Star Born by Andre Norton

Dalgard's feet touched gravel; he waded cautiously to the bank, where a bridge across the river made a concealing shadow on the water. None of the mermen had accompanied him this far. Sssuri, as soon as his human comrade had started for the storage city, had turned south to warn and rally the tribes. And the merpeople of the islands had instituted a loose chain of communication, which led from a clump of water reeds some two miles back to the seashore, and so out to the islands. Better than any of the now legendary coms of his Terran forefathers were these minds of the spies in hiding, who could pick up the racing thoughts beamed to them and pass them on to their fellows.

Although there were no signs of life about the city, Dalgard moved with the same care that he would have used in penetrating a snake-devil's lair. In the first hour of dawn he had contacted a hopper. The small beast had been frightened almost out of coherent thought, and Dalgard had had to spend some time in allaying that terror to get a fractional idea of what might be going on in this countryside.