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frequently attacked by woodpeckers. It certainly happens very often, 

 but at the same time it is the best proof of the naturalness of these 

 boxes. The natural holes of the woodpecker, the holes, that is to say, 

 which the woodpeckers have themselves made in the tree, are treated 

 in the same way, as may easily be seen in every old wood. The nesting- 

 boxes formerly used were never attacked by woodpeckers, but they 

 were never inhabited by them. 



The enlarging of the openings by squirrels, which has often been 

 noticed, is also to be seen in natural woodpeckers' holes. But these 

 injuries do not render useless either the real or the artificial holes 

 which serve as dwelling-places for other birds, such as tree-creepers, 

 spotted fly-catchers, redstarts, wagtails, robins, wrens, according to 

 the degree of injury and the place where the box is hung. This has 

 been frequently proved at the Seebach experimental station. 



The lining of the openings with tin is in every way objectionable, 

 as the natural appearance of the boxes their chief merit is destroyed, 

 and such boxes are never inhabited by birds. 



(i) Cavities in Walls. 



Numerous birds build in holes in the walls of the old castle at Seebach. 

 These opportunities for building nests, which are so eagerly made use 

 of, are to be increased shortly by the formation of artificial holes in the 

 thick walls, and extensive experiments are to be tried elsewhere. 

 Nesting-places of this description can be made on the principle of the 

 nesting-boxes by means of cement or other mortar.* 



The nesting-places of clay and similar material which were formerty 

 so often sold, and which are unfortunately still to be had, must be 

 distinguished from the holes made in the walls themselves. The latter 

 are not affected by the changes of the weather, owing to the thickness 

 of the walls ; whereas broods that chanced to be hatched in the artificial 

 stone or clay nesting-holes, with their thin walls, were exposed to abrupt 

 changes of temperature, extremes of heat and cold, and were thus 

 destroyed. 



Many birds will not settle in clay holes : woodpeckers, for instance, 

 never do so. 



* Nesting-places of this description have proved very valuable near Cassel. 

 They were occupied by blue tits, crested tits, wrynecks, black and common 

 redstarts, and all the broods were successful. 



