单项选择题

Why has the kiwi survived while its relatives the moas have become extinct One reason, I think, is that it has adopted nocturnal(夜间活动的) habits. Kiwis are not normally about in the daytime. During the daylight hours they lie up in hiding, where enemies have no hope of finding them. Their coloration protects them; the strange drab(黄褐色的) feathering, so unlike that of most birds, gives them a cloak(伪装)of invisibility while they sleep. And when night falls, out they come to scratch in the ground and find worms and feed to their hearts’ content.
They couldn’t do that so effectively if they didn’t have another peculiarity that I have not mentioned yet. The nostrils(鼻孔) of most birds open high up near the base of the beak(猛禽的嘴), but the kiwi wears his nostrils right near the tip of the long bill. That’s good for a bird that feeds in the ground at night. The kiwi’s .sight is poor at the best of times, but his sense of smell is acute and so is the sense of touch in the tip of that long bill. He can scratch in the forest floor with his eyes closed, and the, delicate sense located at the beak, tip will feel the slightest movement of a worm(蠕虫). Most of those things have an odour(气味) of some kind, which the kiwi can smell better than we can. And when he either feels or smells something worthwhile in the way of food, the delicate bill is ready to pick it up and swallow it.
You see, in spite of his primitiveness, he is peculiarly and efficiently equipped for the particular way of life — better equipped than any of his competitors — and so he is able to keep ahead of them, But every time we, fell a forest tree, or open wooded land for cultivation, we axe reducing the kiwi’s chance of survival, because his undoubted talents axe useful to him only under special conditions, and if those conditions axe not maintained, out he goes like a candle.
The kiwi is very difficult to find during the daylight hours because ______.