188 BULLETIN 121, UNITED STATES NATIONAL MUSEUM. 



loose earth at the bottom of rock shelters so situated that I could walk directly 

 up to them and pick up the birds. Whenever a nest was approached the parent 

 screamed and fouRht viciously, ruflled its feathers and looked very fierce, but 

 made no attempt to escape. They protested with beak and voice when pushed 

 about, but as soon as I went away a few yards they would shuffle back to resume 

 their former position over the egg. The young, even when quite small, were 

 equally fierce in resenting any intrusion. One nest was found on the beach 

 under the edge of some great rocks that had fallen from the adjacent cliff. It 

 was only 5 or 6 feet above high tide and would have been overlooked but for 

 the angry cries of the old bird when she heard me walking over the roof of her 

 habitation. At sunrise the old birds were found sitting side by side at the 

 mouths of their nesting places waiting to enjoy the lirst rays of sunlight. Half 

 an hour later one of each pair started out to sea, while the other resumed its 

 I)lace on the nfest. 



Col, N. S. Goss (1888a) found them nesting on San Pedro Mar- 

 tir Island, in the Gulf of California, where " the birds breed in 

 holes and crevices on the sides of the steep cliffs that overhang 

 the Avater ; man}^ were inaccessible." The nests " were without mate- 

 rial of any kind," the egg being laid upon the bare rock. In tlie 

 Galapagos Islands Mr. Rollo H. Beck (190-i) says that "on Daphne 

 Island they were common ; several of their nests were in small caves 

 in the sandstone cliffs, being quite similar to the nests of duck hawks 

 in the islands along the Lower California coast. Usually they select 

 some crevice among the loose rocks for a nest, although on San 

 Benedicto Island of the Revillagigedos very often a burrow of the 

 wedge-tailed shearwater is used." 



Eggs. — The red-billed tropic-bird, like the other species, lays but 

 one egg, which in shape is short ovate, ovate or a little elongated. 

 What few eggs I have seen resemble eggs of the yellow-billed species, 

 but average a little larger and are more prettily marked, more evenly 

 and clearly speckled or spotted with " livid brown " or " purple 

 drab." Mr. H. H. Bailey (1906) says: "The coloring of a series of 

 eggs in my collection varies from a creamy dirty yellow ground 

 color, spotted with a darker yellow, to a dark red ground color, 

 spotted with a darker red." Certain eggs look very much like eggs 

 of the prairie falcon or duck hawk. 



The measurements of 40 eggs, in various collections, average 56.4 

 by 41.7 millimeters; the eggs showing the four extremes measure 

 63.2 by 46, 63 by 46, 50.5 by 39.5, and 51.5 by 36.5 millimeters. 



Mr. Bailey (1906) says: 



Both birds take turns in incubating and caring for the young, and during 

 this period the bird in the cavity is fed by its mate. The female, and some- 

 times both birds, is found in the cavity for three or four days before the single 

 egg is deposited. While graceful on the wing, this bird is most awkward on 

 its feet, and when alighting to look for a nesting site drags itself along like 

 a bird with both legs broken. * * * Two cases of removing their young 

 happened while I was on White Kock, both of them similar. Two old birds 



