The Natural History of Selborne, 1879/Letter 19
LETTER XIX.
Dear Sir, I have now, past dispute, made out three distinct species of the willow-wrens (motacillæ trochili) which constantly and invariably use distinct notes. But at the same time I am obliged to confess that I know nothing of your willow-lark. In my letter of April 18th, I had told you peremptorily that I knew your willow-lark, but had not seen it then; but when I came to procure it, it proved in all respects a very motacilla trochilus, only that it is a size larger than the two other, and the yellow-green of the whole upper part of the body is more vivid, and the belly of a clearer white. I have specimens of the three sorts now lying before me, and can discern that there are three gradations of sizes, and that the least has black legs, and the other two flesh-coloured ones. The yellowest bird is considerably the largest, and has its quill-feathers and secondary feathers tipped with white, which the others have not. This last haunts only the tops of trees in high beechen woods, and makes a sibilous grasshopper-like noise, now and then, at short intervals, shivering a little with its wings when it sings; and is, I make no doubt now, the regulus non cristatus[1] of Ray, which he says "cantat voce stridulâ locustæ."[2] Yet this great ornithologist never suspected that there were three species.