While at Filey Brigg, I was lucky enough to get close to some oystercatchers Haematopus ostralegus as they fed on some mussels. These particular oystercatchers were feeding by the ‘hammering’ method, which involves using their thickened beak to smash the shell of their prey to get to the edible insides.
But not all oystercatcher feed in this way, some have slimmer bills they use to wedge between the 2 valves (shells) of the mussel and then prise them open. What is impressive is that this bill shape is not set, and individual oystercatchers can switch between these methods and bill shape in as short a time as 10 days! You can read more about it on Tetrapod Zoology.