The pasturelands interspersed with woodlots that cover much of rural south Florida today likely resemble the coastal oak and pine savannahs of this same region during the Pleistocene. South Florida and the southern Gulf Coast were climatically out of sync with the rest of North America during Ice Ages. When climate phases of dry cold conditions struck the rest of North America, south Florida and the southern Gulf Coast experienced warmer wetter subtropical climates. The Gulf Stream of the present day carries tropically heated water north, keeping climates in the northern latitudes of North America relatively moderate, but during cold climate phases of the Ice Age, it shut down. Instead, this warm water stayed at lower latitudes ironically making climate along the southern Gulf Coast even warmer than present day conditions. This warm climate spurred frequent thunderstorms and hurricanes. Lightning-ignited fires and windstorms destroyed trees and created open savannahs where mammoths, bison, and horses further suppressed the growth of unbroken forests. Trees that survived fire and wind were spaced far apart, and woodlots were restricted to the vicinity of waterholes where the trees were protected by watery fire breaks. This warm savannah habitat occurred from south Florida, Alabama, Mississippi, Louisiana, and Texas all the way to eastern Mexico. Much of this land has been inundated by sea level rise since the end of the last Ice Age. Warm coastal savannahs were ideal habitat for many species of plants and animals including caracaras.
Two species of caracaras inhabited Gulf Coast savannahs during the last Ice age–the crested caracara (Polyborus plancus) and the yellow-headed caracara (Milvago reidei). The former still occurs as a relict population in south Florida. This species lived on dry prairies throughout much of Florida, but that type of habitat has largely been transformed to rural, suburban, and urban landscapes. A recent scientific study in Florida found 103 crested caracara nests, and most of those were on improved pastureland. They seem to prefer pastureland over what remains of their original dry prairie habitat. I think this is a clue they benefit from the presence of megafauna. During the present day this means herds of cattle, but formerly they accompanied now extinct and extirpated megafauna. Caracaras forage on the ground for carrion. There was an abundance of carrion during the Pleistocene. They hunt for insects, reptiles, and small mammals stirred up by grazing herds of megafauna. And along with swallow-tailed kites and other opportunistic birds, they hunt down small animals fleeing wildfires. The widely spaced trees and small woodlots located on the pastures or savannahs are used for nesting.
Fossil remains of both species were found at the Cutler Hammock site located in Miami, Florida. Yellow-headed caracaras no longer occur in North America, but habitat during some phases of Ice Age climate was so favorable in this region that it attracted both species. The Cutler Hammock site is notable for having yielded many remains of large carnivores including dire wolf, saber-tooth, giant lion, jaguar, and cougar. Their kills helped feed a diverse population of avian scavengers.
Reference:
Morrison Joan
“The Crested Caracara in the Changing Grasslands of Florida”
Click to access 3-17145_p.21115_Mor_FDPC_d.pdf
Tags: crested caracara, Pleistocene south Gulf Coast climate out of sync, yellow-headed caracara
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