326 BULLETIN 195, UNITED STATES NATIONAL MUSEUM 



the nestling still in the remaining piece. In less than a minute she returned and 

 seized the membrane still attached to the shell. As she pulled on the membrane, 

 the nestling was lifted clear of the nest but fell back without injury. On the 

 second attempt it pulled loose and tumbled the young one into the nest. The 

 membrane was quiclily swallowed and the remaining shell carried away. She 

 returned immediately and picked the small bits of shell from the bottom of the 

 nest, devoured them and commenced to brood. The actual process from the time 

 the crack appeared until the last bits of shell were taken from the nest did not 

 exceed 10 minutes. 



At 9: 28 the next morning (July 22) the female partly rose from the nest dis- 

 playing the separating halves of the last egg. The process was practically the 

 same as that previously described. The parent again took the smaller piece 

 of the shell first. She then returned and picked at the remaining piece two or 

 three times and brooded for 12 minutes before any other move was made. At 

 the end of that time she rose in the nest, picked the bird up in the shell and then 

 let it down again. The shell then came away from the nestling and was re- 

 moved, the small pieces being picked carefully from the nest as before. 



In these three instances the hatching process seems to have been the same. 

 In each case it was due to the combined efforts of the parent and the young bird 

 within the egg. In the first case the initial movement may have come from the 

 female while in the last two it originated with the young. In all three the female 

 assisted by pecking at the egg and by removing the broken shell from the nestling 

 much sooner than it would have been able to free itself from the pieces. 



Dr. Gabrielson found that the catbirds brooded the young very 

 closely during the first days of nest life, but when the young became 

 older they were brooded only about 30 percent of the observation time. 

 The conditions of the weather were an important factor in the deter- 

 mination of the time spent by the female in brooding \he young, but 

 in general the brooding time resolved itself into three distinct periods : 



The first period [was] from 4 : 30 a. m. to 7 : 30 a. m. ; the second from 10 : 30 

 a. m. to 2 : 00 p. m. ; and the third from 6 : 30 p. m. until dark. The first period 

 was undoubtedly as a protection against the chill of the early morning. During 

 the second period the sun's rays fell directly into the nest and the brooding at 

 this time was for the protection against the heat. * * * The brooding in 

 the evening was possibly merely preliminary to settling down on the nest for the 

 night and was the most variable of the three. * * * The position assumed 

 in brooding depended on its purpose. In protecting the nestlings from rain or 

 cold the positions were the same. The female settled down on the nest until it 

 was completely covered and the feathers of the breast were well down over the 

 young. It was also noticed that she generally faced the wind. In brooding as 

 a protection from the heat, she stood on the edge of the nest, with her back to the 

 sun, wings spread, feathers of the breast ruffled and mouth open. From this 

 study the brooding time seems to depend on three factors, viz. — temperature, 

 rainfall, and age of the young. The temperature factor will of course be modi- 

 fied by the length of time the nest is shaded by the surrounding vegetation. As 

 the young become older the brooding becomes less intense for heat or cold but re- 

 mains about the same as a protection against rain. 



The catbird is scrupulous in the sanitation of the nest. The ex- 

 creta is rarely allowed to touch the nest but is taken from the young 

 and immediately eaten or removed. During the observations at the 

 nest Dr. Gabrielson states: "The excreta was removed 125 times, 88 



