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 re- 

 treat wherein to perform their approaching incu- 

 bation. 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 birds, and we shall have, in all, one 

 hundred and forty-four. Scarcely five of these 

 birds were seen here from Michaelmas to the lat- 

 ter end of January. 



"The periodical disappearance of the wind- 

 hover from its breeding-place might give rise to 

 much ornithological inquiry; but I suspect that 

 when every circumstance 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 edition, 

 page 261 



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