Laying is asynchronous: the second egg follows the first by several days, so the elder chick hatches larger and out-competes its sibling for food. In wild nests the younger chick starves or is trampled within about the first week. Across long-term studies of the species, survival of a second chick in the wild has not been documented.
That pattern makes the second egg a redundancy against failure of the first, and it also makes it available. Harvesting programmes in South Africa remove the doomed second egg or chick, rear it artificially and use it to establish new groups, without reducing what the wild nest would have produced anyway.
The species can afford almost no losses. Groups fledge on the order of one chick every several years, birds mature slowly and territories are large, so adult mortality from poisoning, electrocution and persecution is far more damaging than it would be in a fast-breeding bird.