Mr. Tegetmeier has informed me of a curious and inexplicable case of correlation, namely, that young pigeons of all breeds, which when mature become white, yellow, silver (i.e. extremely pale blue), or dun-coloured, are born almost naked; whereas other coloured pigeons are born well clothed with down. Mr. Esquilant, however, has observed that young dun carriers are not so bare as young dun barbs and tumblers. Mr. Tegetmeier has seen two young birds in the same nest, produced from differently coloured parents, which differed greatly in the degree to which they were at first clothed with down.
I have observed another case of correlation which at first sight appears quite inexplicable, but on which, as we shall see in a future chapter, some light can be thrown by the law of homologous parts varying in the same manner. The case is, that, when the feet are much feathered, the roots of the feathers are connected by a web of skin, and apparently in correlation with this the two outer toes become connected for a considerable space by skin. I have observed this in very many
specimens of pouters, trumpeters, swallows, roller-tumblers (likewise observed in this breed by Mr. Brent), and in a lesser degree in other feather-footed pigeons.
The feet of the smaller and larger breeds are of course much smaller or larger than those of the rock-pigeon; but the scutellæ or scales covering the toes and tarsi have not only decreased or increased in size, but likewise in number. To give a single instance, I have counted eight scutellæ on the hind toe of a runt, and only five on that of a short-faced tumbler. With birds in a state of nature the number of the scutellæ on the feet is usually a constant character. The length of the feet and the length of the beak apparently stand in correlation; but as disuse apparently has affected the size of the feet, this case may come under the following discussion.
On the Effects of Disuse.—In the following discussion on the relative proportions of the feet, sternum, furcula, scapulæ, and wings, I may premise, in order to give some confidence to the reader, that my measurements were all made in the same manner, and that all the measurements of the external parts were made without the least intention of applying them to the following purpose.
I measured most of the birds which came into my possession, from the feathered base of the beak (the length of beak itself being so variable) to the end of the tail, and to the oil-gland, but unfortunately (except in a few cases) not to the root of the tail; I measured each bird from the extreme tip to tip of wing; and the length of the terminal folded part of the wing, from the extremity of the primaries to the joint of the radius. I measured the feet without the claws, from the end of the middle toe to the end of the hind toe; and the tarsus together with the middle toe. I have taken in every case the mean measurement of two wild rock-pigeons from the Shetland Islands, as the standard of comparison. The following table shows the actual length of the feet in each bird; and the difference between the length which the feet ought to have had according to the size of body of each, in comparison with the size of body and length of feet of the rock-pigeon, calculated (with a few specified exceptions) by the standard of the length of the body from the base of the beak to the oil-gland. I have preferred this standard, owing to the variability of the length of tail. But I have made similar calculations, taking as the standard the length from tip to tip of wing, and likewise in most cases from the base of the beak to the end of the tail; and the result has always been closely similar. To give an example: the first bird in the table, being a short-faced tumbler, is much smaller than the rock-pigeon, and would naturally have shorter feet; but it is found on calculation to have feet too short by .11 of an inch, in comparison with the feet of the rock-pigeon, relatively to the size of the body in these two birds, as measured from the base of beak to the oil-gland. So again, when this same tumbler and the rock-pigeon were compared by the length of their wings, or by the extreme length of their bodies, the feet of the tumbler were likewise found to be too short in very nearly the same proportion. I am well aware that the measurements pretend to greater accuracy than is possible, but it was less trouble to write down the actual measurements given by the compasses in each case than an approximation.
Table I.
Pigeons with their beaks generally shorter than that of the Rock-pigeon, proportionally with the size of their bodies.
| Name of Breed. | Actual length of Feet | Difference between actual and calculated length of feet, in proportion to length of feet and size of body in the Rock-pigeon | |
| Wild rock-pigeon (mean measurement) | 2.02 | Too short by | Too long by |
| Short-faced Tumbler, bald-head | 1.57 | 0.11 | .. |
| " " almond | 1.60 | 0.16 | .. |
| Tumbler, red magpie | 1.75 | 0.19 | .. |
| " red common (by standard to end of tail) | 1.85 | 0.07 | .. |
| " common bald-head | 1.85 | 0.18 | .. |
| " roller | 1.80 | 0.06 | .. |
| Turbit | 1.75 | 0.17 | .. |
| " | 1.80 | 0.01 | .. |
| " | 1.84 | 0.15 | .. |
| Jacobin | 1.90 | 0.02 | .. |
| Trumpeter, white | 2.02 | 0.06 | .. |
| " mottled | 1.95 | 0.18 | .. |
| Fantail (by standard to end of tail) | 1.85 | 0.15 | .. |
| " " " | 1.95 | 0.15 | .. |
| " crested var. " | 1.95 | 0.0 | 0.0 |
| Indian Frill-back " | 1.80 | 0.19 | .. |
| English Frill-back | 2.10 | 0.03 | .. |
| Nun | 1.82 | 0.02 | .. |
| Laugher | 1.65 | 0.16 | .. |
| Barb | 2.00 | 0.03 | .. |
| " | 2.00 | .. | 0.03 |
| Spot | 1.90 | 0.02 | .. |
| " | 1.90 | 0.07 | .. |
| Swallow, red | 1.85 | 0.18 | .. |
| " blue | 2.00 | .. | 0.03 |
| Pouter | 2.42 | .. | 0.11 |
| " German | 2.30 | .. | 0.09 |
| Bussorah Carrier | 2.17 | .. | 0.09 |
| Number of specimens | 28 | 22 | 5 |