294 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1949 
general remarks. Birds, as a rule (there are, of course, exceptions), 
go through a fairly definite cycle of behavior patterns during the year, 
and repeat this cycle every year of their adult lives. Very briefly 
stated, the cycle consists, in typical fashion, of the following parts: 
Migration or, in the case of nonmigratory birds such as the weavers, 
the fragmentation, or breaking-up, of “winter,” nonbreeding flocks 
into pairs of birds; the establishment of individual breeding territories 
(the extent and definiteness of which vary in different species) ; court- 
ship and mating; nest building; egg laying; incubation; care of the 
young; and, finally, migration or the return of the individual birds or 
pairs to the “winter” flocks. Each of these parts of the whole cycle 
is subject to great variation, and each may be influenced in its devel- 
opment and expression by its antecedent stages, and each may exert a 
similar influence on its succeeding stages. 
Like any other sequence of events or stages, the undue development 
of any one part may tend to throw out of line one or more of the 
remaining parts. When everything runs smoothly according to 
what may be looked upon as a normal pattern, it is very difficult 
to observe the sequential effects of each part on its successor and it is 
rarely possible to get even vague glimpses or hints of how the per- 
fected whole cycle came to be developed through the ages. It is 
only when something deviates from this normal pattern that we have 
much chance of learning anything of the factors that control or 
influence it. With these general thoughts in mind, it is instructive 
to examine in some detail what has transpired in one family of birds 
with respect to one part of the life cycle, the nest-building habit, 
and, in connection with it, to related portions of the cycle. 
The weaverbirds have been divided into a number of subfamilies 
(the exact number differing in different classifications), which in a 
general way are characterized by different nest-building habits. 
The arboreal, so-called typical weavers (Ploceinae) construct a 
suspended type of woven nest, usually shaped like a ball or a closed 
oval with a lateral or a downward-extending entrance tube or 
“vestibule.” Most of the species of this group are colonial, some- 
times as many as 50 or more nests being built in the same tree, and 
often with no others on any of the surrounding trees for considerable 
distances. On the other hand, some species are quite solitary, like 
Reichenow’s weaver (Ploceus reichenowi), of which usually only one, 
and apparently never more than two pairs nest on the same tree, and 
in those cases where there are two, only one seems to be breeding at 
atime. The instinct to build is, however, very strong in most members 
of this group as farasknown. Thus, Bates (1930, p. 484) noted of the 
hooded weaver (Ploceus cucullatus) in Cameroon that ‘. . . it seems 
to be a necessity of the birds’ nature to be always busy with their 
nest; they will occupy themselves in their spare time with tearing down 
