Protein Reserve Dynamics in Postbreeding Adult Male Redheads

Abstract

-Labile protein reserve dynamics were studied in postbreeding adult male Redheads (Aythya americana) at Lake Winnipegosis, Manitoba, from 1974 to 1977. Changes in tissue masses were related to molt and behavioral activity. Total body protein fluctuated seasonally but tended to increase from breeding to late fall. Redheads did not increase foraging time to meet the nutritional demands of the simultaneous wing molt. Protein Reserve Index (PRI) increased from the late premolt period to the first half of the flightless phase each year. Losses in breast muscle from late premolt to early wing molt were not compensated by the increasing weight of leg muscles. Breast protein may have shifted to growing feathers or other concurrent tissue growth. Breast muscle gained weight over the latter half of the flightless phase in 1977. Changes in locomotor muscle size were related to overall PRI, foraging time, and anticipated seasonal use rather than simply use-disuse phenomena. Non-breeding male Redheads maintained significantly higher PRI from breeding to late molt and appeared to more easily meet seasonal protein requirements than birds which had bred previously. Protein reserves are maintained by many birds, not as a specialized storage product (Fisher 1954) but as muscle sarcoplasm (Kendall et al. 1973), and may be used for breeding (Jones and Ward 1976, Milne 1976, Korschgen 1977), or molt (Hanson 1962, Newton 1968, Hanson and Jones 1976). The timing of accumulation and utilization of protein reserves in waterfowl appears to have evolved with temporal predictability of food supplies, time constraints on foraging, and predation pressure. Arcticnesting geese have adapted to food shortage through almost total reliance upon reserves during nesting (Barry 1962, Ankney and MacInnes 1978, Raveling 1978). Goslings and adult females can thereby take advantage of temporarily abundant food and continuous daylight for rapid growth and reserve replenishment (Harwood 1975). In contrast, most ducks breed at lower latitudes, are smaller, and rely much more on dietary protein (Krapu 1974, 1981; Swanson et al. 1974; Serie and Swanson 1976; Drobney 1982). Heavy predation on nests has led to complete dependence on internal protein for successful reproduction in Common Eiders (Somateria mollissima; Milne 1976). Little is known about mobility of protein reserves outside the breeding season. The simultaneous remigial molt is alluded to as a period of great stress in waterfowl because many species weigh the least at this time (Weller 1957, Hanson 1962, Hanson and Jones 1976). Conversely, Ankney (1979) and Raveling (1979) have shown that female Lesser Snow Geese (Chen caerulescens caerulescens) and Canada Geese (Branta canadensis) are lightest during incubation and Ankney has argued that having less tissue is adaptive during molt because large reserves need not be maintained in view of a highly predictable, proteinsufficient diet. Hanson (1962) attributed leg hypertrophy during molt of Canada Geese to increased use but suggested that breast muscle atrophy results from the transfer of essential sulfur-containing amino acids (cystine, methionine) from temporarily unneeded breast muscle to growing remiges. Hanson and Jones (1976) found that the mass of the leg muscle increases before the flightless phase. They proposed that reciprocal changes in muscle groups do not result from use-disuse phenomenon, but are evolutionary adaptations to the flightless phase. Ankney (1979) suggested that diet of molting Lesser Snow Geese is not deficient in protein, and attributed compensatory changes in muscle groups to use-disuse. Harwood (1977) considered the arctic food supply to be nutrient-poor for Snow Geese and found variations in feeding behavior which were a compromise between maximizing daily protein intake and brood survival. Raveling (1979) concluded that both hypotheses could have validity in explaining similar changes in molting Cackling Geese (B. c. minima). He also suggested that the phenomenon occurs mainly in males because females eat enough to meet protein requirements. At the center of this controversy is the question of whether birds lack protein during molt (Ankney 1979). It is difficult to demonstrate a deficit when average baseline levels are un-