364 ANNUAL. REPORT SMITHSONIAN INSTITUTION, 19 3 



and which consequently leave their nests unprotected are frequently 

 robbed. There is a limit, however, beyond which it does not pay 

 to try to secure material from another bird's nest. Only the looser, 

 partly woven ends may be easily taken. After that the robber may 

 tug and pull, adding her weight to her strength but she gets little 

 or nothing for her labor. 



On one occasion a long fiber streaming from the bill of a returning 

 female was grasped by three other females and, becoming entangled 

 in a limb, was lost to all of them. Thoroughly to understand the 

 method by which a nest is constructed would require closer inspec- 

 tion, and from every side, than I have been able to give, even with 

 the aid of a high-power glass. The foundation of the nest is laid 

 by wrapping long rootlets, tendrils, or fiber about the supporting 

 limb until it is well covered. To this is woven additional material 

 forming a flat piece or apron, 10 or 12 inches in length, its extent 

 depending in part on the nature of the attachment. When the sup- 

 porting limb is more or less horizontal the apron takes shape more 

 readily than when it is perpendicular. Four nests preserved from 

 the tree that was occupied when the laboratory was established, and 

 that subsequently fell, are attached to horizontal limbs and have broad 

 bases or aprons. But the nest tree now occupied, as I have before 

 remarked, offers, as a rule, perpendicular limbs from which an apron 

 is less easily woven. Apparently, therefore, the present tree is less 

 adapted to the needs of Zarhynchus than the one that fell, its prox- 

 imity to the former site having induced the birds to occupy it in 

 spite of its unsuitability. Possibly for this reason the colony does 

 not grow and in time the tree may be abandoned. 



Under the normal method of procedure when the apron or base 

 of the nest is finished an opening or hole three or four inches in 

 diameter is made in its lower part and the base of the ring or loop 

 thus formed becomes the lip of the entrance to the nest. This ia 

 on one side and usually extends from the lip or rim of the opening 

 to the top, or place of the nest's attachment. The formation of 

 this opening is evidently the most difficult part of nest construction. 

 Its base is usually strengthened by the use of additional material and 

 closer weaving. 



In this loop or ring the bird stands working first above and then 

 below. From this stage downward she works inside the lengthening 

 bag which is evidently formed about her body as a mold, until the 

 lower part of the nest is reached when the outline bulges in response 

 to the increased diameter needed for the reception of the true nest. 

 The weaving here is a little closer and the walls of the nest thicker. 



Even when the long sack is nearly completed, but is still open be- 

 low, the builder leaves and enters the nest by way of the door. 

 Entrance is made on the wing with, as the nest is approached, a 



