How did foster-parent experiments show that young oystercatchers learn how to open mussels?

Foster-parent experiments have demonstrated that the method young oystercatchers use to open mussels is not genetically determined, but is instead acquired through imitation.

While adult oystercatchers typically open mussels either by inserting their beaks to cut the adductor muscle or by pecking a hole in the shell's weakest point, researchers found that young birds tend to adopt the specific technique employed by their parents. By using foster-parent experiments—where chicks were raised by adults that utilized a different opening habit than their natural parents—scientists observed that the young birds learned to perform the actions they saw their foster parents executing. This confirms that the feeding behavior is a result of observational learning rather than an innate, inherited trait.1