HISTORICAL PREFACE xxix. 



sometimes for no obvious reason at all ; the bird that 

 opens its mouth, is rather an appHcable description of 

 Geese and Garmets than otherwise. 



Chapter XVII. treats of a very obscure subject, 

 namely the great mortahty which there certainly is 

 among Gannets, not of nesthng Gannets, a few of which 

 no doubt die in their nests from sunstroke and lack 

 of food, but of rather older birds. The greatest number 

 of deaths appears to take place among the Gannets 

 when they are in the speckled black plumage of their 

 immaturity, and there can be little question that tliis 

 mortality goes on almost entirely between the ages of 

 two months and six months. During that period, there 

 is an interval of four or five weeks when young Gannets 

 get little or no fish- food, and it may be that, being left 

 to provide for themselves, many subsequently die from the 

 effects of this enforced -fast. Possibly the death-rate is 

 equally high among the young of other birds, either about 

 this time, or at some younger age. It is not to be sup- 

 posed that the Gannet is singular in this respect and other 

 sea-birds — e.g. Cormorants and Guillemots — ^immune. If 

 one reflects about the matter, there must be a measure 

 of mortahty dealt out to all species, for if the majority 

 of young birds did not die, the species would in every 

 case increase too fast. Take the House-Sparrow (Passer 

 domesticus) for instance : England would be over-run with 

 them, if they all came to maturity ! 



Dr. P. Chalmers Mitchell, in a paper to be referred to 

 later on, takes this common bird for an example, remarking 



