Page:Popular Science Monthly Volume 76.djvu/407

Rh of its nest, if, however, the nest be raised vertically, the bird, but little disturbed, alights upon it, then if after an interval it be lowered, the bird attempts to alight in the air above the nest in the place where the nest was formerly. A slight horizontal movement of the nest causes great confusion in the bird.

Professor Watson caused adult birds to be taken from Bird Key to Havana, 92 miles; to Key West, 66 miles, and to Cape Hatteras 850 miles from Bird Key. Birds liberated at these places returned in a very short time to their nests on Bird Key. The sooty terns returned from Cape Hatteras in five days, and as they probably flew along shore and not by the straight-line route, they must have flown at least 1,081 miles. This is a most striking experiment, for Cape Hatteras is far to the northward of the northern limit of the geographical range of these birds.

Another Tortugas research was that of Professor Reighard, of the University of Michigan, who worked upon the subject of warning coloration.

For a long time Darwin was puzzled by the fact that many animals are conspicuously colored and yet their habits are such that they openly display themselves to the view of all possible enemies. Why, then, were they not exterminated? That brilliant yet modest man, Alfred Russel Wallace, came forward with an ingenious hypothesis, now well known as the theory of warning coloration. He assumed that such conspicuous