I have now, past dispute, made out three distinct species of the
willow-wrens (motacillae 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 the
18th, I 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 of Ray, which he says 'cantat
voce stridula locustae.' Yet this great ornithologist never suspected
that there were three species.
(*Brit. Zool. edit. 1776, octavo, p. 381.)



Letter XX
To Thomas Pennant, Esquire

Selborne, October 8, 1768.