"In favourable seasons, the Oven-birds begin building in the autumn," Hudson tells us, "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 depending 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 a cornice or the roof of a house; and sometimes, but rarely, on the ground. The material used is mud, with the addition of horse hair 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 towards the road; the reason for this being, no doubt, that the bird keeps a continuous 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 then the entrance is necessarily formed. When the structure has assumed the globular form with only a narrow opening, the wall on one side is curved inwards, reaching from the floor to the dome, and at the inner extremity an aperture is left to admit the bird to the interior or second chamber, in which the eggs are laid. A man's hand fits easily into the first or entrance chamber, but cannot be twisted about so as to reach the eggs in the interior cavity, the entrance being so small and high up. The interior is lined with dry soft grass, and five white pear-shaped eggs are laid. The oven is a foot or more in diameter, and is sometimes very massive, weighing eight or nine pounds, and so strong that, unless loosened by the swaying of the branch, it often remains unharmed for two or three years. A new oven is built every year, and I have more than once seen a second oven built on the top of the first, when this has been placed very advantageously, as on a projection and against a wall."[102] [102] P. L. Sclater and W. H. Hudson, _Argentine Ornithology_, 1888, vol. i. pp. 168, 169. See also Burmeister, "Ueber die Eier und Nester einiger brasilianischen Voegel," _Cabani's Journal fuer Ornith._, 1853, pp. 161-177.