ial ten times, but did not build; on
the other 18 occasions her visits were brief and she usually confined
her activities to an inspection of the nest. Twenty of the visits by
the female were made late in the first phase, marking a gradual
transition to her assumption of building responsibility. (The delay by
the female in beginning to build is puzzling; because all evidence
indicates that she helps select the nest-site, I would expect her to
help with the initial building. There seems to be no clear advantage
in her delay in beginning to build.) The courtship and building
activities of the male plus the presence of a partly completed nest
seem to stimulate the female to commence building. Her visits become
more frequent as construction of the suspension apparatus nears
completion. At a time early in the second day the transition has taken
place, and the female becomes the sole worker.

On May 7, 1960, male 2 (1960), at the time unmated, was observed as he
came upon a nest of the previous year. The nest, after a year's
weathering, suggested in appearance perhaps an early second-day nest.
The bird flew to the nest and tugged and wove loose strands of grass
for three minutes. Before leaving the site, the bird sang twice from
different perches. This observation suggests that a partly constructed
nest can elicit nestbuilding behavior, even in an unmated male.

The techniques of building by the male consist primarily of laying
pieces of grass or bark across the fork, or along one of its branches,
and then fastening them in place with pieces of animal silk. Once a
"racket" has been formed, spider egg cases and plant down are emplaced
among the fibers. The male employs weaving, twisting, and pecking
motions of the head to emplace material.

As previously indicated, the female is the principal worker in the
second and third phases of construction. The male infrequently visits
the nest, but regularly visits the nest tree. The molding of the bag
is accomplished by piling leaves, grasses and plant down onto the
suspension apparatus. This material is also bound in with animal silk.
As the amount of material accumulates, the female begins to trample it
and gradually the bag takes shape. When trampling is first attempted,
the nest often fails to support the female and she falls through the
bottom of the nest. Such an occurrence was observed on May 23, 1960,
on three consecutive trips by female 1 (1960), in constructing nest
1-e (1