This paper analyses the weight loss in Oystercatchers on the roost and
after capture and attempts to investigate to what degree this weight
loss is due to defecation of digested food, to dehydration and to util
isation of nutrient stores. The study emphasizes the need to record we
ight changes relative to the time of arrival at the roost, rather than
relative to time since capture, as is common practice in correcting f
or weight loss In captive birds. If food is still defecated, the weigh
t loss is 4.3 times as large as when the gut is empty. From then on, p
robably 10% of the weight loss is due to dehydration. It is estimated
that the rest of the remaining weight decrease is about equally due to
loss of dry lean muscles and fat. The weight loss of waders of differ
ent size is a function of body weight(3/4).