nlike 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.[20][22] Non-mated juveniles up to 3–4 years old also commonly form larger flocks, which can total several hundred birds, often at regular traditional sites.[23] 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.[24] A large population also 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