Avian Community, Climate, and Sea-level Changes in the Plio-Pleistocene of the Florida Peninsula

---Eleven previously unidentified fossil avifaunas from Pliocene and Pleistocene localities in the Florida peninsula are presented, within which are included the description of a new species of anhinga (Anhinga beckeri), woodcock (Scolopax hutchensi), and pygmy-owl (Glaucidium explorator), and a new genus and species of condor (Aizenogyps toomeyae). The paleospecies Milvago readei, Dorypaltus prosphatus, and Protocitta dixi are considered to be synonymous with the living taxa Milvago chimachima, Vanellus chilensis, and Pica pica, respectively. These 11 avifaunas supplement the existing record of fossil birds from Florida that collectively provide a unique chronology of ofiginations and extinctions of 239 extinct and extant taxa during a climatically dynamic period that began approximately 2.5 million years ago (Ma). Topographic and bathymetfic maps of the peninsula are used with Geographic Information Systems software to model and correlate sea-level changes with the location and age of major fossil sites, the avian chronology, and presumed primary habitat of each represented taxon. These analyses indicate range expansions of Neotropical, western North American, and continental forest birds into the Florida peninsula during glacial stages, and the isolation, extirpation, or extinction of many of these taxa during interglacial stages. The relatively rapid climatic cycles of the Plio-Pleistocene, combined with the low topography of the peninsula, caused significant loss of wetland habitat during interglacial marine transgressions, especially in southern Florida. This habitat reduction probably accounted for extinctions of many wetland birds, especially those with relatively small body-size, in the late Pliocene. Additional extinctions recorded in the early Pleistocene resulted in a gradual loss of species richness in these communities by the end of the Pleistocene, when modern wetlands were established. Climatic events in the Pleistocene influenced terrestrial communities with the periodic formation and fragmentation of the Gulf Coast corridor, a mosaic of dry, thorn-scrub, savannah, wetlands, and hammocks, that united Neotropical regions to the south with western North America and the Florida peninsula. This corridor developed with the emergence of the shallow continental shelf in the Gulf of Mexico during glacial stages, which in some cases more than doubled the land area of the peninsula and allowed numerous species of mammals, birds, reptiles, and plants to extend their ranges into Florida. Fragmentation of this corridor during interglacial stages caused loss of species richness, probably from loss of habitat heterogeneity in the peninsula. Unlike wetland communities, modern terrestrial communities did not develop until the early Holocene, after the last fragmentation of the corridor and extinction event at 0.01 Ma. Fossil passefine remains suggest that North American continental migration patterns began developing in the peninsula in the late Pliocene, and were fully established by the late Pleistocene, but Neotropical migration patterns may not have developed until the early Holocene. The chronology presented here provides a model of avian biogeography and community development in the Florida peninsula during the ice ages that can be tested with future paleontological research. E-mail: emslies@uncwil.edu. 2 ORNITHOLOGICAL MONOGRAPHS NO. 50 Those who are unfamiliar with the geology of Florida are often surprised to learn of the excellent fossil record of vertebrates known from this state. This record includes the most complete chronology of extinct and extant birds in the Neogene of North America. The avian record beginning 2.5 million years ago (Ma), from the initiation of the ice ages in the late Pliocene to the end of the last major glaciafion (the Wisconsinan) in the late Pleistocene at 0.01 Ma, is particularly well known from dozens of localities that span this period and from the extensive research that has been completed on fossil birds in Florida by Dr. Pierce Brodkorb and his students since 1952 (see Campbell 1992). This monograph is a culmination of more than 14 years of research by the author on Plio-Pleistocene birds in the Florida peninsula. Here, I present the systematic paleontology of avifaunas recovered from four new and seven previously described fossil localities that includes the description of one new genus and four new species, and the identification of 23 extant and three extinct species previously unreported as fossils from Florida. I use this extensive addition to Florida's fossil record with data from numerous previously published avifaunas, with certain modifications, to develop a 2.5 million-year chronology of extant and extinct birds in the peninsula. I compare this avian chronology with the glacial and interglacial stages that caused sea-level changes during the Plio-Pleistocene to discern patterns in avian originations and extinctions during this climatically dynamic period. Geographic Information Systems (GIS) software (Idrisi 1.01, Clark Univ., Worcester, MA) is employed to model sea-level changes in the peninsula during five time periods from 2.5 to 0.01 Ma. Patterns in these originations and extinctions, based on probable habitats occupied by these birds, are inferred from these comparisons to develop a model of avian historical biogeography and community development during the PlioPleistocene. My primary hypothesis here is that, because of its low topography and geography, the Florida peninsula was subject to relatively frequent and rapid changes in land area during the ice ages when even minor sea-level changes (1 m or less) impacted this region. As I will demonstrate below, these changes over the past 2.5 Ma had a significant influence on the composition of avian communities in the peninsula where modem communities developed only recently. This model can be tested and refined with future additions to the fossil record of Florida. The model also may prove beneficial for estimating future changes to avian communities in the Florida peninsula in conjunction with other climate models on this region (e.g., Box et al. 1993).