Murphy (1936:807) states that the principal enemy of the White-tailed Tropic Bird at Bermuda is the introduced rat (Rattus rattus). Introduced rats, particularly Rattus mindanensis on Guam, may prey on the nesting birds. Baker (1946c:404) writes that this rat is a good climber and may spend considerable time in trees. The rat was trapped also in rough coral jungle at the edge of the cliffs, where tropic birds, Micronesian Starlings and other species, may have been nesting.
Little has been recorded concerning the post-breeding season wanderings of these tropic birds in Micronesia. They seemingly spend considerable time at sea, but whether they move as far from their breeding areas as do birds in the Atlantic, as reported by Murphy (1936:803), Baker (1947a:253) and others, is not known.
Murphy (1936:796) notes that the northward distribution of the tropic birds in the Atlantic is dependent on the warm currents of water. In the western Atlantic, the poleward-flowing, warm currents of the Gulf Stream allow for the northern extension of the range of these birds to Bermuda. In the eastern Atlantic, cool currents flowing toward the equator restrict the northern range. The same condition prevails in the eastern Pacific where warm current flowing toward the pole enable the birds to range north to the Bonins and other islands.
The three species of tropic birds known from Micronesia overlap very little in their ranges in this area. The White-tailed Tropic Bird has become firmly established in the western part of Micronesia, but there are only a few records from the extreme eastern part. The Red-tailed Tropic Bird appears to be resident only in the northern Marianas although it has been recorded in the Carolines and Marshalls. Interspecific competition may prevent considerable intermingling of breeding populations in Micronesia, or it may be that each species requires different ecologic conditions.
Sula dactylatra personata Gould
Masked Booby
Sula personata Gould, Proc. Zool. Soc. London, 1846, p. 21. (Type locality, North and northeast coasts of Australia = Raine Island.)
Sula cyanops Finsch, Ibis, 1880, p. 219 (Taluit); Wiglesworth, Abhandl. und Ber. Zool. Mus. Dresden, no. 6, 1890-1891 (1891), p. 72 (Marshalls); Ogilvie-Grant, Cat. Birds British Mus., 26, 1898, p. 430 (Marshalls).
Parasula dactylatra personata Kuroda, in Momiyana, Birds Micronesia, 1922, p. 35 (Marshall Islands); Mathews, Syst. Avium Australasianarum, 1, 1927, p. 232 (Marshall Islands).
Sula dactylatra personata Yamashina, Tori, 7, 1932, p. 407 (Medinilla); Hand-list Japanese Birds, rev., 1932, p. 187 (Medinilla, Marshall Islands); Hand-list Japanese Birds, 3d ed., 1942, p. 208 (Medinilla, Marshall Islands).