SUMMARY AND CONCLUSIONS 340 BIBLIOGRAPHY 343 FIGURES IN TEXT FIGURE PAGE 1. The islands of Micronesia. 6 2. The Mariana Islands. 12 3. The Palau Islands. 13 4. The Caroline Islands. 15 5. The Marshall Islands. 16 6. Routes of migration used by shore birds in the Pacific. 34 7. Avifaunal regions of the central Pacific. 43 8. Faunal areas from which Micronesian birds have been derived. 46 9. Routes of dispersal of rails in the Pacific area. 120 10. Variation in length of culmen of _Sterna s. sumatrana_. 159 11. Geographic distribution of _Thalasseus bergii_. 164 12. Geographic distribution of _Gygis alba_ in the Pacific. 177 13. Distribution and dispersal of _Ptilinopus porphyraceus_. 190 14. Distribution and dispersal of _Gallicolumba_ in the Pacific. 204 15. Distribution and dispersal of _Acrocephalus_ in the Pacific. 260 16. Distribution and dispersal of _Myzomela_ in the Pacific. 316 INTRODUCTION Birds in Micronesia comprise the most outstanding animal life of the islands, as far as vertebrates are concerned. No fewer than 206 kinds, belonging to 37 families and 91 genera have been found there. Although this number upon first consideration may seem large, actually any large land mass in the same latitude has many more kinds of birds than does Micronesia. In this connection it is pertinent to recall that the islands of Micronesia are oceanic and have apparently been formed independently of any continental land mass. Thus, animal life found on these islands has reached them by overseas migration, either by some passive means or by individual effort. Zoogeographers have had some difficulty in explaining the presence of snails and other nonflying animals on isolated oceanic islands. Crampton, in his studies of the land snails of the genus _Partula_ at Guam and Saipan (1925:10), writes, "Despite the geological difficulties, the biological findings strongly support the view that the dominant process in this part of Oceania has been one of subsidence and of insular dissection." Although there exists today some question as to how certain forms of life have reached these remote dots of land, the ornithologist has not been much in doubt as to the actual _means_ of arrival of birds. With the exception of six kinds of birds which are definitely known to have been introduced by man, the birds have apparently reached these islands by flying there from somewhere else. The ornithologist is, therefore, concerned with learning