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Old Monday 28th August 2017, 23:16   #1
Fred Ruhe
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bluebirds and crossbills in the Bahamas

David W. Steadman & Janet Franklin, 2017

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

Proceedings of the National Academy of Sciences of the United States of America in press

Significance

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 Sialia sialis and Hispaniolan crossbill Loxia megaplaga) 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.

Abstract: http://www.pnas.org/content/early/20...60114.abstract

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 (Sialia sialis) and Hispaniolan crossbill (Loxia megaplaga). Each species lives today only outside of the Bahamian Archipelago, with S. sialis occurring in North and Central America and L. megaplaga 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.

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Old Friday 10th November 2017, 23:24   #2
Fred Ruhe
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Craig W. Benkman, 2017

Crossbills were unlikely resident in the Bahamas; thus, there was no population to be extirpated

doi: 10.1073/pnas.1716928114

Abstract:

In PNAS, Steadman and Franklin (1) make the argument that the large reduction in land area and shift in vegetation in the Bahamian Archipelago from ∼15–9 ka caused declines and extirpation of two bird species, the Eastern bluebird (Sialia sialis) and Hispaniolan crossbill (Loxia megaplaga). Their evidence for L. megaplaga resides in fossil bones from the Bahamian island of Abaco, representing eight individuals from >9 ka. Two of three qualitative traits from the only mandible recovered provided a better match for L. megaplaga than for red crossbills (Loxia curvirostra) from North America. However, their measurements of the postcranial bones for their other specimens do not allow one to eliminate the possibility that they represent L. curvirostra

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Old Friday 10th November 2017, 23:31   #3
Fred Ruhe
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David W. Steadmana and Janet Franklin, 2017

Reply to Benkman: Hispaniolan crossbills formerly resided in the Bahamas

David W. Steadman, doi: 10.1073/pnas.1717497114

We appreciate the issues raised in Benkman’s letter (1), which is critical of our paper (2). Here, we will address these issues.

Benkman (1) believes that the late Pleistocene Bahamian (Abaco island) fossils we identified as Hispaniolan crossbill (Loxia megaplaga), in fact, represent nonresident individuals of red crossbill (Loxia curvirostra). The title of his letter begins with “Crossbills were unlikely resident in the Bahamas” (leaving some uncertainty), but concludes with apparent certainty that “thus, there was no population to …

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