In the coming year, the Royal Society is entering its 350th year of existence. It was founded on November 28, 1660, as a forum for scientists and philosophers to discuss their work. Since 1665, it has published the journal Philosophical Transactions. To celebrate its anniversary, the Royal Society is posting sixty of the most significant papers from Philosophical Transactions. You can find them at the society's Trailblazing website.
The mode of accomplishing this was very curious. The little animal, with the assistance of its rump and wings, contrived to get the bird upon its back, and making a lodgement for the burden by elevating its elbows, clambered backward with it up the side of the nest till it reached the top, where resting for a moment, it threw off its load with a jerk, and quite disengaged it from the nest. It remained in this situation a short time, feeling about with the extremities of its wings, as if to be convinced that the business was properly executed, and then dropped into the nest again. With these (the extremities of its wings) I have often seen it examine, as it were, an egg and nestling before it began its operations; and the nice sensibility which these parts appeared to possess seemed sufficiently to compensate the loss of sight, which as yet it was destitute of. I afterwards put in an egg, and this, by a similar process, was conveyed to the edge of the nest, and thrown out. These experiments I have since repeated several times in different nests, and have always found the young Cuckoo disposed to act in the same manner.
The singularity of its shape is well adapted to these purposes; for, different from other newly-hatched birds, its back from the scapulae downwards is very broad, with a considerable depression in the middle. This depression seems formed by nature for the design of giving a more secure lodgement to the egg of the Hedge-sparrow, or its young one, when the young Cuckoo is employed in removing either of them from the nest. When it is about twelve days old, this cavity is quite filled up, and then the back assumes the shape of nestling birds in general.
Jenner, E. (1788). Observations on the Natural History of the Cuckoo. By Mr. Edward Jenner. In a Letter to John Hunter, Esq. F. R. S. Philosophical Transactions of the Royal Society of London (1776-1886), 78 (1), 219-237 DOI: 10.1098/rstl.1788.0016