Nesting Behavior of the Yellow Warbler. 59 



wind, heat, cold, and nest location, which help to determine 

 the brooding periods and the length of the same. Then many 

 brooding periods were cut short by the male bringing food. 

 But it was found that the brooding was more intense during 

 the morning, and scattered throughout the rest of the day, 

 according to the wind and the shading of the nest. The 

 length of the brooding periods varied to a great extent, gen- 

 erally ranging from one minute up to between ten and twelve 

 minutes. There were a few periods which exceeded this, the 

 longest being thirty-two minutes, on the afternoon of July 

 5, and twenty-three and twenty-four minutes, on the after- 

 noon of July 7. These long periods occurred when the nest 

 was unprotected from the rays of the sun. 



On July 7 the brooding periods became less in number and 

 more scattered, the parent bird often departing with only a 

 brief inspection. On the day following, and thereafter, 

 brooding was discontinued entirely except during storm ; 

 while the brief inspections continued as before. As the 

 young became stronger and walked around the nest, they 

 stretched imder the shadow of the leaves or even climbed into 

 the branches. 



These observations show a certain adaptability of behavior 

 under natural environment. It was also shown that their 

 behavior could be modified by artificial conditions. Between 

 the hours of 1 :00 p. m. and 5 :00 p. m. the sun shown directly 

 upon the nest, owing to the fact that the tall weeds which 

 normally shaded the nest, were trampled down, in erecting 

 the blind. During this time broad leaved burdocks were 

 hung upon the guy ropes to throw a shadow over the nest- 

 lings. The female did not brood when the nest was thus 

 shaded, unless there was a strong wind. Thus it would seem 

 that the accident of location would have some bearing upon 

 the intensity of brooding. 



During the first days, the female began the brooding in 

 the evening and was also on the nest in the morning before 

 the feeding began. But on the last two days it was not seen 

 which parent commenced the brooding in the evening or 



