The most widespread-breeding sandpiper in North America, the Spotted Sandpiper is found east-west across the continent and north-south from the southern edge of the Arctic to the southern states. This species has colonized this broad range by capitalizing on generalist habits; i.e., individuals feed on a great variety of animal matter and occupy almost all habitats near water, everything from the shorelines of wild rivers and lakes to urban and agricultural ponds and pools. Easily identified in breeding plumage by the presence of dense ventral spots, the Spotted Sandpiper is also known as a little shorebird teetering along the water's edge. This characteristic teetering behavior has led to the common names of teeter-peep, teeter-bob, jerk or perk bird, teeter-snipe, and tip-tail ( Nelson 1939 ). The unique flight of this species-low over the water with shallow, stiff wing beats-is also characteristic. While many shorebirds are known for their spectacular migratory gatherings, Spotted Sandpipers migrate singly or in small groups to their wintering grounds, which extend from the extreme southern United States to southern South America.
In preparing this account, we have taken broad advantage of a fine unpublished doctoral dissertation by Theodora Nelson. This excellent early study (1926-1936) was extremely valuable for preparation of the sections on migration, feeding, breeding, molts and plumages, and development. Our account also relies heavily on studies in Minnesota, first at Lake Itasca (1969-1972) and then at Leech Lake (1973-1991), where more than a thousand individually marked Spotted Sandpipers were studied by LWO and associates (e.g., Maxson and Oring 1980 , Oring et al. 1983 , Lank et al. 1985 , Oring et al. 1991a , Oring et al. 1992 ). Publications resulting from this work and referred to in the text -- which include the topics of behavior, ecology, population biology, reproductive endocrinology, and genetics -- were based on different subsets of the total study. These works revealed the details of an amazing and previously little-understood breeding system that now is one of the best known among birds.
Spotted Sandpipers (along with several other species of scolopacids) are among a small minority of birds that have reversed sex roles; i.e., females are more aggressive and active in courtship than males, and males take the primary parental role. In contrast to the normal pattern in birds, female Spotted Sandpipers arrive first on the breeding grounds, stake out territories, and attempt to attract males. This was the first migratory bird species in which females were found to arrive on the breeding grounds before males. And other Spotted Sandpiper patterns are also unusual to shorebirds: Females are larger than males, female chicks are at least as likely to return to the place where they hatched for their first breeding attempt as males, and breeding females are at least as site-tenacious as males.
Spotted Sandpipers also were the first bird species in which males were found to have higher levels than females of prolactin, a pituitary hormone known for its promotion of parental care. This finding is associated with the greater male parental care typical of this species. Perhaps most interesting is the fact that Spotted Sandpipers exhibit classic polyandry-a mating system in which females mate with up to 4 males, each of which cares for a clutch and a brood. One female on Little Pelican Island, Leech Lake, Minnesota, laid 5 clutches for 3 males in 43 days. At other times and places, however, Spotted Sandpipers breed monogamously, and females help care for young. Such great variation in breeding tactics makes this a fascinating species for the study of how variations in environmental conditions alter the expression and evolution of behavioral and physiological traits.