368 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 



observably. Eecalling that nest building was begun in both the first- 

 named years on January 8, it follows that in these groups of early 

 builders not less than 31 days were required to build the nest bag and 

 line it. I have suggested, however, that with the advance of the 

 season the increased development of the ovaries may induce the 

 builder to finish her work in a shorter time. For example, nest No. 

 17. of group 2, 1927, begun February 7, was believed to have been 

 completed in 23 days, and nest No. 13 of group 1, 1927, begun Febru- 

 ary 5, in 25 days. 



Completed nests vary from 1 foot and 10 inches to 3 feet and 4 

 inches in length, but the greatest diameter of all (always in the bulb- 

 ous base) is 8 inches. Length, as we have seen, may depend on the 

 proximity of the egg-laying period and hence is variable, but the 

 diameter of that part of the bag containing the true nest is fixed by 

 the size of the sitting bird and, therefore, is always essentially the 

 same. 



THE EGGS 



The terminal branch to which nest No. 5, of group 1, 1927, was 

 attached was broken, presumably by a strong wind, on the morning 

 of March 7, and the nest fell. It contained two eggs which 

 apparently constitute a full set for the species. One of the eggs 

 was broken, the other measured 33 by 22 millimeters. In color it 

 is pale blue with numerous irregularly shaped brownish-black marks 

 varying in size from a pin point to a currant and clustering most 

 thickly about the larger end. Both eggs contained embryos which 

 I estimated to be about 12 or 13 days old. My records give the 

 following history for this nest : It was begun January 8 and was first 

 slept in February 13. On February 21 the female entered and left 

 the nest 14 times between 8.33 and 9.25 a. m. February 22 she en- 

 tered and left six times between 8.17 and 9.04. On both days she was 

 accompanied by a male on every journey to and from the nest. The 

 record for the 22d reads : " No. 5 is the only bird of the seven in 

 group 1 who attracts a male, from which I conclude that the other 

 six have laid." February 23 she left the nest only once between 

 8.17 and 9.04 a. m. and was not accompanied by a male. This evi- 

 dence suggests that she began to incubate February 23, or 12 days 

 before the nest fell. I shall have something to say about the 

 subsequent activities of No. 5, the owner of this fallen nest. 



Incubation in group 1, 1927, was believed to begin on February 18, 

 when the owner of nest No. 2 left her nest at 9.54 and returned at 

 9.59; these being her only movements during an hour's observation. 

 On March 7, she carried food to the nest. On the basis of these obser- 

 vations the period of incubation in this instance was 17 days. On 

 March 11, this bird was seen removing excreta from the nest. 



