谢@lcya邀。题主的猜想是对的,这里的owl既不是单数而不是复数,而是已经抽象化了,笼统表示owl这种鸟就行,前面用零冠词,也就是不用冠词。类似于go to school中的school也不一定要具体化为哪一所学校。
如果非要用单数,可以用:
He didn't see the owls swooping past in broad daylight, though people down in the street did; they pointed and gazed open-mouthed asone owl after anothersped overhead.