206 
NATURAL HISTORY 
into lower latitudes, as some suppose, in order to enjoy a 
perpetual summer, why do they not return bleached ? Do 
they not rather, perhaps, retire to rest for a season, and at 
that juncture moult and change their feathers, since all 
other birds are known to moult soon after the season of 
breeding. 
Swifts are very anomalous in many particulars, dissenting 
from all their congeners not onl}^ in the number of their 
young, but in breeding but once in a summer ; whereas all 
the other British Hirundines breed invariably twice. It is 
past all doubt that swifts can breed but once, since they 
withdraw in a short time after the flight of their young, and 
some time before their congeners bring out their second 
broods. We may here remark, that, as swifts breed but 
once in a summer, and only two at a time, and the other 
Hirundines twice, the latter, who lay from four to six eggs, 
increase at an average five times as fast as the former. 
But in nothing are swifts more singular than in their 
early retreat. They retire, as to the main bpdy of them, 
by the 10th of August, and sometimes a few days sooner: 
and every straggler invariably withdraws by the 20th, while 
their congeners, all of them, stay till the beginning of 
October ; many of them all through that month, and some 
occasionally to the beginning of November. This early 
retreat is mysterious and wonderful, since that time is often 
the sweetest season in the year. But, what is more extra- 
ordinary, they begin to retire still earlier in the most 
southerly parts of Andalusia, where they can be no ways 
influenced by any defect of heat ; or, as one might suppose, 
defect of food. Are they regulated in their motions with us 
by a failure of food, or by a propensity to moulting, or by a 
disposition to rest after so rapid a life, or by what ? This 
is one of those incidents in natural history that not only 
baffles our researches, but almost eludes our guesses ! 
These Hirundines never perch on trees or roofs, and so 
never congregate with their congeners. They are fearless 
while haunting their nesting places, and are not to be scared 
with a gun, and are often beaten down with poles and 
cudgels as they stoop to go under the eaves. Swifts are 
