VOICES OF THE NIGHT 



only that sings, and for the purpose afore- 

 mentioned. The note of the nightjar, on the 

 other hand, is equally uttered by both sexes, 

 and both also have the curious habit of 

 repeatedly clapping the wings for several 

 minutes together. They moreover share the 

 business of incubation, taking day and night 

 duty on the eggs, which, two in number, are 

 laid on the bare ground without any pretence 

 of a nest, and generally on open commons in 

 the neighbourhood of patches of fern-brake. 

 Like the owls, these birds sleep during the 

 day and are active only when the sun goes 

 down. It is this habit of seeking their insect 

 food only in the gloaming which makes 

 nightjars among the most difficult of birds 

 to study from life, and all accounts of their 

 feeding habits must therefore be received 

 with caution, particularly that which com- 

 pares the bristles on the mouth with baleen 

 in whales, serving as a sort of strainer for 

 the capture of minute flying prey. This is an 

 interesting suggestion, and may even be 

 sober fact ; but its adoption would necessi- 

 tate the bird flying open-mouthed among the 

 oaks and other trees beneath which it finds 

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