They then
disappeared over the sea, as suddenly as they had appeared, and have not
since visited the island. Now, in parts of Natal it is believed by some
farmers, though on insufficient evidence, that injurious seeds are
introduced into their grass-land in the dung left by the great flights of
locusts which often visit that country. In consequence of this belief Mr.
Weale sent me in a letter a small packet of the dried pellets, out of which
I extracted under the microscope several seeds, and raised from them seven
grass plants, belonging to two species, of two genera. Hence a swarm of
locusts, such as that which visited Madeira, might readily be the means of
introducing several kinds of plants into an island lying far from the
mainland.
Although the beaks and feet of birds are generally clean, earth sometimes
adheres to them: in one case I removed sixty-one grains, and in another
case twenty-two grains of dry argillaceous earth from the foot of a
partridge, and in the earth there was a pebble as large as the seed of a
vetch. Here is a better case: the leg of a woodcock was sent to me by a
friend, with a little cake of dry earth attached to the shank, weighing
only nine grains; and this contained a seed of the toad-rush (Juncus
bufonius) which germinated and flowered. Mr. Swaysland, of Brighton, who
during the last forty years has paid close attention to our migratory
birds, informs me that he has often shot wagtails (Motacillae), wheatears,
and whinchats (Saxicolae), on their first arrival on our shores, before
they had alighted; and he has several times noticed little cakes of earth
attached to their feet.
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