“While o’er the cliff the awaken’d Churn-owl hung,
Through the still gloom protracts his chattering song.”
In his 37th Letter to Pennant, the same author refers to it as “the Caprimulgus, or Fern-owl,” and gives an agreeable account of its movements as observed by himself.
Amongst other things he says:—“But the circumstance that pleased me most was, that I saw it distinctly more than once put out its short leg while on the wing, and by a bend of the head deliver somewhat into its mouth. If it takes any part of its prey with its foot, as I have now the greatest reason to suppose, it does these chafers. I no longer wonder at the use of its middle toe, which is curiously furnished with a serrated claw.”
Yarrell has figured the foot, in a vignette to his work on British Birds, in order to show this peculiarity of structure, the use of which has puzzled so many.
The correctness of the view expressed by Gilbert White and confirmed by other authors,[94] has been disputed on the ground that many other birds, as Herons, Gannets, and, I may add, Coursers, have a pectinated claw upon the middle toe, and yet do not take insects upon the wing, or even seize their prey with their feet.
It has been ingeniously suggested that perhaps the serrated claw may be used for brushing away the broken wings and other fragments of struggling insects which doubtless adhere occasionally to the basirostral bristles with which the mouth of this bird is furnished. This is very possible; at the same time it may be observed that Hawks, Parrots, and other birds habitually cleanse the bill and sides of the gape with their feet, and yet have no pectination of the middle claw.
A theory advanced by Mr. Sterland,[95] and endorsed by Mr. Robert Gray,[96] is that since the Nightjar sits lengthwise and not crosswise upon a bough, the serrated claw gives a secure foothold, which in so unusual a position could not be obtained by grasping. But to this theory the objection above made also applies, namely, that many birds, such as Coursers and Thick-knees, have serrated middle claws and yet are never seen to perch.
Some naturalists, and amongst others Bishop Stanley, have surmised that by means of its peculiarly-formed toes, the Nightjar is enabled to carry off its eggs, if disturbed, and place them in a securer spot, but should any such necessity arise, one would think that its large and capacious mouth, as in the case of the Cuckoo, would form the best and safest means of conveyance.
In the young Nightjar at first the peculiarity in question is not observable, and Macgillivray remarked that in a fully-fledged young bird shot early in September, the middle claw had only half the number of serrations which are usually discernible in the adult. He says:—“All birds whose middle claw is serrated have that claw elongated, and furnished with a very thin edge. It therefore appears that the serration is produced by the splitting of the edge of the claw after the bird has used it, but whether in consequence of pressure caused by standing or grasping can only be conjectured.” I have detected some confirmation of this in the case of the common Thick-knee, or Stone Curlew, Œdicnemus crepitans, in some specimens of which I have remarked a very distinct serration of the middle claw, in others only the barest indication of it (the edge of the claw being very thin and elongated); in others again no trace of it.