Eurasian oystercatchers open bivalves in two distinct ways. Stabbers approach a mussel whose valves are slightly parted, insert the bill and sever the adductor muscle. Hammerers strike the shell, usually at a weak point, until it breaks. A third group specialises in probing soft sediment for worms rather than opening shellfish at all.
The technique shapes the tool. Bill tips wear differently under the two methods, so stabbers carry a chisel-like bill and hammerers a blunter one, and the bill regrows quickly enough that a change of diet changes bill shape within weeks. Young birds learn the method their parents use during an unusually long dependence period, so the specialisation is partly cultural rather than genetic.
The name is a misnomer. Eurasian oystercatchers rarely eat oysters; mussels, cockles and worms make up most of the diet. The species is now listed as Near Threatened, and the interaction between shellfishery removals and oystercatcher survival on wintering estuaries remains a live and contested question.