Extended Data Fig. 2: Schematic overview of migrated distance (solid lines) and stored energy (dotted lines) over time in spring, according to two alternative (extreme) hypotheses.

Both hypotheses assume that early- and late-departing individuals have the same fuelling rate and the same net energy expenditure across their migration, that is they generally arrive at the breeding grounds in the same condition. a, Individuals with different departure dates have the same onset of fuelling, and thus different pre-departure fuelling times. Later departure results in higher energy stores at departure and is compensated with less time spent on stopovers, resulting in the same total time spent fuelling and the same arrival. b, Individuals with different departure dates have the same pre-departure fuelling time and are flexible in the onset of fuelling. Energy stores at departure are the same and later departure is not compensated with faster travel between departure and arrival, still resulting in the same total time spent fuelling (through later arrival). Our results support hypothesis a, with departure date being largely compensated with subsequent en route fuelling time across the study species (except brent goose), resulting in similar arrival among early- and late-departing migrations and individuals (Fig. 4a, b; main text).