One of the first birds I went out to seek--perhaps the most medicinal of all birds to see--was the kingfisher; but he was not anywhere on the river margin, although suitable places were plentiful enough, and myriads of small fishes were visible in the shallow water, seen at rest like dim-pointed stripes beneath the surface, and darting away and scattering outwards, like a flight of arrows, at any person's approach. Walking along the river bank one day, when the place was still new to me, I discovered a stream, and following it up arrived at a spot where a clump of trees overhung the water, casting on it a deep shade. On the other side of the stream buttercups grew so thickly that the glazed petals of the flowers were touching; the meadow was one broad expanse of brilliant yellow. I had not been standing half a minute in the shade before the bird I had been seeking darted out from the margin, almost beneath my feet, and then, instead of flying up or down stream, sped like an arrow across the field of buttercups. It was a very bright day, and the bird going from me with the sunshine full on it, appeared entirely of a shining, splendid green. Never had I seen the kingfisher in such favourable circumstances; flying so low above the flowery level that the swiftly vibrating wings must have touched the yellow petals; he was like a waif from some far tropical land. The bird was tropical, but I doubt if there exists within the tropics anything to compare with a field of buttercups--such large and unbroken surfaces of the most brilliant colour in nature. The first bird's mate appeared a minute later, flying in the same direction, and producing the same splendid effect, and also green. These two alone were seen, and only on this occasion, although I often revisited the spot, hoping to find them again. Now, the kingfisher is blue, and I am puzzled to know why, on this one occasion, it appeared green. I have, in a former work, _Argentine Ornithology_, described a contrary effect in a small and beautiful tyrant-bird, _Cyanotis azarae_, variously called, in the vernacular, "All-colored or Many-colored Kinglet." It has a little blue on its head, but its entire back, from the nape to the tail, is deep green. It lives in beds of bulrushes, and when seen flying from the spectator in a very strong light, at a distance of twenty or thirty yards, its colour in appearance is bright cerulean blue. It is a sunlight effect, but how produced is a mystery to me. In the case of the two green kingfishers, I am inclined to think that the yellow of that shining field of buttercups in some way produced the illusion.