CONCEALED OR COVERED NESTS 115 



one, we shall find that it prevails much more 

 uniformly in some groups of birds than in others. 



It will perhaps be most convenient to consider 

 first those groups in which the habit of breeding or 

 nesting in timber is most universal. One of the 

 most characteristic of these is the family of Wood- 

 peckers (Picidae). Woodpeckers are almost cosmo- 

 politan in their distribution (with the exception of 

 J\ladagascar and Egypt and the Australian region), 

 being inhabitants of all wooded areas from the Arctic 

 regions to the Equatorial forests. Broadly speaking, 

 their habits are very similar throughout this vast 

 area, and the method of preparing the procreant 

 cradle of one or two species will amply sufSce for 

 the entire group. Probably it is the rule for these 

 birds to bore or excavate their own nesting holes 

 (which are frequently used for years in succession), 

 but in not a few instances ready-made ones are 

 selected, which are in some cases more or less altered 

 to suit the requirements of the Woodpeckers. Almost 

 every kind of timber is selected, and as a rule that 

 which is more or less decayed, even though covered 

 with a shell of sound wood, seems to be preferred. 

 To English readers the nest-holes of the Woodpeckers 

 inhabiting the British Islands are most familiar. 

 Perhaps the best known species is the Green Wood- 

 pecker {Gecinus viridis). The nest-hole of this bird, 

 made, by the way, in almost every kind of tree, is 

 circular, and usually follows a horizontal direction 



