Birds that moult at the wrong time of the year could be disadvantaged, according to a study by scientists at Lund University, Sweden. Birds depend on a full set of feathers for maximum efficiency when flying long distances, but the study shows that moulting has a detrimental effect on their flight performance.
The researchers trained a jackdaw to fly in a wind tunnel and measured different types of drag experienced by the bird. "We expected the bird not to be able to glide at the lowest speeds that it could glide at before moult and our results confirmed this", says Marco Klein Heerenbrink, who is involved in the research.
The results imply the bird could not fully compensate for the missing feathers during moult. This suggests that if a migratory bird departs prematurely before it has fully moulted, it is likely it will need more energy to make the journey and may need more stopovers too.