| Summary: | Summary 25 1. Herbivorous birds are hypothesized to migrate in spring along a seasonal gradient of plant 26 profitability towards their breeding grounds (green wave hypothesis). For Arctic-breeding 27 species in particular, following highly profitable food is important, so that they can replenish 28 resources along the way and arrive in optimal body condition to start breeding early. 29 30 2. We compared the timing of migratory movements of Arctic-breeding geese on different 31 flyways to examine whether flyways differed in the predictability of spring conditions at 32 stopovers, and whether this was reflected in the degree to which birds were following the 33 green wave. 34 and slope between onsets of spring at consecutive stopovers. These values differed between 42 sites, mainly because of the presence or absence of ecological barriers. Goose arrival at 43 stopovers was more closely tied to the local onset of spring when predictability was higher and 44 when geese attempted breeding that year. 45 46 5. All birds arrived at early stopovers after the onset of spring and arrived at the breeding 47 grounds before the onset of spring, thus overtaking the green wave. This is in accordance with 48 patterns expected for capital breeders: first they must come into condition; at intermediate 49 stopovers arrival with the food quality peak is important to stay in condition and at the 50 breeding grounds early arrival is favoured so that hatching of young can coincide with the 51 peak of food quality. 52 3 53 6. Our results suggest that a chain of correlations between climatic conditions at subsequent 54 stopovers enables geese to closely track the green wave. However, the birds' precision of 55 migratory timing seems uninfluenced by ecological barriers, indicating partly fixed migration 56 schedules. These might become non-optimal due to climate warming and preclude accurate 57 timing of long-distance migrants in the future.
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