314 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1949 
nests of others of their own kind instead of making new ones for 
themselves, as this prompted him to raise the following argument: 
If the bird laid in disused nests it would only succeed in avoiding the labour 
of building, but would still have to incubate the eggs itself. If on the other hand 
it was successful in slipping into an unguarded Baya nest whence the brooding 
hen had gone (as actually happened on September 18) and in laying its eggs there, 
it would be, quite involuntarily, but with good effect all the same, compelled to 
retire on the return of the legitimate occupant, leaving its egg to be hatched by 
the Baya. Would such a process not tend, in course of time, to develope into, 
and establish, a habit of systematic and voluntary parasitism as has been observed 
in some African weavers? 
In this connection it may be recalled that Lynes (1924, p. 661) found 
that in nesting colonies of several species of African weavers related 
to the Baya, studied by him in the Darfur Province of the Sudan, 
many nests contained one or two extra eggs of the same species as the 
host, but recognizably distinct by virtue of different color or state of 
incubation, in other words, eggs that probably were laid by other 
individuals of the same kind. It seems then, both in Asia and in 
Africa, that not infrequently female weavers, ordinarily using nests 
they have not built themselves, may lay an occasional egg in a nearby 
nest of their own species. 
The Viduinae are, as stated earlier in this paper, intermediate be- 
tween the typical weavers (Ploceinae) and the waxbills (Hstrildinae). 
In many species (perhaps the majority) of the former group, and also 
in a good number of forms of the latter group, the hens breed in nests, 
the actual construction of which has been foreign to their experience 
and their efforts; in many forms of the latter group, and at least some 
members of the former subfamily, the care of the eggs is taken over, 
at least in part, by the cocks. 
The parasitic mode of reproduction occurs, as far as known, in five 
widely separated and quite unrelated families of birds—the ducks, the 
cuckoos, the honey-guides, the weaverbirds, and the hang-nests (cow- 
birds). There can be little doubt that the development of brood 
parasitism has taken place independently in each of these five groups, 
and it is not without significance, or at least suggestive value, that 
this highly aberrant reproduction pattern has developed among the 
small passerine birds (generally considered to be the most highly 
evolved of all the birds) in those two families some of whose members 
have carried the habit of nest building to its highest and most complex 
development. It is all the more noteworthy that in the weaverbirds, 
a larger group than the hang-nests and one with greater diversity of 
behavior patterns, the parasitic habit has developed in two sub- 
families, apparently {independently—the cuckoo finch, Anomalospiza 
imberbis, in the Ploceinae, and in the members of the Viduinae, three 
of which are definitely known to be parasitic, and the rest of which 
