The timing of animal migrations is an interplay between migration
programmes and physiological and environmental conditions. The rate of
body store deposition underlies many timing options, with a key
unresolved question being whether the rate of body store deposition and
resource constraints limit advancements in migration departure. To study
limits of deposition on departure timing, we captured red knots
(Calidris canutus islandica) wintering in the Wadden Sea and manipulated
food availability during spring body store deposition and prenuptial
moulting phases, followed by release and automated tracking. With longer
access to food in captivity, birds gained body stores faster and were
heavier and further progressed in prenuptial feather moult, and after
release departed earlier from the Wadden Sea. Our results show
flexibility in migration decisions with an important role for food
availability.