NOTICES OF NEW BOOKS. 399 



On the South Downs of Sussex and Hampshire, where no 

 bracken happens to interrupt the rolling turf-land for many miles, 

 the nest of the Wheatear frequently escapes detection, owing to 

 the number of holes available, and the difficulty of discovering 

 for certain the particular one selected by the bird. 



Referring to the variation in the number of eggs laid by 

 different species, Mr. Crawford writes : — 



" Where the risks are great, the precautions for the preserva- 

 tion and continuance of the species are exceptional, and there is 

 no better indication and gauge than the contents of the nest. 

 Twelve eggs, roughly, signify double the danger of six. Keeping 

 this in mind as we turn to the sea birds, we" find that the number 

 of eggs is very much smaller than in the case of the land-birds. 

 This holds almost universally, with perhaps the exception of 

 some of the Ducks, whose nesting habits expose them to con- 

 siderable danger. 



V A very common number is three. This holds throughout 

 the Gulls and their immediate kindred. The Terns' nests have 

 three apiece. This is well-nigh the maximum. In the case of 

 the Skuas it is reduced to two. The Divers also lay two. 



" In the case of the Petrels a limit is reached, beyond which 

 further diminution is impossible. Indeed, the unit is so frequent 

 that it may almost be regarded as the typical number. The 

 Guillemot, the Razorbill, the Little Auk, the Puffin, the Shear- 

 water, the Solan Goose, all deposit and sit on one egg at a time ; 

 and they discharge the duty with more than the gravity of a 

 sitting hen on her sixteen. The unit of production must be 

 taken as representing the unit of danger, and means that the 

 sea-birds have so little to fear that, in a majority of cases, one 

 egg is sufficient to maintain or probably slightly increase the 

 species. Five is the usual number found in a land-bird's nest. 

 Four is not uncommon. Three is very rare, occurring with some 

 Owls and Hawks. Two is confined to the Swift and the Nightjar, 

 whose nests are very seldom found ; and the Pigeon, which builds 

 out of reach of many enemies. And one [with land-birds] is un- 

 known. Starting from five with the land-bird, the tendency is 

 upward, not downward ; starting from three with the sea-bird, 

 the tendency is downward, not upward." 



Writing of the Merlin, a characteristic bird on many Scotch 



