies are also victims of the lightning-fast surprise attacks and the razor-sharp claws.
During the winter season, the eagles also make do with dead animals such as chamois and ibex who die in avalanches. If prolonged bad weather with snow and fog interferes with foraging, they can survive for up to a week by feeding on the meat reserves stored in their crop.
Size, weight and age
As with most birds of prey, female eagles are larger and heavier than the males. An adult bird can reach a wingspan of up to 2.25 m and a weight of up to 6 kg. This roughly corresponds to the maximum load the bird is capable of carrying with its fangs.
It takes some experience to establish an eagle’s age. Roughly speaking, young birds can be recognised in flight by their whitish feathers in the middle of the wing and the white band at the base of the tail, which they wear until they reach sexual maturity at around four to five years. Old birds (from five to six years onwards) are mostly dark brown in colour and have golden-yellowish head feathers – hence its name.
Since the golden eagle was placed under protection in Switzerland in 1953, it is theoretically no longer in danger of being shot. However, cable car wires and hay ropes, which can be its downfall when flying in dense fog, pose a risk of accident.
BASED ON AVS/BERT INÄBNIT
Information on the bearded vulture in the Saanenland will follow in a later issue.