Among birds that have disappeared from the county, the most to be regretted is the bustard, which in the early part of last century was still to be found in the neighbourhood of Royston, although the precise date of its extermination from this part of England is unknown. The bittern, too, is, at the very most, known only as an occasional straggler; but a specimen was shot in a small marshy pond on Harpenden Common some time previous to 1860. The Royston crow, by some naturalists held to be only a form of the common crow, has been named from the Hertfordshire town, though a widespread species throughout many parts of Europe. Neither has extermination been confined to animals. Fern-hunters have in some instances made a clean sweep of certain species of ferns from many districts, if not from the county generally; and nowadays aspleniums, shield-ferns, polypodies, and false maidenhair (_trichomanes_) have completely disappeared from the Harpenden high roads and lanes; the present writer possessing in his garden what he believes to be the sole remaining indigenous specimen of the last-named species. Among localities specially celebrated for birds in the county are Tring reservoirs, where vast flocks of water-birds congregate, especially in winter. Here breeds the great crested grebe; and here, too, was shot in 1901 the only known British example of the white-eyed pochard. The neighbouring downs, as already mentioned, form one of the chief English resorts of the stone-curlew, or thick-knee; a species of especial interest on account of the remarkable manner in which both birds and eggs assimilate to their surroundings. [Illustration: Tring Park] Rare birds, as well as various maritime species driven from their normal resorts by stress of weather, make their appearance occasionally in various parts of the county, but references to very few of such cases must suffice. During the great visitation of sand-grouse (a bird normally characteristic of the steppes of Central Asia) to the British Isles in 1863, some individuals reached this county. In the early part of last century a little auk, or rotche, was taken on the millhead at Wheathampstead during very severe weather; a great northern diver has been seen on Tring reservoir; a pair of storm petrels were killed some five-and-twenty years ago at Hemel Hempstead, where snow-buntings have likewise been seen; while various species of gulls from time to time put in an appearance in winter. Among recent events of this nature the appearance at Harpenden of an immature specimen of the great purple heron is certainly noteworthy. In 1878 the late Mr J. E. Littleboy had recorded 201 species of birds from the county, and a few others have been added since, bringing up the number to 210 in 1902.