2o6 Papers from tJic Marine Biological Laboratory at Tortiigas. 



is reached. R often joins a group of other noddies sunning upon the beach 

 or house-top (preferably the beach) and goes from this place to relieve O. 

 We shall here describe the " sunning reaction " a little more in detail. 



In the brooding period, this " sunning reaction " (mentioned by Thomp- 

 son, Palmer, et aJ.) is engaged in largely (i) by R's before they return to 

 the nest; (2) by O's just leaving the nest, and (3) by birds which, I be- 

 lieve, are not attached to any nest. Figures 27 and 28, plate 11, show the 

 noddies collected near the beach. The house-top, the dock and an old wreck, 

 the top of my experimental cages, etc., were all utilized by the birds for this 

 purpose. Although the reaction is at bottom gregarious (similar to the 

 feeding reaction) the birds are stolidly indifferent to one another's presence. 

 They sit silent, head to the wind, elaborately preening their feathers, pecking 

 first at one toe, then at another. Occasionally when another noddy joins 

 the group a mutual nodding is engaged in which at times for no observable 

 reason ends in a fight. The birds here as elsewhere are silent. It is interest- 

 ing to note that a definite distance is maintained between birds engaged in 

 this activity. The distance is determined. I believe, by the long diameter 

 of the body of the bird — they must have a free space in which to turn. I 

 have seen 10 to 12 birds upon the comb of the roof of the house separated 



