ITS DISTRIBUTION IN SUMMER. 57 



blue expanse of heaven, now hovering near the 

 earth, ready to pounce upon the luckless mouse, 

 and now inspecting the deserted nests of crows 

 and magpies, in order to secure a commodious 

 retreat wherein to perform their approaching in- 

 cubation. Allowing, on an average, four young 

 ones to the nest, there must have been bred here 

 ninety-six windhover hawks last summer : add 

 the parent biixls, and we shall have, in all, one 

 hundred and forty-four. Scarcely five of these 

 birds were seen here from Michaelmas to the 

 latter end of January. 



"The periodical disappearance of the wind- 

 hover from its breeding-place might give rise to 

 much ornithological inquuy ; but I suspect that 

 when every cii'cumstance shall have been duly 

 weighed, we shall still be in the dark with regard 

 to the true cause of its departure. The want of 

 food cannot be supposed to force it away ; for 

 food the most congenial to its appetite is found 

 here in great abundance at the very time when it 

 deserts us. Neither can supposed inclemency of 

 weather be alleged in support of its migration, as 

 the temperature of England is remarkably mild 

 long after the sun has descended into the southern 

 hemisphere.''* 



* " Essays on Natural History," first series, 3rd edi- 

 tion, p. 261. 



D 5 



