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.
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.
Cuckoos are abundant, some of them of lovely plumage, also rollers, kingfishers and hornbills.
The reedbeds and tall fen vegetation support nesting sedge and reed warblers as well as numerous cuckoos.
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.