1 920.] Study of Nestling Birds. 863 



Owls or Pigeons, it is a fairly general rule to find that 

 the species nesting in deep holes or in completely covered 

 nests (where, of course, no special protective scheme is 

 required) are usually quite naked when hatched, i.e. House- 

 arid Tree-Sparrow, Long-tailed Tit, Magpie, Kingfisher, 

 Woodpeckers, and Swift. When this is not the case, 

 a marked reduction in the density and distribution of the 

 down is generally observable. There also seems to be a 

 tendency for the down-tracts to disappear from all save the 



Text-fio-ures 5 and 6. 



Fig. 5. — Tree - Creeper ( Certhia 

 familiaris), about 7 days old. 



Fig. 6. — Tree -Creeper {Certhia 

 familiaris), about 7 days old ; 

 side view of head. 



more exposed anterior portions of the body in species that 

 attempt to rear a big family in a more or less confined space. 

 A very good example of this may be found in the two forms 

 of Tree-Creepers {^Certhia brachydachjla and C. familiaris). 

 These birds construct a small, but deeply cupped nest, which 

 is generally wedged into a very narrow crevice. In con- 

 sequence of this, the relatively large brood (Tree-Creepers 

 lay from six to nine eggs) always have restricted accommo- 

 dation, and the young birds are almost invariably crowded 

 together in such a way that only their heads are exposed to 

 view. A body-covering of down vrould therefore be useless, 

 but in order to conceal their heads and to obliterate the 

 symmetrical shadows of the nest-cavity, the crown is adorned 

 with a profusion of greyish-black down (figs. 5 & 6). 

 A similar distribution, to which the same explanation may 

 be applied, occurs in the Goldcrest (Ticehurst). In the 



SER. XI. VOL. II. 3 M 



