Hammer, filter or microphone: How does the Spoon-billed Sandpiper Calidris pygmaea use its bill to feed?

The remarkable and unique bill-shape of the Spoon-billed Sandpiper Calidris pygmaea raises the question as to why such a structure might have evolved. The morphology of the bill was described in detail by Burton (1971) but  at the time there was little information on feeding behaviour. Using information we collected during all stages of the annual cycle of Spoon-billed Sandpipers, we here qualitatively describe six feeding techniques that we observed to be commonly used by the species. Rather unexpectedly, feeding techniques were not strikingly different from other Calidris sandpipers. ‘Sweep-stitching’ was the most distinctive technique but this appears to be an extreme variation of stitching commonly used by other calidrids. We discuss our observations with respect to various hypotheses that have been proposed to explain the bill-shape, and we use our observations of feeding techniques, along with details of the bill’s morphology, to explore possible evolutionary drivers.