NESTS AND NEST-BUILDING IN BIRDS 347 



by the arrangement of the materials effected by the bill, as 

 already described. A little green grass was further added to 

 the lining of this nest on the morning of the third day (June i6), 

 when for the four days which followed it appeared to be de- 

 serted, but this was not the case, for though never actually 

 seen in their tree, these robins were detected at a distance on 

 more than one occasion. The first egg was laid at about 3.30 

 p. M., June ig. Towards the close of nest-building operations, 

 as already noticed the intervals of rest between the molding 

 movements became more and more prolonged, until the bird 

 would sit quietly for a longer and longer space, as if resting or 

 trying the "fit.' Now when the need of a nest is urgent these 

 periods of rest are probably further lengthened until the bird 

 remains to lay her first egg. We shall later see how in some 

 cases, as in chipping sparrows, the molding movements seem 

 to shade off into the practice of sitting in the nest, when finally 

 the first egg is laid and incubation begun (see p. 366). In this 

 instance incubation was not regularly established until the ap-* 

 pearance of the second egg which was laid at about noon on the 

 following day (June 20). 



Nest No. 3. — The building of the third nest occupied, accord- 

 ing to my estimate, 23 working hours, and represented 218 

 loads or increments, four-fifths of which were delivered by the 

 female. Over 4,000 molding movements must have been made 

 in shaping the nest-cup. An account of the operations at this 

 nest has been given in another place and only a few facts need 

 be referred to here. Both male and female worked on the first 

 day for a period of about five hours, and at the rate of one load 

 every 3^ minutes ; this acti\'ity gradually slowed down and 

 with the female only engaged, the average rate of delivery 

 on the second day was once in 7I minutes, and on the third 

 once in 13^ minutes. With this abatement of building activity 

 a new habit was gradually developed on the third day, that 

 of sitting quietly in the nest for longer and longer intervals. 

 As was suggested above, these resting intervals possibly become 

 increased until the bird stays to lay her eggs, and finally to in- 

 cubate them, especially when the need of a nest is urgent, but 

 as also noted, several days may elapse when the nest is seldom 

 visited. Many minor details of interest were noticed at this 

 nest, but on the whole the behavior was precisely similar to 



