612 ANIMAL LIFE IN THE YOSEMIIE 



2^ in depth. In some, the mud used is located only in the basal portion ; 

 in others there is a smooth rim of mud at the top. The outside height of 

 a nest depends somewhat on its location. Those nests saddled on large 

 horizontal branches are least in volume. 



The method of construction and the industry of the robin in carrying 

 on the work of nest building may well be shown by direct quotation from 

 one of our field notebooks. 



Yosemite Valley, April 30, 1916. Found a robin engaged in building a nest 12 feet 

 above the ground on a 3 -inch horizontal branch of a big (4-foot) yellow pine. Very 

 exposed situation, without any sheltering foliage. I watched the bird for over half an 

 hour. Its schedule was as follows: 



8:7:25 a.m. Flew to mud at small drainage ditch about 150 yards away. 



8:7:50. Returned with small ball of mud in bill; placed this in bottom of nest, then 

 got in latter (which was deep enough to shelter bird from chin to base of tail), threw 

 its breast forward, tilted up its tail, held its wings well up (but not extended) on back, 

 and ' tamped ' mud into place by forcing breast against wall of nest ; after several thrusts 

 in one direction the bird rotated itself slightly and tamped again. This was kept up 

 until more than one complete revolution had been made. This rounds the nest, and 

 forces the mud into the interstices so that it holds together the grasses, string, etc., 

 which form basis of nest. Mud was noted on breast feathers of bird when it emerged. 



8:13:25. Bird left nest and went toward Yosemite Creek, a different direction from 

 where other mud was obtained. 



;15:55. Eeturned with stringy mud; tamped. 

 ; 17:50. Left nest and went to first source of mud. 



:19:00. Eeturned with moderate sized ball; tamped; lit on nest edge and not 

 on usual twig. 



8:21:00. Off to Yosemite Creek. 



8:23:45. Eeturned with mud evidently containing leaves; tamped. 



8:26:10. Oft" to Yosemite Creek again. 



8:30:05. Eeturned with ma.ss of stringy mud; tamped. 



8:35:45. Off to Yosemite Creek again. 



Several trips were made before I began timing the bird. Often, as it was tamping 

 it would catch a free end of grass at the nest edge and tuck it down in. The tamping 

 and circling serves to make the nest strong, regular, and smooth, so that it can shelter 

 the eggs and young securely. The mud is very wet when gathered, as I found 'by 

 visiting the place where the first lot was obtained. The bird always came directly to 

 the nest, even when, as it approached, I was on the ground and in plain sight between it 

 and the nest. 



This particular robin, as we see, was bringing a fresh lot of material 

 every five to ten minutes, and during the period when it was under obser- 

 vation it worked without a rest. After the nest is completed there is usually 

 an interval of a few days before egg laying commences. This affords time 

 for the mud to dry thoroughly. 



The eggs of the robin are of a uniform deep blue color, with a slight 

 greenish tinge, but without spots of any sort. The shells have a dull sur- 

 face appearance which is characteristic of the eggs of this species. Four 

 eggs are commonly to be found in the nest of the robin; yet we did not 

 see more than 3 young robins in any one brood, within the nest, or out 



