74 
THE NATURAL HISTORY 
[LETT. 
for a week together at Spalding, without ever being told that 
such a curiosity was just at hand. Pray tell me in your next 
what sort of tree it is that contains such a quantity of herons' 
nests ; and whether the heronry consists 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 anything like actual migration, it was last 
Michaelmas Day. I was travelling, and out early in the morn- 
ing : 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) 
clustering 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 southward towards the sea : after 
this I did not see any more flocks, only now and then a 
straggler. 
I cannot agree with those persons who assert that the swal- 
low kind disappear gradually, as they come, for the bulk of 
them seem to withdraw at once : only some few stragglers stay 
behind a long while, and never, there is reason to believe, leave 
this island. Swallows seem to lay themselves up, and to come 
forth in a warm day, as bats do continually 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 wall 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 Oxford than elsewhere : is this owing 
to the vast massy buildings of that place, to the many waters 
round it, or to what else ? 
