Abstract
ABSTRACT Competition intensity depends on the number of competitors and the amount of resources available. Coexistence of potential competitors can be enabled through niche differentiation or high resource availability. Using diet analysis, we investigated which of these 2 mechanisms was in play for coexisting shorebirds at a major staging site in the northern Yellow Sea, China, during northward migration in 2011 and 2012. Competition for food at this site is expected to be intense, with an estimated 250,000 migratory shorebirds gathering annually to refuel over a short period. Great Knots (Calidris tenuirostris), Eurasian Oystercatchers (Haematopus ostralegus osculans), and Red Knots (C. canutus) selected mostly the bivalve Potamocorbula laevis, whereas Bar-tailed Godwits (Limosa lapponica) had a broader diet and showed selection for polychaetes, even though most of their biomass intake was of P. laevis. Although all of these shorebirds fed on P. laevis, they showed different size selection and used diff...
Highlights
Animal migration has been described as a primary adaptation to exploit periodic and temporary resources (Harrington et al 2002, Alerstam et al 2003, Dingle and Drake 2007)
Prey Selection Observations of foraging individuals and analysis of droppings confirmed that the bivalve P. laevis was the dominant prey item in the diet of Bar-tailed Godwits, Great Knots, Eurasian Oystercatchers, and Red Knots (Tables 1 and 2), constituting 73–99% of the identified prey items during standardized observations (95–99% of prey swallowed by the knots and Eurasian Oystercatchers were identified; for Bar-tailed Godwits, 68% were identified)
Individual Great Knots and Eurasian Oystercatchers typically fed upon just a single prey type during a 5 min observation period, whereas Bar-tailed Godwits more frequently fed upon multiple prey species (Table 3)
Summary
Animal migration has been described as a primary adaptation to exploit periodic and temporary resources (Harrington et al 2002, Alerstam et al 2003, Dingle and Drake 2007). Intense competition for limited resources is expected at staging sites, given the relatively high concentration of shorebirds, limited time for refueling, and limited resources (Skagen and Oman 1996, Newton 2008). This is true in the Yellow Sea, which is located at the heart of the funnel-shaped landmass of the EAAF (Figure 1A). Little is known about the feeding ecology of shorebirds during stopover along the EAAF, which hinders our understanding of why they select certain places and how they are supported by the resources present
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