26o A HISTORY OF BIRDS 



Instances thereof are seen in the Snipe, Avocet, Black-throated 

 Diver, Herons and Bitterns. Now it is worthy of note that in 

 the Snipe and the Bitterns, at least, these peculiar markings 

 are known to be used for protective purposes. The Bitterns 

 when desiring to conceal themselves adopt a perfectly vertical 

 position, throwing the head and neck upwards and holding the 

 body perfectly still so that the dark lines down the neck har- 

 monise with the dark inter-spaces between the reeds which 

 form its cover. The Snipe reverses this position, holding the 

 head downwards and presenting the longitudinally marked 

 back so that the tail points directly upwards. 



From the aetiological side it must be admitted we have 

 much yet to learn in the matter of these stripes. 



Where both nestling and adult wear a protective plumage, 

 it seems strange that in many cases a distinct livery should be 

 necessary for each stage. But this may be due to the fact that 

 the environment of the nestling is quite different to the normal 

 environment of the adult. The downy young Ringed Plover, 

 for example {^gialitis hiatku/a), is almost white with dark 

 mottlings; the adult is buff coloured above, white below, and 

 barred across the head and breast with black. These bars 

 are apparently protective devices, for while the khaki-coloured 

 body is invisible, the dark bars are conspicuous, but they 

 bear a curious resemblance to mussels, the empty shells of 

 which occur on every tide-wash, where these birds commonly 

 feed. 



But there is no need to expect a very close connection 

 between the two stages in the life-history, for while in many 

 cases the stripes of the downy plumage may well be ancestral, 

 and, therefore, of extreme antiquity, the plumage of the species 

 is necessarily of more recent origin, and is determined by the 

 requirements of the environment amid which it has developed. 



There are yet other peculiarities of nestling birds which 

 demand at least a brief notice in these pages. 



The first of these concern the " egg-tooth," which is a small 

 calcareous, conical mass developed on the tip of the upper jaw 

 during late embryonic life, and is used for the purpose of 

 cutting away the shell ^or the purpose of escape therefrom. 

 As a rule this drops off soon after hatching. In the Ostrich 

 tribe i^PalcEognathiT) the egg-tooth is never so conspicuously 



