Over the course of the eight years or so that John James Audubon spent in Kentucky, he notes never seeing the Song sparrow. Today, the Song sparrow is as common in Kentucky along the fence rows, in parks, and near forest edges as horses and cattle are seen grazing in the pastures. And it is not as if Audubon was unfamiliar with the Song sparrow when he asks an even tougher question.
“Among the many wonders unveiled to us by the study of nature, there is one which, long known to me, is not the less a marvel at the present moment. I have never been able to conceive why a bird which produces more than one brood in a season, should abandon its first nest to construct a new one, as is the case with the present species; while other birds, such as the Osprey, and various species of Swallow, rear many broods in the first nest which they have made, which they return to after their long annual migrations, repair, and render fit for the habitation of the young brood to be produced. There is another fact which renders the question still more difficult to be solved. I have generally found the nest of this Sparrow cleaner and more perfect after the brood raised in them have made their departure, than the nests of the other species of birds mentioned above are on such occasions; a circumstance which would render it unnecessary for the Song Sparrow to repair its nest. You are aware of the cleanliness of birds with respect to their nests during the whole period occupied in rearing their young. You know that the parents remove the excrements to a distance from them, so long as these excrements are contained in a filmy kind of substance [technically known today as a fecal sac], of which the old bird lays hold with its bill for that express purpose, frequently carrying them off to a distance of forty or fifty yards, or even more. Well, the Song Sparrow is among the cleanest of the clean. I have often watched the young birds leaving the nest; and after their departure, have found it as well fitted for the reception of a fresh set of eggs as the new nest which the bird constructs. I am unable to understand the reason why a new nest is formed. Can you, reader, solve the question?”