How do oystercatchers open mussels and other shellfish?

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Illustration of a crab plover (Dromas ardeola), showing a slender wading bird with long legs, a long pointed black bill, white head and underparts, and contrasting black wings and back. — Charadriiform Crab plover (Dromas ardeola)

Oystercatchers (family Haematopodidae) employ two primary methods to open mussels, oysters, and other shellfish, depending on the situation:

Hammering: When exploiting a mussel bed, the bird may tear a mussel loose and hammer a hole into its shell to access the soft tissue inside.1
Cutting: If a shellfish is found in the water with its shell already partially open, the oystercatcher drives its knifelike beak into the opening. It then cuts the adductor muscle, which prevents the shellfish from closing its shell again.1

These birds are well-adapted for this behavior, possessing laterally flattened bills with tips that form a vertical blade. They typically attack their prey as the tide ebbs, when the shells are exposed and still partially open.23