Tlic Behavior of Noddy and Sooly Tcnis. 199 



between the male and the female marked enough to afford a basis for deter- 

 mining sex. But with close observation, the differences in behavior are so 

 marked, at least during the nest-building and egg-laying stages of the nest- 

 ing period, that the following statements, which refer to the division of labor 

 between the two sexes, are fairly accurate. Later on in the work, I found 

 that observation was greatly aided by marking one of the birds with oil paint, 

 and then from the behavior of the marked bird record whether it was the 

 male or the female.^ 



On May 11, the following notes were obtained from a pair of noddies at 

 work upon a nest which had been started a few days previous : 



Both birds work, bringing sticks, sea-weed, shells, and coral. Both birds 

 shape the nest clumsily by pecking and pulling at the sticks. They never 

 weave the sticks so as to form a compact and durable nest. The stick is 

 dropped on the rim, then drawn into position. Frequently, first one bird, 

 then the other sits in the nest and shapes it. In order to do this the bird 

 rises on its feet and depresses its breast and turns round and round. The 

 material is obtained both far and near. Floating sticks and seaweed are 

 gathered from the water. They frequently alight under the nests of other 

 birds and gather up the fallen branches. They even take the material from 

 other nests which are left momentarily unguarded. Frequent fights ensue. 

 The birds work neither steadily nor rapidly; 10, 15, 20 minutes may elapse 

 before either makes a trip. 



On one of the trips the male grasped a large, dead branch which was 

 fast. Another bird came up and also grasped the stick. A fight ensued in 

 which the intruder was worsted. The male next picked up a large stick and 

 attempted to walk out into an open space in order to rise. An obstruction 

 barred the way. The bird, standing on the outside of the barrier, tugged 

 and tugged at the stick, but unavailingly. Finally he stooped under the 

 obstruction, grasped the stick and backed out. This observation is of in- 

 terest in that it shows a rather wide range of instinctive adaptations. Both 

 birds are busily engaged for the next hour. Then the male leaves, while 

 the female remains sitting on a limb near the nest. Two hours later the 

 male returns and feeds the female. - 



On another occasion in watching the transfer of material from one nest- 

 site to another it was found that one bird did all the work ; the other re- 

 mained sitting on a nearby branch. 



Still another observation was made in which it appeared that the male 

 did most of the work. The observation began just after the male had fed 

 the female. The male flies away (4" 16 p. m.), but returns with a fine 

 straw at 4" 18. Leaves and returns with straw at 4"^ 19"". Leaves at 

 4'' 20" ; returns at 4'' 23, bringing no material ; sits on nest for a moment 

 and preens feathers. Leaves at 4'' 26" and at 4'' 27" returns with another 

 straw. Several straws are then brought at intervals of about one minute. 

 On one trip female is sitting in nest. The male returning with straw forces 

 her out, deposits the straw, and shapes the nest. He leaves and returns 

 with a piece of coral. The female then becomes active and brings a small 



' Se.xual behavior gives die most reliable data. 

 "See p. 202 for details. 



