Migration timing influences the responses of birds to food shortage at their refuelling site

Because migration is highly time-constrained and migration timing varies among individuals, the responses of migrants to food shortage at a refuelling site could differ between individuals that arrive early and late at the site. To test this hypothesis, we compared the stopover decision, in terms of occurrence and length of stay (LOS), of radiotagged Great Knots Calidris tenuirostris before (2012) and after (2015) a dramatic decline in food supply at a critical spring final pre-breeding refuelling site in the northern Yellow Sea. The probability of occurrence at the refuelling site was consistent between the two years, whereas the average LOS significantly shortened in the year of food shortage in late-arriving individuals. This suggests migration timing intensifies the influence of food shortage in late-arriving individuals, which might be more sensitive and vulnerable to food shortage at refuelling sites compared with early-arriving individuals.