Wild animals have to be constantly on the alert for predators.
On-the-alert Sentence Examples
These latter, like the colonists in the American Far West, had to be constantly on the alert against the attacks of their troublesome neighbours, and they accordingly organized themselves in semi-military fashion.
Mill could now feel that his main work was accomplished; he remained, however, on the alert for opportunities of useful influence, and pressed on with hardly diminished enthusiasm in his search for useful truth.
Besides, he was eternally on the alert.
He returned to the mainland at the head of 200 convicts, and committed further excesses in the Terra di Lavoro; but the French troops were everywhere on the alert to capture him and he had to take refuge in the woods of Lenola.
The herd never feeds without having a sentinel posted on some prominence to give notice of the approach of danger; which is done by stamping on the ground with the forefeet, and uttering a shrill whistling note, thus putting the entire herd on the alert.