A meadowlark on the ground looks not unlike a flicker, but when he flies he shows that the outside feathers of his tail are white. This is as striking a mark as the white spot on the flicker. Many birds have such markings, and it is thought by men who study birds and look for a use in everything, that such marks serve the purpose of "danger signals" or "recognition marks." That by these birds can know each other in the dusk, or that the flash of color will catch the eye, when the bird does not wish to give a call, but to slip away quietly to avoid danger, and at the same time to give notice to other birds to do the same. HIS RELATIONS WITH US XXVIII HOW HE WORKS FOR US MANY times in this book I have spoken of the great value of the services of birds, in helping us destroy insects and weeds that injure our crops. But there is more to be said about it. From morning till night, almost the whole of his life, nearly every bird is working for us. He does not know he is working for us, of course. He is simply hunting for the food he likes, and what is good for young birds to eat. But what he chooses to eat himself, and to feed the young, consists mostly of creatures that destroy our fruit and vegetables, caterpillars that eat the leaves off our trees, worms that get into our apples and berries, beetles that spoil our roses and our potatoes, mice that eat our crops, and all the worms and grubs that gardeners and farmers are all the time fighting. As I have already said, some of the birds like cherries and green peas, and other things we prefer to keep for ourselves. But we should never forget that they have earned, by their work among the worms, all they can take. [Illustration: CEDAR-BIRD] I say this, not merely because I love the birds, and want to have them live and be happy, but because it is true. It has been proved true by scientific men in the service of the United States government. These men have had thousands of birds killed to see what they were eating, and have found out that nearly all the birds they have examined--blackbirds, cedar-birds, blue jays, hawks, owls, even crows--do us more good by the injurious creatures they destroy, than harm by the fruits and vegetables they eat. To this there is, among the small birds, but one exception, the English sparrow, and, of the large ones, only the two hawks and one owl, mentioned on page 53. Chickadees like to eat the eggs of cankerworms; and for a single meal, one of these tiny birds will eat two hundred and fifty eggs, and he will take several meals a day. Now cankerworms destroy our apples. When they get into an orchard in force, it looks, as Miss Merriam says, as if it had been burned over.