118 NATURAL HISTORY 



whether the heronry consist of a whole grove or wood, 

 or only of a few trees. 



It gave me satisfaction to find we accorded so well 

 about the Caprimulgus: all I contended for was to 

 prove that it often chatters sitting as well as flying; 

 and therefore the noise was voluntary, and from organic 

 impulse, and not from the resistance of the air against 

 the hollow of its mouth and throat. 



If ever I saw any thing like actual migration, it was 

 last Michaelmas-day. I was travelling, and out early 

 in the morning: at first there was a vast fog; but by 

 the time that I was got seven or eight miles from home 

 towards the coast, the sun broke out into a delicate 

 warm day. We were then on a large heath or common, 

 and I could discern, as the mist began to break away, 

 great numbers of swallows (Hirundines rusticce) clus- 

 tering on the stunted shrubs and bushes, as if they had 

 roosted there all night. As soon as the air became 

 clear and pleasant they all were on the wing at once ; 

 and, by a placid and easy flight, proceeded on south- 

 ward towards the sea: after this I did not see any 

 more flocks, only now and then a straggler. 



I cannot agree with those persons that assert that 

 the swallow kind disappear some and some gradually, 

 as they come, for the bulk of them seem to withdraw at 

 once: only some stragglers stay behind a long while, 

 and do never, there is the greatest reason to believe, 

 leave this island. Swallows seem to lay themselves 

 up, and to come forth in a warm day, as bats do conti- 

 nually of a warm evening, after they have disappeared 

 for weeks. For a very respectable gentleman assured 

 me that, as he was walking with some friends under 

 Merton Hall on a remarkably hot noon, either in the 

 last week in December or the first week in January, he 

 espied three or four swallows huddled together on the 

 moulding of one of the windows of that college. I have 

 frequently remarked that swallows are seen later at 



