Abstract: Through the description and analysis of the body-and organ phenotypes of  Calidris tenuirostris  at its stopover in Shanghai during spring migration, this paper studied the changes in the phenotypic flexibility of the body structure of the bird. During springtime stopover, the body mass of  C. tenuirostris increased significantly, with the maximum increment being about 52.2% of the mean body mass. This increase was mainly of fat mass increase, followed by pectoral muscle mass increase. There was a linear correlation between pectoral muscle mass and body mass. Leg muscle mass and heart mass also had an increasing trend with the increase of body mass. The changes in digestive organs manifested in two aspects,  i.e ., the mass increase of digestive glands (liver and pancreas) and the less change in digestive tracts (gizzard and intestine), which would promote the foraging efficiency rapidly and save the energy and time for restoration to maximize the migration speed, and benefit to the reservation of definite spare space for digestion. The other organs including brain, lung, kidney, spleen, eyes, and salt glands were in homeostatic during stopover.

Key words: Soil fauna, Forest, Changbai Mountain, Secondary succession