140 THE NATURAL HISTORY 



the filth of that sooty atmosphere. Martins are by far the 

 least agile of the four species ; their wings and tails are 

 short, and therefore they are not capable of such surprising 

 turns and quick and glancing evolutions as the swallow. 

 Accordingly they make use of a placid easy motion in a 

 middle region of the air, seldom mounting to any great 

 height, and never sweeping long together over the surface 

 of the ground or water. They do not wander far for 

 food, but affect sheltered districts, over some lake, or 

 under some hanging wood, or in some hollow vale, 

 especially in windy weather. They breed the latest of all 

 the swallow kind: in 1772 they had nestlings on to 

 October the twenty-first, 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 

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

 bourhood, for one day or two, as late as November the 

 third and sixth, 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 district where they are bred, they must undergo vast 

 devastations some how, and some where ; 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. 



I am, etc. 



