COMMON SWALLOW 35 
August I did not meet with a single individual. In 
Buenos Ayres the autumnal migration of the Hirun- 
dines begins about the middle of February, and from 
that date vast numbers of this Swallow are seen 
travelling north, and, in some seasons, they continue 
passing for over a month. One autumn, in April, 
several days after the Swallows had all disappeared, 
flocks of the Common Swallow began again to appear 
flying north, and for ten days afterwards they con- 
tinued to pass in large numbers. They would stoop 
to dip themselves in a pool where I observed them, 
and then alight on the reeds and bushes to rest, and 
appeared quite tired with their journey, rising reluc- 
tantly when approached and some allowing me to 
stand almost within arm’s length of them without 
stirring. I had never before observed any later or 
supplementary migration like this; for as a rule the 
causes which in some years delay the departure of 
birds seem to affect them all alike. Possibly these 
late birds come from some remote district, where 
exceptionally cold weather had retarded breeding 
operations. 
The Common Swallow sometimes lays in a tree, 
in the large nest, previously abandoned, of the 
Lefiatero (Anumbius acuticaudatus). Its favourite site 
is, however, a hole in a wall, sheltered by the over- 
hanging tiles or thatch; for though it does not go 
much into towns, as Azara has remarked, it is very 
domestic, and there is not a house on the pampas, 
however humble it be, but some of these birds are 
about it, sportively skimming above the roof, or 
