JOHNSTON: CAYMAN ISLAND AVIFAUNA TABLE 14.-SOME INTER-ISLAND BREEDING DISTRIBUTIONAL PATTERNS. Species Grand Cayman Little Cayman Cayman Brac Phaethon lepturus breeds Sula leucogaster + breeds Sula sula breeds Fregata magnificens + breeds + Dendrocygna arborea breeds breeds Columba leucocephala breeds + breeds Leptotila jamaicensis breeds Amazona leucocephala breeds + breeds Colaptes auratus breeds Centurus superciliaris breeds Myiarchus stolidus breeds Mimocichla plumbea + breeds Vireo altiloquus + breeds breeds Vireo magister breeds Spindalis zena breeds Quiscalus niger breeds breeds + Melopyrrha nigra breeds Totals = 17 11 5 6 Breeding endemic on 7 2 3 only one island + = present, but contemporary breeding unconfirmed ment of propagules . across a given segment of ocean surface is es- sentially constant through time, it follows that larger islands will intercept a larger number of disseminules per unit time." On this basis one would expect Grand Cayman to support a larger resident avifauna (39 species) than the two smaller islands (Cayman Brac 30, Little Cayman 29). This is only a partial explanation, however, because habitat areal expanse and standing water with its concomitant mangrove swamps are also important factors supporting a diversity of bird life. With these ideas in mind, we can initiate an analysis of the inter- esting, interrupted distributional patterns as summarized in Table 14. Phaethon lepturus and Sula leucogaster prefer or require for breeding the high bluffs occurring only on Cayman Brac. Sula sula and Fregata magnificens currently maintain a moderate-sized breeding colony in the landward mangrove fringe of a large shallow lagoon on Little Cayman. The physiognomy of this lagoon site appears similar to those on Grand Cayman, but these birds have not bred on Grand Cayman, at least in historical times. Perhaps quite local prevailing winds and the lack of human disturbances are primary factors in the restricted breeding distri- butions of these two species on Little Cayman. Dendrocygna arborea is evidently confined as a breeding bird to Grand Cayman and Little Cayman where mangrove swamps and ponds are common (cf. Figs. 1, 2, 1975