SCORING ABDOMINAL PROFILES TO CHARACTERIZE MIGRATORY COHORTS OF SHOREBIRDS - AN EXAMPLE WITH RED KNOTS

This paper explores whether the visual scoring of abdominal profiles c an be used to evaluate variation in energy stores of shorebirds. Carca ss analyses showed that the mass of fat in the abdominal cavity is wel l correlated with total fat mass and body mass. In May 1990, abdominal profiles were scored of Red Knots (Calidris canutus, subspecies canut us) on their last spring staging area in northern Germany before the 4 000-5000-km long flight to the Siberian-arctic breeding grounds. Score s made in the field varied between 1 (concave shape of abdomen) to 5 ( bulging). Average abdominal profile scores increased significantly ove r time in May 1990, paralleled by an increase in body mass, as based o n catches of Red Knots in earlier years. At the end of May the average abdominal profile decreased, presumably due to the departure of adult Red Knots, leaving lean, perhaps mainly immature, birds behind. The s cale of abdominal profile scores is probably too coarse to estimate fa t content of individual waders. On a cohort level, however, the measur e has much potential for comparisons of (re-)fuelling rates between di fferent groups, feeding areas and years without the need to obtain lar ge samples of captured birds.