Foraging microhabitat selection of Spoon-billed Sandpiper in the Upper Gulf of Mottama, Myanmar

Abstract

Spoon-billed Sandpiper (Calidris pygmaea) is Critically Endangered, declining 9% per year since 2009; although important wintering sites have been identified, little is known about why particular sites are selected. The Gulf of Mottama, Myanmar, supports perhaps 60% of the global population in winter. Our objective was to identify macrohabitat and microhabitat characteristics of Spoon-billed Sandpiper foraging locations. We considered 1) location (relative to distance to the main channel of the gulf), 2) temporal patterns (relative to the tide cycle), 3) physical substrate characteristics and 4) possible food sources. Spoon-billed Sandpipers were observed at 26 foraging locations during the study (November 2019-March 2020). The sandpipers were found more frequently on mixed sand-mud substrate, similar to over-wintering sites in Bangladesh, and while it is likely that the mixed sand-mud substrate was generally further from the main channel than the pure sand substrate, presumably due to tidal action, we found no evidence that Spoon-billed Sandpiper locations were associated with the tide cycle. Logistic regression models indicated that foraging locations were associated with shallow surface puddles, compared to random locations. The mixed sand-mud substrate supported more polychaetes relative to crabs or insect larvae, the three most common prey types in our 442 benthos samples used to assess prey availability. Our results reinforce the point that Mottama needs to be protected as an intact functioning estuary and key site for Spoon-billed Sandpiper and other threatened shorebirds. Although we have identified some characteristics of foraging sites associated with Spoon-billed Sandpiper at Mottama, we still lack understanding as to whether and how potential prey is driving site selection and how these characteristics vary among wintering sites.