Cattle egrets are usually seen foraging close to where cattle are gra…

The correct answer is Option (3) → The moving cattle stir up and flush out insects from the vegetation.

The cattle egret and grazing cattle are a classic example of commensalism: one partner benefits and the other is neither harmed nor benefited. As the cattle move through the grass, they stir up and flush out insects from the vegetation. The egrets catch these insects, which would otherwise be hard to find.

Option (1) The cattle protect the egrets from predators that stay away from them. — Incorrect. Protection from predators is what the clown fish gets from the stinging tentacles of the sea anemone. The egret’s gain from the cattle is food.

Option (2) The egrets feed on the seeds and grass left behind by the cattle. — Incorrect. Egrets feed on the insects disturbed by the cattle, not on seeds or grass left behind.

Option (3) The moving cattle stir up and flush out insects from the vegetation. — Correct. The moving cattle disturb the vegetation and the insects fly out, so the egrets find food easily near them.

Option (4) The egrets warn the cattle about predators coming close to them. — Incorrect. If the egrets helped the cattle, both partners would gain and the interaction would be mutualism. The book treats the cattle as getting no benefit.

NCERT Extract:
Population Interactions – “… (iv) Commensalism: This is the interaction in which one species benefits and the other is neither harmed nor benefited.”
Population Interactions – “… The cattle egret and grazing cattle in close association, a sight you are most likely to catch if you live in farmed rural areas, is a classic example of commensalism. The egrets always forage close to where the cattle are grazing because the cattle, as they move, stir up and flush out insects from the vegetation that otherwise might be difficult for the egrets to find and catch.”