BODY-COMPOSITION DYNAMICS OF RUDDY DUCKS DURING WING MOLT

A method was developed for indexing moulting costs in waterfowl based on intensity of moult and proportional mass of feathers in seven feath er regions (ADJMOLT). This method was then applied to an examination o f relations between moulting costs and size-adjusted body mass and com position of postbreeding male and female ruddy ducks (Oxyura jamaicens is) collected in southwestern Manitoba, 30 July - 24 August 1985. Mode rate to heavy moult (25 to > 50% of moulting feathers) was recorded in all feather regions. The intensity of down moult was greater in males than in females, but no differences between sexes in moult score by c ontour feather region, overall mean moult score, or ADJMOLT were detec ted. Relations between ADJMOLT and body fat (FAT), liver protein (LIVE R), and size-adjusted body mass (ADJMASS), body protein (ADJPROT), and leg and breast muscle protein (ADJLEG and ADJBR, respectively) were n ot influenced by sex, but there was a sex effect on the relation of AD JMOLT to gizzard mass (GIZZWT). ADJPROT and ADJBR were negatively asso ciated with ADJMOLT, whereas female GIZZWT was positively related to A DJMOLT. ADJMASS, ADJLEG, FAT, and LIVER were unrelated to ADJMOLT. Fem ale ruddy ducks were structurally smaller and had less ADJMASS, ADJPRO T, ADJLEG, and FAT than males, but there were no sex-related differenc es in ADJBR. I found no evidence of nutritional stress in postbreeding ruddy ducks, but argue that stress associated with moult in waterfowl is most likely to occur in females, especially small-bodied species t hat are primarily herbivorous.