No one takes better care of his dress than a bird, and that is why it looks well for a year. Every day, with most birds, it is washed and carefully dried, each feather being passed through the bill, and the whole thoroughly shaken out. At night one may often see robins and catbirds before going to bed, dressing their plumage and shaking off the day's dust. Besides washing and drying the feathers, birds need oil to keep them in best condition. For this purpose they have a little "oil jug," a small gland over the tail, out of which, with the bill, they can squeeze a drop of oil. We often see ducks and geese oiling their feathers before a rain. Water birds, who need a great deal of oil to keep out the wet, have the oil jug very large. Birds seem to know perfectly well the beauty of their plumage. Not only do they try to show it off, as the peacock when he spreads his tail, but they seem to feel shame when their feathers are injured or soiled. One white feather coming in where it does not belong will make a bird very unhappy. He will work and tug at it to pull it out, and often make himself actually ill over the trouble. I had a captive bird who died, I think, from worry and work over a wing feather which persisted in coming in white, and which he insisted on pulling out every time. XXVII DIFFERENT COLORED SUITS A BIRD does not always wear the same colored dress, as I said in the chapter on moulting. A goldfinch, who through the summer wears a gay yellow coat, comes out in the fall in plain olive and black; and the scarlet tanager, who flourishes in the most brilliant red, changes to a quiet green in winter. Besides these, some birds wear at one season a spotted coat, and come out afterwards in one of plain colors. Most of them change by moulting, as I explained, the old feathers dropping out and new ones of another color coming in; or, to speak exactly, the new ones growing out and pushing the old ones off on their tips. But some change color without moulting. All birds moult completely in the autumn, many moult partially in the spring, and some, as I said, change without moulting. This last change of color is made partly by fading, and partly by breaking off the tips of the feathers, or what is called "abrasion." This is a curious process. I told you something about it in chapter vii. Certain feathers have edges different in color from the rest; as, for example, a black feather with tips of yellow. While the feathers are new and perfect, as they lie over each other like shingles on a roof, only the edges show, and these being yellow, the bird appears to be dressed in yellow. But the yellow tips are not so strong as the rest, and they break or wear off, or are pulled off in the spring. What is strange, they break exactly where the black begins. So as soon as the yellow is off, the black shows, and behold, the yellow bird suddenly becomes a black bird.