In spring and summer the terns are in constant bright evidence over the open water and the sands. The woodpeckers and the sparrows stay with trees or grasses; the terns are birds of the ocean airs and long white shores, their complement and grace. Thousands of terns nest at Tern Island, on the shore of Chatham Harbor, and through the summer months and early fall there are always a great many off Morris Island and Monomoy, diving for fish. They are sharply made, lithe fliers with a nervous excitability that is peculiar to them. Flocks will hover over a stretch of tidal water where schools of small fish are running and they will fairly batter the water, making a loud sound like paddle wheels as they cover it with points of spray. Hundreds, crying harshly, hover some five or six feet up, dropping and rising continually. Many of them dip forward with wings folded slightly, but others, a little higher up, make steeper dives, hovering against the wind, their wings beating hard, to drop, twisting slightly, and then dive with wings back and head down, sharply and precisely. I have thought that terns seldom miss when they have a fish in sight, but during this kind of mass fishing, particularly when they dip forward as if to pick the fish up and try again, it does look like a matter of trial and error. Also, depending on the season, there may be a number of immature birds in the flock that are not as skillful as their elders. The terns are expert performers in every way. They are small and light with strong, angled wings that can carry them over thousands of miles. They have range, persistence, a bright balance that carries them through the mighty and punishing wilderness in which they live. At the same time, that lovely harsh crying excellence in the form of a tern is fragile, even ephemeral. Terns, in the early period of their lives at least, are expendable, like fish. Common terns especially have large breeding colonies that are extremely vulnerable to human encroachment as well as rats, cats, dogs, skunks, and other marauders, and they definitely need protection. Their existence as a race is hazardous under the best of conditions. The sandy islands or peninsulas which they use for nesting sites may be flooded by storm tides in the spring, destroying thousands of eggs or young birds. An adult tern might live to between fifteen and twenty years of age, although their annual mortality is 23 per cent, and their chance of reaching adulthood is fairly slim, tern mortality in the first year being about 92 per cent.