56 Gross, The Yellow-hilled Tropic-bird. [jan. 



sites which chance to be situated in the particular locahty, rather 

 than to any gregarious or social instinct on the part of the birds. 



The nature of the nesting site varies from that of the open places 

 on the shelf-like ledges to that of the inner end of a narrow and 

 circuitous passage, or the recesses of an obscure cave. In the 

 two latter situations the presence of the adult bird may often be 

 ascertained by inserting a long pole into the opening, which usually 

 brings forth a slirill cry in response to the intrusion. At Tucker's 

 Town nests were found in shallow excavations in the side of a high 

 sand dune which ran along the shore. These cavities, which 

 apparently were made by the birds themselves, were in each case 

 at the base of some herbage, which to a certain degree shielded 

 and protected the bird from the intense heat and light of the sun. 



The height of the nest above the water varies greatly; it ranges 

 from a point just above the high water mark to one situated near 

 the top of the highest cliffs, perhaps 75 or 100 feet above the sea. 

 At Ely's Harbor some of the nests were so low that during an un- 

 usually high tide accompanying a storm, they were overwashed 

 by the waves and filled with heaps of sargassum and other sea 

 weeds. The sargassum is found in many of the lower open nests, 

 where it is deposited by the giant waves during the severe tempests 

 of the winter months. No nesting material is ever collected by the 

 birds, but the single egg is deposited on the bare rocks or else on 

 the mat of sea weeds already present. 



The nests most favorable for study and photography are those 

 which are exposed to view and are open to the light, but unfortu- 

 nately these are the ones most liable to destruction by the elc' 

 ments or by natural enemies. As a consequence nests in shallow 

 but well protected cavities, from which the eggs and the young 

 could l)e easily removed from time to time, were more desirable, 

 being less liable to molestation. Nine such nests located on four 

 of the islands of the sound near to the laboratory on Agar's Island 

 were chosen for daily observations on the growth and development 

 of the young. On Agar's Island a large observation box was con- 

 structed within four feet of a nest, from which more minute ob- 

 servations of the feeding habits could be made. 



The eggs are extremely variable in their coloration and markings. 

 In general they have a chalky white or creamy groundwork thickly 



