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v THE PHILOSOPHY OF BIRDS' NESTS 115the nests were built comparatively open, so that the birdwithin was not concealed. 1 The purple martin takes possessionof empty gourds or small boxes, stuck up for its receptionin almost every village and farm in America ;and severalof the American wrens will also build in cigar boxes, with asmall hole cut in them, if placed in a suitable situation. Theorchard oriole of the United States offers us an excellentexample of a bird which modifies its nest according to circumstances.When built among firm and stiff branches the nestis very shallow, but if, as is often the case, it issuspendedfrom the slender twigs of the weeping willow, it is mademuch deeper, so that when swayed about violently by thewind the young may not tumble out. It has been observedalso that the nests built in the warm Southern States aremuch slighter and more open in texture than those in thecolder regions of the north. Our own house-sparrow equallywell adaptshimself to circumstances. When he builds intrees, as he, no doubt, always did originally, he constructs awell-made domed nest, perfectly fitted to protect his youngones ;but when he can find a convenient hole in a building oramong thatch, or in any well-sheltered place, he takes muchless trouble, and forms a very loosely-built nest.Professor Jeitteles of Vienna has described various forms ofnests of Hirundo urbica adapted to different situations, somehaving the form of a semi-ellipsoid placed vertically, with theentrance at one side, others being three-quarters of a sphere,with the entrance in the centre. A nest of Hirundo rusticawas also observed supported on an iron hook in a wall, butnot itself touching the wall. It was quite hemispherical, likethat of a blackbird, a form common in England, whereas theusual form on the Continent is that of a .quarter of asphere. 2The following case of a recent change of habit in nestbuildingwas communicated to me by Mr. Henry Reeks in1870 :"Thirty years ago, and perhaps less, the herring-gullsused to breed on some inland rocks in a large lake called1Popular Science Monthly, vol. vi. p. 481. Quoted by Vice-PresidentE. S. Morse, in Address to American Association for Advancement of Scienceat Buffalo, N.Y., August 1876.8 Ornithologischer Verein in Wien. Mitthelungen des Ausschusses, No. 3,12 Juli 1876. See also Seebohm's British Birds, vol. ii. p. 174.