They seem harmless. What effects do they have on the environment?
Well, Mute Swans are nowhere near harmless. They are actually a threat to humans because of their aggressive behavior, they have been known to attack humans that pose a "threat". When the female is incubating her nest, the male swan will hiss at and attack anything that gets too close.
The Mute Swan poses a formidable threat to native wildlife because they have been known to overgraze, thus reducing the amount of food for other animals and messing up the whole ecosystem in that area. An adult needs about 3-4 kg of submerged aquatic plants, and whatever it doesn't eat, it either uproots and leaves or uses for its nest. This destructive behavior keeps the swan population growing, but it also can wipe out species of native plants, preventing them from ever growing back for other animals once the swans have moved on.
Also, Mute Swans can create large territories (several acres) which forces other waterfowl to leave even if there is enough food for them. The other birds often have to abandon their nests in order to get out of the way of the Mute Swan, or else they would attack and kill them.
The Mute Swan poses a formidable threat to native wildlife because they have been known to overgraze, thus reducing the amount of food for other animals and messing up the whole ecosystem in that area. An adult needs about 3-4 kg of submerged aquatic plants, and whatever it doesn't eat, it either uproots and leaves or uses for its nest. This destructive behavior keeps the swan population growing, but it also can wipe out species of native plants, preventing them from ever growing back for other animals once the swans have moved on.
Also, Mute Swans can create large territories (several acres) which forces other waterfowl to leave even if there is enough food for them. The other birds often have to abandon their nests in order to get out of the way of the Mute Swan, or else they would attack and kill them.