Phenotypic flexibility in African waterfowl during moult

Background/Question/Methods

The long-term persistence of populations under climate change will depend on their ability to respond favourably to changing environments. Ducks undergo an annual flightless moult and this vulnerable moulting stage will be strongly influenced by environmental change. To better understand the potential for fine-scale adaptation, we investigated the degree to which the body condition, organ mass (pectoral muscle, gizzard, liver and heart) and flight feather growth of Egyptian Geese Alopochen aegyptiaca (actually a duck) living in variable environments showed phenotypic flexibility over the c.37 days of flightless moult. We further explored the generality of our results from the Egyptian Geese study and investigated how body condition and pectoral muscle size of South African Shelduck Tadorna cana, Spur-winged Goose Plectropterus gambensis and Yellow-billed Duck Anas undulata  change during flight-feather moult.

Results/Conclusions

Egyptian Geese mean body mass and condition declined at the start of moult and continued to do so until flight feathers were at least two-thirds grown. Non-moulting Egyptian geese had high pectoral muscle mass which decreased with the onset of moult but started to increase before overall body mass increased. Gizzard mass showed the opposite trend; liver mass increased throughout moult; and heart mass stayed constant. Feathers grew fastest at intermediate lengths. Moulting Spur-winged Geese and South African Shelduck showed a decline in body condition coupled with the atrophy and subsequent hypertrophy of pectoral muscles which is analogous to the phenotypic flexibility displayed in Egyptian Geese.  The high degree of phenotypic flexibility suggests that they will adapt well to local change. Yellow-billed ducks maintained a constant body condition and breast size throughout moult. Body weight and organ mass dynamics during flight feather moult vary among duck species. Each species may have evolved a moult strategy that is best suited to its own annual cycle and the environmental conditions in which it lives.