which travel in an erratic, wavelike flight pattern. Its winter range includes southern Canada and stretches south through the United States to parts of Mexico. In winter, in the northern part of its range, the finch may move nearer to feeders if they are available. In southern ranges, during winter, they remain in areas like fields and flood plains where they live during the summer months. Attempts were made to introduce the American goldfinch into Bermuda in the 19th century and Tahiti in 1938, but the species failed to become established in either place. Behavior The American goldfinch flies in a distinctive undulating pattern, creating a wave-shaped path. This normally consists of a series of wing beats to lift the bird, then folding in the wings and gliding in an arc before repeating the pattern. Birds often vocalize during the flapping phase of the pattern and then go silent during the coasting phase. The call made during flight is "per-twee-twee-twee", or "ti-di-di-di", punctuated by the silent periods. They communicate with several distinct vocalizations, including one that sounds like "po-ta-to-chip" to the listener. Birds do not act aggressively toward predators within their territory; their only reaction is alarm calling. Predators include snakes, weasels, squirrels, and blue jays, which may destroy eggs or kill young, and hawks and cats, which pose a threat to both young and adults. The oldest known American goldfinch was 10 years and 5 months old. Sociality The American goldfinch is gregarious during the non-breeding season when it is often found in large flocks, usually with other finches. The social hierarchy, measured by how many aggressive encounters are won by each individual, tends towards the male being dominant in the non-breeding season. During the breeding season, this finch lives in loose colonies. While the nest is being constructed, the male will act aggressively toward other males who intrude into his territory, driving them away, and the female reacts in the same way toward other females. This aggressiveness subsides once the eggs have been laid. The social hierarchy in the breeding season generally has the female dominant over the male. Dominance may change based on the value of a resource; a study published in 1987 found that starved subordinate birds were sometimes dominant in competitions over feeder access. Birds indicate their level of aggression through a range of displays. The head-up display, where the neck and legs are slightly