Trumpeter Swans form pair bonds when they are three or four years old. The pair stays together throughout the year, moving together in migratory populations. Trumpeters are assumed to mate for life, but some individuals do switch mates over their lifetimes. Some males that lost their mates did not mate again. Trumpeter Swans are impressively large — males average over 26 pounds, making them North America’s heaviest flying bird. To get that much mass aloft the swans need at least a 100 meter-long “runway” of open water: running hard across the surface, they almost sound like galloping horses as they generate speed for take-off.