200 BIRDS OF LA PLATA 
an harmonious performance, and as the voices have 
a ringing, joyous character, it produces a pleasing 
effect on the mind. 
In favourable seasons the Oven-birds begin build- 
ing in the autumn, and the work is resumed during 
the winter whenever there is a spell of mild, wet 
weather. Some of their structures are finished early 
in winter, others not until spring, everything de- 
pending on the weather and the condition of the 
birds. In cold, dry weather, and when food is scarce, 
they do not work at all. The site chosen is a stout 
horizontal branch, or the top of a post, and they also 
frequently build on the roof of a house ; and some- 
times, but rarely, on the ground. The material used 
is mud, with the addition of horsehair or slender 
fibrous rootlets, which make the structure harder 
and prevent it from cracking. I have frequently 
seen a bird, engaged in building, first pick up a 
thread or hair, then repair to a puddle, where it was 
worked into a pellet of mud about the size of a filbert, 
then carried to the nest. When finished the structure 
is shaped outwardly like a baker’s oven, only with 
a deeper and narrower entrance. 
It is always placed very conspicuously, and with 
the entrance facing a building, if one be near, or if 
at a roadside it looks toward the road; the reason 
for this being, no doubt, that the bird keeps a cautious 
eye on the movements of people near it while building. 
and so leaves the nest opened and unfinished on that 
side until the last, and there the entrance is neces- 
sarily formed. When the structure has assumed the 
