White-tailed eagles represent no competition for fishermen. This has been shown by researchers of the German Leibniz Institute for Zoo and Wildlife Research (IZW) based on the first field study about the foraging behaviour of the white-tailed eagle (Haliaeetus albicilla) in Northern Germany. Furthermore, the study, published in the Journal of Ornithology, allows important insights in the hunting behaviour and relevant conservation measures of this species.
White-tailed eagles hunt mainly in riparian zones of lakes. Their preferred prey fishes are in size classes of 30 -- 50cm. Sea eagles are specialised particularly in catching carp bream, a fish species which is not used commercially. They modify their foraging strategy depending on weather conditions and food availability. Besides fish, waterfowls -- in particular slow moving species such as coot -- and carrion of wild animals like deer and wild boars are part of their food spectrum. Therefore white-tailed eagles represent no competition for fishermen.
White-tailed eagles generally pursue a "sit-and-wait" hunting mode. The current study shows that they spend approximately 80 % of their time with perching and only 7 % with flight activities. The "sit-and-wait" strategy is a low-cost and highly profitable foraging mode for these big and heavy raptors, by allowing highest strike success on the basis of surprise attacks. Since the animals need perches for this foraging behaviour, riparian forests and solitary trees are a key element of the hunting mode of white-tailed eagles. This new understanding contains important information for effective conservation measures of the white-tailed eagle populations. "Our results suggest that the conservation of riparian wooded corridors of around 100 m in width would be mandatory to protect the most relevant perches and thus the core zone within the hunting grounds of eagles," says Dr Oliver Krone, scientist at the IZW. Artificial perches such as poles can also be used as a simple and effective management tool given that they are not positioned too close to cycle and hiking trails.
The white-tailed eagle is one of the biggest European raptor birds. Within the last two centuries, the population recovered on the basis of intense protection measures from the border of extinction. Nevertheless, there are a number of threats which locally lead to substantial losses amongst this species. Causes are lead poisoning, collision with trains and wires, and electrocution. Lead poisoning represents an increased risk for the animals, particularly in winter. In this season, the strike success drops owed by a decrease in food availability. Thus, the animals need to extent their hunting area and forage flight durations to feed opportunistically on game carrion. But since the game carrion is often a main source of lead bullet fragments, it actually poses a severe risk to white-tailed eagles. The new study provides the scientific basis for a practical and effective conservation of white-tailed eagles.
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