His private rooms were turned into a museum. The walls were covered with festoons of birds' eggs, the shelves crowded with fishes, snakes, lizards, and frogs; the chimney displayed stuffed squirrels and opossums, and wherever there was room hung his own paintings of birds. It was the holiday of life for the young lover of nature, and he enjoyed it with good will.

Here the idea of his great work came to him as he was one day looking over his drawings and descriptions of birds. Suddenly, as it seemed to him, though his whole life had led to it, he conceived the plan of a great work on American ornithology. He began his gigantic undertaking as a master in the school of nature wherein he had been so faithful a student, for he now saw with joy that the past, which had often seemed idle, had been in reality rich with labors that were to bear fruit.

He began at once to put his work into scientific form, and nothing better illustrates his energy and ambition than the fact that he entered on it alone and unaided, though none knew better than he the toil and ceaseless endeavor necessary for its completion. Except in a very immature form, American ornithology at that time did not exist; it was a region almost as unknown to human thought as the new world which Columbus discovered. Season after season, from the Gulf to Canada and back again, these winged creatures of the air wended their way, stopping to hatch and breed their young, becoming acquainted with Louisiana orange-groves and New England apple-orchards, now fluttering with kindly sociability round the dwellings of men and again seeking lonely eeries among inaccessible mountain tops, pursuing their course at all times almost without the thought and cognizance of man. It was Audubon who was the conqueror, if not the discoverer of this aërial world of song, of which he became the immortal historian. It was his untiring zeal which gave thus early to American literature a scientific work of such vast magnitude and importance that it astonished the scientists of Europe and won for itself the fame of being the most gigantic biblical enterprise ever undertaken by a single individual. To do this meant a life of almost constant change, and Audubon can hardly have had an abiding place after his first serious beginning. The wide continent became his home and he found his dwelling wherever the winged tribes sought shelter from the wind and storm. His pursuit was often interrupted by occupations necessary for the support of his family, for at his father's death he had given to his sister his share of the estate and so became entirely dependent upon his own efforts for a livelihood; but at all times, no matter what his situation, his heart was in the wild retreats of nature. Travelling through the West and South in search of fortune as well as of specimens his experiences were often disenchanting. At Louisville and New Orleans he would be forced to make crayon portraits of the principal citizens in order to raise the money for family expenses. Again he taught drawing; he served as tutor in private families, and in order to secure funds for the publication of his work he earned $2,000 by dancing lessons, the largest sum he had ever earned. Many business speculations enlisted Audubon's hopes, but all failed utterly. Once he embarked his money in a steam mill, which, being built in an unfit place, soon failed. At another time he bought a steamboat, which, proving an unlucky speculation, was sold to a shrewd buyer who never paid the purchase money. Again he was cheated in the clearing of a tract of timber. But his studies in natural history always went on. When he had no money to pay his passage up the Mississippi he bargained to draw the portrait of the captain of the steamer and his wife as remuneration. When he needed boots he obtained them by sketching the features of a friendly shoemaker, and more than once he paid his hotel bills, and saved something besides, by sketching the faces of the host and his family.

On the other hand, his adventures in search of material for his work were romantic enough to satisfy the most ambitious traveller. From Florida to Labrador, and from the Atlantic to the then unknown regions of the Yellowstone he pursued his way, often alone, and not seldom in the midst of dangers which threatened life itself. He hunted buffalo with the Indians of the Great Plains, and lived for months in the tents of the fierce Sioux. He spent a season in the winter camp of the Shawnees, sleeping, wrapped in a buffalo robe, before the great camp-fire, and living upon wild turkey, bear's grease, and opossums. He made studies of deer, bears, and cougars, as well as of wild turkeys, prairie hens, and other birds. For days he drifted down the Ohio in a flat-bottomed boat, searching the uninhabited shores for specimens, and living the life of the frontiersman whose daily food must be supplied by his own exertions. Sometimes his studies would take him far into the dense forests of the West, where the white man had never before trod, and the only thing that suggested humanity would be the smoke rising miles away from the evening camp-fire of some Indian hunter as lonely as himself.

Once as he lay stretched on the deck of a small vessel ascending the Mississippi he caught sight of a great eagle circling about his head. Convinced that it was a new species, he waited patiently for two years before he again had a glimpse of it, flying, in lazy freedom, above some butting crags where its young were nested. Climbing to the place, and watching like an Indian in ambush until it dropped to its nest, Audubon found it to be a sea-eagle. He named it the Washington Sea Eagle, in honor of George Washington. Waiting two years longer, he was able to obtain a specimen, from which he made the picture given in his work. This is but one example of the tireless patience with which he prosecuted his studies, years of waiting counting as nothing if he could but gain his end.

Some of his discoveries in this kingdom of the birds he relates with a romantic enthusiasm. Throughout the entire work there runs the note of warmest sympathy with the lives of these creatures of the air and sunshine. He tells us of their hopes and loves and interests, from the time of the nest-making till the young have flown away. The freedom of bird life, its happiness, its experiences, and tragedies appeal to him as do those of humanity. The discovery of a new species is reported as rapturously as the news of a new star. Once in Labrador, when he was making studies of the eggers, his son brought to him a great hawk captured on the precipice far above his head. To Audubon's delight, it was that rare specimen, the gerfalcon, which had heretofore eluded all efforts of naturalists. While the rain dripped down from the rigging above, Audubon sat for hours making a sketch of this bird and feeling as rich as if he had discovered some rare gem.

After twenty years the work was published. Every specimen, from the tiny humming-bird to the largest eagles and vultures, was sketched life size and colored in the tints of nature. There were four hundred and seventy-five of these plates, furnishing a complete history of the feathered tribes of North America, for they showed not only the appearance of the birds but represented also the manners and home life of this world of song. The humming-bird poised before the crimson throat of the trumpet flower, the whippoorwill resting among the leaves of the oak, the bobolink singing among the crimson flowers of the swamp maples, the snow-bird chirping cheerily among the snow-touched berries of the holly, were not sketches merely but bits of story out of bird history. So also are those pictures of the swan among the reeds of the Great Lakes, of the great white heron seizing its prey from the waters of the Gulf, and of the golden eagle winging its way toward the distant heights that it inhabits.

The work was published by subscription in London in 1829 under the title, "The Birds of North America." The price was eighty guineas. Later on a smaller and cheaper edition was issued. The work now is very rare. Audubon had the gratification of knowing that his labors were understood and appreciated by the world of science. When he exhibited his plates in the galleries of England and France, whither he went to obtain subscriptions, crowds flocked to see them, and the greatest scientists of the age welcomed him to their ranks. The Birds of America was his greatest work, though he was interested somewhat in general zoölogy and wrote on other subjects.

Audubon died in New York in 1851. The great zoölogist Cuvier called The Birds of North America the most magnificent monument that art has ever erected to ornithology. The Scotch naturalist Wilson said that the character of Audubon was just what might have been expected from the author of such a work, brave, enthusiastic, self-sacrificing, and capable of heroic endurance.