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

Abstract

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.

Arriving late and lean at a stopover site is selected against in a declining migratory bird population

“…Although migratory birds may shift to use alternative refuelling sites and even alter migration route when faced with the deterioration of traditional refuelling sites (e.g. Verkuil et al, 2012), great knots exhibit strong refuelling site fidelity despite such conditions (Ke et al, 2019).…”

“…Although migratory birds may shift to use alternative refuelling sites and even alter migration route when faced with the deterioration of traditional refuelling sites (e.g. Verkuil et al, 2012), great knots exhibit strong refuelling site fidelity despite such conditions (Ke et al, 2019). In fact, the extensive loss and degradation of intertidal habitats en route suggest a lack of alternatives for this tideland specialist (Wang et al, 2022; Zhang et al, 2018).…”

Food supplementation as a conservation intervention: A framework and a case of helping threatened shorebirds at a refuelling site

“…Migratory shorebirds often use the same refuelling sites year after year (Verhoeven et al, 2020) and are unlikely to change refuelling sites when facing food shortage, probably due to the time constraints of the migratory journey (Ke et al, 2019). The Saemangeum estuary in South Korea, for example, was previously the most important refuelling site for great knots during northward migration, supporting over 20% of the global population.…”

Residency, recruitment, and stopover duration of hatch-year Roseate Terns (Sterna dougallii) during the premigratory staging period

“…Thus, differences in staging durations could be driven by differential arrival times to the staging grounds. In addition, differences in premigratory condition between terns arriving earlier versus those arriving later in the staging season or potential resource limitations at the staging grounds (Ke et al 2019), such as loafing area, access to foraging grounds, prey abundance, or competition with Common Terns (Duffy 1986) and kleptoparasitic gulls , could mediate hatchyear tern staging duration at Cape Cod. Additional work is needed to investigate hatch-year Roseate Tern condition while on the Cape Cod National Seashore staging grounds, as well as tern habitat use versus availability and interspecies interactions, to determine if this hypothesis is valid; however, we know that Roseate Terns are relatively concentrated in their use of Cape Cod National Seashore staging areas (Trull et al 1999), which lends some support to this idea of staging habitat limitation.…”