In the red deer studied by Clutton-Brock, males compete with one another to fertilize females. Bigger, stronger males do better. A mother's ability to nurse affects her ability to produce big sons. If she has lots of milk, she can produce larger offspring. A female's dominance status within the herd of females influences her ability to forage and thus her production of milk.
Dominant females produce more sons.
Subordinate females produce more daughters as would be predicted. We don't know the mechanism. Some have tried to apply this same argument to human societies. Powerful clans should produce sons since they can take many wives. Weak families should produce daughters since a son would have little chance of taking a wife.