Figure 1. Examples of experimental clutches and naturally parasitized nests.

The top images show the range of colours and patterns found in prinia eggs, and the proportions of host and foreign eggs used in rejection trials (ratios of host:foreign eggs). Lines under the eggs indicate groups originating from the same clutch. The bottom two images show naturally parasitized clutches with one cuckoo finch egg (left) or two cuckoo finch eggs (right). Both cuckoo finch and host eggs show extensive variation among individuals. Prinia eggs have fine lines on them that cuckoo finches do not reproduce; surprisingly, hosts do not seem to use this fail-safe ‘signature’ in egg rejection decisions. Such markings make it easy to distinguish host and parasite eggs. Average host egg size for length is 15.63 mm (max=16.98, min=14.63) and breadth is 11.42 mm (max=11.91, min=10.82) from a sample of 40 randomly chosen eggs.