Dear Sir,
Before your letter arrived, and of my own accord, I had been remarking and comparing the tails of the male and female swallow, and this ere any young broods appeared; so that there was no danger of confounding the dams with their pulli: and besides, as they were then always in pairs, and busied in the employ of nidification, there could be no room for mistaking the sexes, nor the individuals of different chimneys the one for the other. From all my observations, it constantly appeared that each sex has the long feathers in its tail that give it that forked shape; with this difference, that they are longer in the tail of the male than in that of the female.
Nightingales, when their young first come abroad, and are helpless, make a plaintive and a jarring noise: and also a snapping or cracking, pursuing people along the hedges as they walk: these last sounds seem intended for menace and defiance.
The grasshopper-lark chirps all night in the height of summer.
Swans turn white the second year, and breed the third.
Weasels prey on moles, as appears by their being sometimes caught in mole-traps.
Sparrow-hawks sometimes breed in old crows’ nests, and the kestrel in churches and ruins.
There are supposed to be two sorts of eels in the island of Ely. The threads sometimes discovered in eels are perhaps their young: the generation of eels is very dark and mysterious.
Hen-harriers breed on the ground, and seem never to settle on trees.
When red-starts shake their tails they move them horizontally, as dogs do when they fawn: the tail of a wagtail, when in motion, bobs up and down like that of a jaded horse.