2 26 Papers from the Marine Biological Laboratory at Tortugas. 



tound new in lo seconds. This routine was repeated i6 times, practically 

 an afternoon's work, without the bird adjusting itself perfectly at any time 

 to the new situation. 



I repeated the above tests on 3 other birds which were nesting- out in 

 the open spaces, with absolutely identical results. In other cases I found 

 that the nests could not be moved in any lateral direction for more than 

 a few centimeters without the birds being badly disturbed. As a control test 

 to the above I obliterated several nests and then redug them in the old 

 positions. In no case were the birds disturbed b\- this. 



Experiment III. 



A nest was chosen in an open space, but very close to some bushes. I 

 obliterated the nest as the bird had constructed it, inserted a black pan, 

 filled this with sand, and constructed a nest inside of it. This gave me 

 an opportunity to move the nest upzvard as well as laterally. On return- 

 mg the bird alighted on the nest without showing any signs of disturb- 

 ance. An hour later I came back and pulled the pan out of the sand and 

 put a few sticks under it. The bird returned, but was not disturbed by this 

 slight change. I then drove in four stakes 10 cm. high and mounted the pan 

 thereon. This served to raise the nest upward without disturbing the other 

 relations of the nest. The bird on returning alighted iiniiiediately on nest. 

 The other birds gathered around, craning their necks and peering upward. 

 The bird then stood up and came to the edge of the pan and peered down. 

 This seemed to disturb it and it flew to the ground, but hopped up again 

 immediately, covered the egg and sat there in comfort the rest of the dav. 

 Raising the nest 10 cm. in the air requires almost no adjustment on the part 

 of the bird. On account of a storm on the island, which lasted for 2 days, 

 no further experiments were made at this time on this nest. I next raised 

 this nest 100 cm.; bird alighted innncdiately squarely on top of the nest; 

 did not make a false movement. On craning neck over the edge of the pan 

 a little later, however, became disturbed and alighted on the ground, and 

 remained there for 45 minutes without attempting again to get on nest. I 

 torced bird to fly up. Again alighted on the nest and began to brood the 

 egg in comfort. On my return several hours later it was still sitting quietlv 

 on nest. 



On the second day after this (when this same bird was at the nest 

 again) I lowered the nest back to 10 cm., its first vertical position. On re- 

 turning the bird alighted squarely on the nest, making perfect adjustment. 

 I scared the bird away. On its return the bird again adjusted accuratelv. 

 I next moved the nest back to the height of 100 cm. Bird returned and 

 alighted on egg and adjusted to it before I could get back to my position in 

 the bushes. Adjustment in the vertical plane is made with exceeding 

 rapidity and ease. 



I then moved the nest 100 cm. to the east, leaving it 100 cm. above the 

 ground. Behavior of bird very interesting. Would not alight on nest. 

 Alighted at the former ground position. After a long time flew from the 

 old position and up to new position of nest. Immediately hopped down and 

 began a most peculiar performance. Bird would hover in space, attempting 

 to adjust to the nest in the air at its former position and height. It would 

 then fly away again and come back to the old position and try to alight in 

 space. This was done 20 times. At the end of 20 minutes the bird 



