Not all eggs in a nest hatch at the same time. Some hatched few days after the other and some may take up to a week. In this instant the one that hatched first would be much bigger. During the hot season where food are scare, the one who is bigger in size would eat more and with strength and size can easily force the smaller one out of the nest. One chick left in the nest means more food for another.
Above the bigger size chick left in the nest.
Was lucky to have met me. Later was picked up and put on the nest again.
Most cases it happened during dry season. Where the parents have to fly far for food. During this period feeding will be less frequency making the chicks craving for food and leading to aggressiveness.
So to find few chicks on the floor during such season is uncommon.