186 BULLETIN 121, UNITED STATES NATIONAL MUSEUM. 



for supporting and balancing the comparatively heavy body, which is scarcely 

 raised above tlie surface on which the bird is moving. On first leaving the nest 

 the adult bird leaps from the ledge and nimbly catches itself on the wing, 

 but sometimes, especially after being irritated or excited, it may fall to the 

 water before taking flight. When once poised in the air, the tropic-bird may 

 be classed with the most graceful of sea birds. They have a very characteristic 

 movement when flying, which is very unlike any other bird I know. 



Mr. Plath (1913) writes: 



They spend nuich time in the air, and may be seen flying in graceful curves, 

 sometimes swooping in a spiral, with half-closed wings, to the surface of the 

 water, and often alighting there after a skim over the waves. In the water they 

 sit very high, with their tails held well above it. They frequently utter their 

 peculiar cry, which varies — sometimes a rasping t-chik-tik-tik or cUk-et-cUk-et ; 

 again, the noise produced by several birds in the air reminds me of the noise 

 of a greaseless axle on a wagon wheel. 



Their manner of flight differs from most sea birds ; the' wings move much 

 more rapidly, and at a distance one might easily mistake them for pigeons, 

 as their long tails are not then conspicuous. Against the blue of the sky their 

 plumage is dazzling; but see them against the dark background of a cliff, and 

 they appear of a beautiful pale green, due to their glossy plumage reflecting 

 the bright emerald of the water below. 



Doctor Gross (1912) adds: 



Among the enemies of the tropic birds are the colored natives, who molest 

 the nests of the birds in spite of the stringent bird laws of the islands. It is 

 probable the eggs collected are used as food. The robbing of nests for such 

 purpose is said to be common in the West Indies. The wood rat (Mus alexan- 

 drinus), however, is responsible for some of the mysterious disappearances of 

 the many eggs I had under observation. On one of my daily rounds to the 

 nests on Two Rock Island I caught one of these rats in the act of sucking an 

 egg. The greedy creature was allowed to finish his meal, after which he was 

 killed and preserved as evidence against his kind. I saw no other rats in the 

 act of molesting eggs, but no doubt they find the tropic-bird eggs a convenient 

 source of food. 



Winter. — During the winter the tropic birds retire from their more 

 northern breeding grounds to the warmer climate of the West Indies 

 and farther south. They spend much of their time on the wing, 

 wandering far out to sea to feed ; but as they must rest occasionally, 

 they return to the islands, where they rest by day and roost at night 

 in the caves and smaller cavities of the limestone cliffs. Mr. Scott 

 (1891) says: 



The birds appear every morning just after the sun is up and are then to be 

 seen in the greatest numbers. By 10 o'clock they have either gone far out to sea 

 to continue feeding or have retired to their roosting places in the cliffs. Their 

 absence is noticeable from about the time in the morning indicated until just 

 before sundown, when a few, not nearly so many as may be observed in the 

 morning, are to be observed flying along outside of the cliffs. The native fish- 

 ermen say that most of the birds return to their roosting places when it is 

 almost too dark to see. 



