Fat reserves and moult-migration overlap in goldcrests, Regulus regulus-A trade-off?

Moult and migration are both recognised as highly energy-demanding activities of birds. I studied moult-migration overlap in migrating goldcrests Regulus regulus to see whether birds might be trading these activities off against each other. I found that in both sexes the size of subcutaneous fat reserves were greater in birds in later stages of moult. This indicates that birds in active moult were either: (1) not able to store as much fat as birds which have completed moult, or (2) that birds in active moult used up their fat reserves quicker than birds that had completed their moult. This suggests that moult-migration overlap is costly, and there exists a trade-off between energy allocated to moult and migratory fat deposits.

Merila, J. 1997, Ann. Zool. Fennici 34: 229-234