Cuckoo birds build no nests of their own. Instead, they rely on trickery to raise their young. The female cuckoo lays her eggs in the nest of a host whose eggs are similar in size and color. The host, often a sparrow, cares for the cuckoo's eggs as her own, and usually rears the hatchlings until they reach maturity.
Does this behavior ring a bell? I suspect that something analogous is unfolding in your world. I'm alerting you to the situation so that you will be fully informed as you decide how to proceed.
(P.S. I'm not saying this is a bad thing; just want you to acknowledge the truth.)