156 NATURAL HISTORY OF SELBORNE. 



in 1772 they had nestlings on to October 21st, and are 

 never without unfledged young as late as Michaelmas. 



As the summer declines the congregating flocks increase 

 in numbers daily by the constant accession of the second 

 broods ; till at last they swarm in myriads upon myriads 

 round the villages on the Thames, darkening the face of 

 the sky as they frequent the aits of that river, where they 

 roost. They retire, the bulk of them I mean, in vast flocks 

 together about the beginning of October ; but have ap- 

 peared of late years in a considerable flight in this neigh- 

 bourhood, for one day or two, as late as November 3rd and 

 6th, after they were supposed to have been gone for more 

 than a fortnight. They therefore withdraw with us the 

 latest of any species. Unless these birds are very short- 

 lived indeed, or unless they do not return to the districts 

 where they are bred, they must undergo vast devastations 

 somehow, and somewhere ; for the birds that return yearly 

 bear no manner of proportion to the birds that retire. 



House-martins are distinguished from their congeners by 

 having their legs covered with soft downy feathers down to 

 their toes. They are no songsters ; but twitter in a pretty 

 inward soft manner in their nests. During the time of 

 breeding they are often greatly molested with fleas. 



LETTER XVII. 



RINGMER, near LEWES, Dec. 9th, 1773. 



I RECEIVED your last favour just as I was setting out for 

 this place; and am pleased to find that my monography 



