The source of the copper has long been uncertain. In nature the birds are fruiteaters, and their diet in captivity consists of bone meal, zweibach, corn meal, white potatoes, eggs and carrots—foods that are usually assumed to contain no copper; and no copper utensils are used in the preparation of the food. Dr. John Marshall, however, writes me that all the common cereals contain minute quantities of copper; and Dr. Leon A. Ryan, _University of Pennsylvania Medical Bulletin_, June, 1907, states that copper may be found in animal tissues. Dr. E. P. Corson- White has found traces of copper in the bone meal used at the Philadelphia Zoological Garden. The copper in the red color of the touracou’s wing therefore comes from the food. It is probable that a bright and cheerful bird house does not influence the color of birds by the direct action of light on the color as much as indirectly by improving the health and spirits of the birds. Coloration in birds is a very complicated proposition. It depends upon age, sex, season, health, light, heat, moisture, mode of life, and food. No one bird house can combine all the conditions necessary for the retention of natural colors in every species. The desert species from a habitat of intense light and dryness require for their color a different environment from the forest species, from a habitat of shade and moisture. The suppression of sexual feeling in captive birds may influence color. In nature the finest colors are attained by mating birds. It may be said that all animals—except those of nocturnal habit—have a feeling of joy and well-being in fine weather and bright surroundings that reacts favorably on the general health. The variability of the breeding period induced by captivity in many animals may be mentioned with sterility. It was shown some years ago in the Philadelphia Garden by the European brown bear which in one year gave birth on January 16th, and in the following year on July 25th. It is another evidence of the profound effect of captivity on the captive animal. I know of no observations of the effect of captivity on the period of gestation. There is considerable mortality among captive animals from killing of cage-mates. I do not refer to sexual killing, already mentioned, or to fights over a female. Often males, with no females near, cannot be kept together; probably sexual jealousy is at the bottom of it. Antelope and deer are especially inclined to scrap. Even a large enclosure will not save the weaker male; the stronger follows him with horrible persistency, sometimes for days, around and around the enclosure, often at a walk, but always on the offensive, at least during the day; until, careless from weariness, the weaker is caught unawares and finished by a horn-thrust in the side.