Bulletin - United States National Museum - si-pddr - Smithsonian ...

246 BULLETIN 133, UNITED STATES NATIONAL MUSEUM
planted about wells and water holes miles from larger groves. In
eastern Uruguay, where groves of palms cover kilometers of low-
land, ovenbirds fairly swarm. There, .though they came familiarly
about houses, they are less domestic, as there is abundance of range
for them, so that instead of being concentrated near houses they
range through the countryside. At San Vicente any alarm was
sufficient to bring ten or a dozen to shriek their disapproval of my
intrusion.
The loud calls of the ovenbird never fail to announce its presence.
One, presumably the male, with bill thrown up and wings drooped,
gives vent to a series of shrieking, laughing calls, with distended,
vibrating throat, and quivering wing tips. At about the middle of
this strange song its mate chimes in with shrill calls of a different
pitch, and the two continue in duet to terminate together. The loud
notes may be audible at half a mile.
Ovenbirds remain paired throughout the year and mated birds
may usually be found near one another. Though they s?ek shelter
in trees they feed on the ground, frequently far distant from cover,
where, with their plump bodies and short tails, they suggest a thrush
in form. Search for a livelihood is a serious affair that absorbs
every attention, so that they have a preoccupied air. as they walk
about in the herbage with nervous hesitant strides and slightly
nodding heads. The calls of a neighbor or a mate are certain to
bring response even from a distance.
The strange, domed, mud nest of this bird is certain to attract at-
tention from the least observant, as it is built in the most conspicuous
situations without the slightest attempt at concealment. Hundreds
ntay be seen without effort during travel in the pampas. The usual
structure averaged 300 mm. long by 200 mm. wide, though the dimensions
varied according to circumstances, some being nearly
globular and others more elongate. A dome-shaped roof with walls
25 to 35 mm. thick was elevated on a level mud platform until it was
entirely arched over with an irregular hole in one side. An inner
wall of curving outline was then constructed leading to the back of
the inclosure at one side. This cut off the nest cavity from the en-
trance hall, and entry to the nest was througli a small opening, with
a raised threshold, below the roof. When the margins of the opening
were rounded off the structure was complete. As the mud used
for building material was mixed with vegetable fibers, grass, or hair,
the whole made a structure of great firmness. When mud was
scarce the birds sometimes utilized fresh cow dung as building material,
making a structure that when dry, was as strong as a model
of papiermache. To examine the interior in any nest it was neces-
sary to cut a hole in it with a heavy knife, as the hand could not be
introduced into the nest cavity through the entrance.