184 FRANCIS H. HERRICK 



directly or indirectly provides. This great division is provisionally 

 subdivided into (i) individual or independent nests, which with 

 the possible exceptions to be later noticed, are due to the activity 

 of a single pair of birds, and are occupied exclusively by the 

 builders, and (ii) co-operative nests, which are to some extent 

 built and used on a co-operative plan. Aside from certain of 

 the mound builders, which have been placed in a separate sec- 

 tion, and polygamous ostriches, in which a single cock with 

 three or four hens usually unite in the production and care of 

 the offspring, using a common nest, and sometimes producing 

 as many as thirty eggs, the most striking illustrations are pre- 

 sented by the ani {Crotophaga ani) of the West Indies, and 

 possibly by the sociable grosbeak (Philhataerus socins) of South 

 Africa. Unfortunately exact and sufficiently detailed field obser- 

 vations are lacking in these remarkable birds, and no satisfactory 

 analysis of their breeding habits can now be made. In the 

 ani, several females with one or more (?) males occupy, (and 

 presumably unite in building) a large nest w^hich is placed high 

 in trees. Each female contributes her quota of eggs, which are 

 sometimes deposited in tiers and separated by leaves ; the number 

 of eggs, which depends upon the number of females actively 

 interested, according to Scott, as quoted by Sharpe,^^ has been 

 found to reach at least 21. If the habit of treating the eggs, as 

 noted above is correctly reported, it suggests that such a nest may 

 prove to be a composite, or series of superimposed nests, in refer- 

 ence to the activities of the builders. One bird having singly (or 

 jointly) founded the nest and laid her eggs, is followed by another 

 which satisfies her building impulses by adding leaves, laying 

 upon them her own eggs, and so on. The observer, from whose 

 account the preceding facts were drawn, further says: " In 

 the first nest I examined, the eggs were in two distinct layers, 

 separated by a deep bed of dry leaves ; the bottom layer con- 

 sisted of four eggs, and these strange to say, were all infertile." 

 The last remark suggests that the eggs of a given tier are laid 

 by the same bird. 



The great mushroom like or umbrella shaped nests of the 

 sociable grosbeaks or weaver birds have been often described; 

 the aggregate has been found to contain as many as 327 indi- 

 vidual nests, closely agglutinated and built around the branches 



'^Op. cit., p. 321. 



I 



