Origin, paleoecology, and extirpation of bluebirds and crossbills in the Bahamas across the last glacial–interglacial transition

Abstract

<p id="d15026298e162">On tropical islands, extensive extirpation of birds and other vertebrates occurred during the Holocene, following human arrival. Much less is known about pre-Holocene extirpation on islands. We focus on two species (Eastern bluebird <i>Sialia sialis</i> and Hispaniolan crossbill <i>Loxia megaplaga</i>) that were lost in the Bahamas to changes in sea level (becoming higher), land area (getting smaller), climate (becoming warmer and wetter), and habitat (loss of pine grassland) that took place during the last glacial–interglacial transition, many millennia before peopling of the islands. While volant, the bluebird evolved a short wing in the Bahamas, whereas the crossbill retained a similar morphology to the surviving population on Hispaniola. Each major glacial–interglacial shift reconfigured the resident Bahamian flora and fauna. </p><p class="first" id="d15026298e171">On low islands or island groups such as the Bahamas, surrounded by shallow oceans, Quaternary glacial–interglacial changes in climate and sea level had major effects on terrestrial plant and animal communities. We examine the paleoecology of two species of songbirds (Passeriformes) recorded as Late Pleistocene fossils on the Bahamian island of Abaco—the Eastern bluebird ( <i>Sialia siali</i>s) and Hispaniolan crossbill ( <i>Loxia megaplaga</i>). Each species lives today only outside of the Bahamian Archipelago, with <i>S. sialis</i> occurring in North and Central America and <i>L. megaplaga</i> endemic to Hispaniola. Unrecorded in the Holocene fossil record of Abaco, both of these species probably colonized Abaco during the last glacial interval but were eliminated when the island became much smaller, warmer, wetter, and more isolated during the last glacial–interglacial transition from ∼15 to 9 ka. Today’s warming temperatures and rising sea levels, although not as great in magnitude as those that took place from ∼15 to 9 ka, are occurring rapidly and may contribute to considerable biotic change on islands by acting in synergy with direct human impacts. </p>