former has a variet}^ of hurrying notes, and sings all 

 night. Some part of the song of the former, I sus- 

 pect, is attributed to the latter. We have plenty of 

 the soft-billed sort, which Mr. Pennant had entirely 

 left out of his British Zoology," till I reminded him 

 of his omission.^ 



I have somewhat to advance on the different 

 manners in which different birds fly and walk; but 

 as this is a subject that I have not enough consid- 

 ered, and is of such a nature as not to be contained 

 in a small space, I shall say nothing further about it 

 at present. t 



No doubt the reason why the sex of birds in their 

 first plumage is so difficult to be distinguished is, as 

 you say, "because they are not to pair and discharge 

 their parental functions till the ensuing spring." As 

 colours seem to be the chief external sexual distinc- 

 tion in many birds, these colours do not take place 

 till sexual attachments commence. The case is the 

 same with quadrupeds, among whom, in their 

 younger days, the sexes differ but little ; but, as they 

 advance to maturity, horns and shaggy manes, beards 

 and brawny necks, &c., strongly discriminate the 

 male from the female. We may instance still further 

 in our own species, w^here a beard and stronger 

 features are usually characteristic of the male sex ; 

 but this sexual diversity does not take place in earlier 



* See Letter XXVI., to Mr. Pennant, August 30, 1769. 



f See Letter LXXXIV., to Mr. Barrington, August 7, 177S. 



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