Notes on the Common Swift in the Bradford district. 113 
of their departure is fixed more by the forwardness of the young 
brood, and by their ability to undertake the long journey, than 
by the state of the weather, or of their food supply at the time 
of leaving. I find that in the finest summers, and consequently 
when there is the largest supply of winged insect food, this 
colony usually breaks up a day or two earlier than in the colder 
and wetter seasons, and they will leave sometimes when there 
is apparently an unlimited supply of food about. Nesting 
appears to be their sole object here, and as soon as this is com- 
pleted their restless and active spirits fall an easy prey to the 
migration ‘ fever.’ 
Several writers have stated that during fine, warm, clear, 
and still nights in June, the male Swifts remain the whole night 
on the wing, while the females are sitting. Certain it is that 
often on such evenings and just before dark, several birds will 
gradually soar and circle higher and higher until they are no 
longer visible. Several years ago I spent some time in watching 
this curious vesper flight with a good field-glass, but each time 
I lost the birds in the darkness before any apparent descent had 
been commenced. However, about a quarter of an hour later, 
by standing beneath the eaves where a part of the colony nested, 
I frequently, quite distinctly, heard the fluttering in the darkness 
of one or more birds against the wall up above me, which con- 
vinced me that it was the return of the birds that I had been 
watching, to their nesting holes for the night. 
Gilbert White states definitely that he has seen Swifts pairing 
in the air. This statement has been greatly ignored by most later 
writers, and some have even doubtedit. I have never witnessed 
this myself, but Mr. Fred Jowett, a careful observer, reports the 
following occurrence: At Saltaire, on May 26th last year, at 
8-20 a.m., he was noticing a pair of Swifts which were flying 
and sailing at a good elevation. Suddenly they appeared to- 
gether as if one bird, slowly descending in a vertical line during 
this time, and shortly after they separated and flew about as 
when first noticed. Mr. Jowett afterwards heard from a gentle- 
man who lives near that he had witnessed exactly the same 
action two mornings before, at the same place, and at about the 
same hour. It may be that this habit is better known than 
I suspect, but that it is not often recorded. 
At this season of the year it is interesting to note with what 
eagerness Swifts will pick up, and take away, any small feather, 
straw, or light substance that is carried into the air by the wind. 
It is easy to discover where they are nesting. During the 
1907 March 1. 
H 
