<P> Mute swans nest on large mounds that they build with waterside vegetation in shallow water on islands in the middle or at the very edge of a lake . They are monogamous and often reuse the same nest each year, restoring or rebuilding it as needed . Male and female swans share the care of the nest, and once the cygnets are fledged it is not uncommon to see whole families looking for food. They feed on a wide range of vegetation, both submerged aquatic plants which they reach with their long necks, and by grazing on land . The food commonly includes agricultural crop plants such as oilseed rape and wheat, and feeding flocks in the winter may cause significant crop damage, often as much through trampling with their large webbed feet, as through direct consumption . </P> <P> Unlike black swans, mute swans are usually strongly territorial with just a single pair on smaller lakes, though in a few locations where a large area of suitable feeding habitat is found they can be colonial . The largest colonies have over 100 pairs, such as at the colony at Abbotsbury Swannery in southern England, and at the southern tip of Öland Island, Ottenby Preserve, in the coastal waters of the Baltic Sea, and can have nests spaced as little as 2 m (7 ft) apart . Non-mated juveniles up to 3--4 years old commonly form larger flocks, which can total several hundred birds, often at regular traditional sites . A notable flock of non-breeding birds is found on the River Tweed estuary at Berwick - upon - Tweed in northeastern England, with a maximum count of 787 birds . A large population exists near the Swan Lifeline Station in Windsor, and live on the Thames in the shadow of Windsor Castle . Once the adults are mated they seek out their own territories and often live close to ducks and gulls, which may take advantage of the swan's ability to reach deep water weeds, which tend to spread out on the water surface . </P> <P> The mute swan is less vocal than the noisy whooper and Bewick's swans; they do, however, make a variety of grunting, hoarse whistling, and snorting noises, especially in communicating with their cygnets, and usually hiss at competitors or intruders trying to enter their territory . The most familiar sound associated with mute swan is the vibrant throbbing of the wings in flight which is unique to the species, and can be heard from a range of 1 to 2 km (0.6 to 1 mi), indicating its value as a contact sound between birds in flight . Cygnets are especially vocal, and communicate through a variety of whistling and chirping sounds when content, as well as a harsh squawking noise when distressed or lost . </P> <P> Mute swans can be very aggressive in defence of their nests and are highly protective of their mate and offspring . Most defensive attacks from a mute swan begin with a loud hiss and, if this is not sufficient to drive off the predator, are followed by a physical attack . Swans attack by smashing at their enemy with bony spurs in the wings, accompanied by biting with their large bill . The wings of the swan are very powerful, though not strong enough to break an adult man's leg, as said anecdotally . Large waterfowl, such as Canada geese, (more likely out of competition than in response to potential predation) may be aggressively driven off, and mute swans regularly attack people who enter their territory . The cob is responsible for defending the cygnets while on the water, and will sometimes attack small watercraft, such as canoes, that it feels are a threat to its young . The cob will additionally try and chase the predator out of his family territory, and will keep animals such as foxes and raptors at bay . In New York (outside its native range), the most common predators of cygnets are common snapping turtles . Healthy adults are rarely preyed upon, though canids such as coyotes, felids such as lynxes, and bears can pose a threat to infirm ones (healthy adults can usually swim away from danger unless defending nests) and there are a few cases of healthy adults falling prey to golden eagles . In England, there has been an increased rate of attacks on swans by out - of - control dogs, especially in parks where the birds are less territorial . This is considered criminal in British law, and the birds are placed under the highest protection due to their association with the Monarch . </P>

Why is the mute swan the national animal of denmark