Why does nest-mate eviction help a young cuckoo survive?

Nest-mate eviction is a critical survival strategy for young parasitic cuckoos because it eliminates competition for resources within the host's nest.1

Within hours of hatching, the blind and naked cuckoo uses a specialized depression between its shoulder blades to heave host eggs or other nestlings over the rim of the nest. By successfully removing these competitors, the young cuckoo ensures that it receives the full attention and food supply provided by its foster parents. This behavior allows the cuckoo to grow rapidly, often dwarfing its smaller hosts by the time it is ready to fledge.1