Figure 1.

(a) Experimental procedure. In stage 1, birds are pre-fed then cache foods A and B in trays 1 and 2. In stage 2, birds are pre-fed one food, then allowed to retrieve from tray 1. In stage 3, birds are pre-fed the other food and allowed to retrieve from tray 2. (b) Experimental timetable, pre-feeding orders and counterbalancing. MD, maintenance diet.