More eggs

While the male is watching over his mate, he also keeps watch for predators. Spared lookout duty, the female has more time to eat and put on weight. This enables her to lay more and better-nourished eggs, thus increasing the reproductive performance.

Starving male

The male eats correspondingly less during the mating period. It is believed that this explains why females prefer well-nourished males – they are better at keeping watch.