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 



