One of the natural enemies of the Greater Spotted Eagle is the marten Martes martes. Almost every year, this predator destroys part of the breeding of this rarest of eagles by eating their eggs or chicks. In some years martens are responsible for the loss of almost 50% of the breeds and their victims are even the almost flightless young. The martens know the voice of the young eagles. In June, July or early August, a young eagle calling from its nest for food (the voice of the Greater Spotted Eagle is very loud) attracts the mammal and becomes an easy prey. The martens also learn the location of the nests in the area they are penetrating and visit them regularly. If such 'visits’ occur in spring, they can result in the destruction of the eagle’s eggs, which are unable to defend them. This predator uses the eagles’ nests for resting and often also for rearing its own young. It then digs up the nest to create a nesting chamber inside, where it gives birth to its own young. Such a marten-occupied nest is quickly destroyed. Given that sometimes one in several thousand trees in the forest is suitable for nesting by eagles, this mammal can make it almost impossible for them to nest successfully in the area.
Photo 1. Photo-recorded marten on a nest.
To counteract this, the LIFE team has developed an artificial nest platform with an aluminium truss-reinforced structure that prevents martens from ditching it and rearing their young. All natural nests as well as the artificial platforms are additionally protected by trunk-mounted specially constructed protective collars, which are very difficult to overcome. In winter 2023/2024, 20 such collars were installed. A spring check showed that martens were making unsuccessful attempts to force their way through this protection. Not a single nest where we applied such protection saw martens emerge. In the spring, we also applied a repellent repellent to further discourage this mammal. We hope that thanks to this, more young eagles will fly out of the Biebrza forests this year.
