A very long period of isolation must have been required to produce the differences so manifestly to be observed, but a few forms seem at rare intervals to have immigrated, and this immigration would appear to be kept up to our own day, as shown by the instance of Zosterops lateralis, which is said to have lately made its first appearance, and to have established itself in the country, as well as by the fact of two cuckoos, Charadriiformes 650 (incl.
Cuckoos are abundant, some of them of lovely plumage, also rollers, kingfishers and hornbills.
The Manchurian crane is common, as also are eagles, cuckoos, laughing doves, &c. Insects abound, owing to the swampy nature of much of the country.
The other birds include parrots, toucans, gaudily coloured cuckoos, lories, swallows, shrikes, sun-birds, kingfishers, weavers, finches, wild pigeons and crows.
Some cuckoos are singular for their habit of using the nests of smaller birds to lay their eggs in, so that the young may be reared by foster-parents; and it has been suggested that the object of the likeness exhibited to the hawk is to enable the cock cuckoo either to frighten the small birds away from their nests or to lure them in pursuit of him, while the hen bird quietly and without molestation disposes of her egg.
The fact that both sexes of the cuckoo resemble the hawk does not necessarily prove this suggested explanation to be false; but if it be true that the smaller passerine birds are duped by the similarity to the bird of prey, it may be that the cuckoos themselves escape molestation from larger hawks on account of their resemblance to the sparrowhawk.
Some observations, however, of Guy Marshall on the inedibility of certain birds suggest that the resemblance between cuckoos a'nd hawks on the one hand and cuckoos and drongos on the other may be susceptible of another explanation in full agreement with the theory of mimicry as propounded by Bates.
It is clearly possible, therefore, that cuckoos which mimic drongos and hawks may be protected from those enemies which find these birds distasteful.
There may also be mentioned 21 cuckoos, I cockatoo, 20 parrots and parakeets, 20 woodpeckers, barbets, broadbills, starlings, orioles, weaver-finches, larks, nuthatches, 28 beautifully coloured sun-birds, and 23 flower-peckers, titmice, shrikes, swallow-shrikes, tailor-birds, thrushes, fruit-thrushes, fairy blue-birds, fire-birds, 42 fly-catchers, 4 swallows, and 5 species of most beautifully coloured ant-thrushes, as well as a large number of birds for which English names cannot be readily supplied.
According to a treatise published by a German physician, Dr Wessel Linden, in 1754, the saline springs at Ffynon-llwyn-y-gog ("the well in the cuckoos' grove") in the present parish of Llandrindod had acquired more than a local reputation as early as the year 1696.
But alas! we do like cowbirds and cuckoos, which lay their eggs in nests which other birds have built, and cheer no traveller with their chattering and unmusical notes.