Changes in a West Indian bird community since the late Pleistocene

Abstract

Aim To establish a chronology for late Quaternary avian extinction, extirpation and persistence in the Bahamas, thereby testing the relative roles of climate change and human impact as causes of extinction. Location Great Abaco Island (Abaco), Bahamas, West Indies. Methods We analysed the resident bird community as sampled by Pleistocene (> 11.7 ka) and Holocene (< 11.7 ka) fossils. Each species was classified as extinct (lost globally), extirpated (gone from Abaco but persists elsewhere), or extant (still resident on Abaco). We compared patterns of extinction, extirpation and persistence to independent estimates of climate and sea level for glacial (late Pleistocene) and interglacial (Holocene) times. Results Of 45 bird species identified in Pleistocene fossils, 25 (56%) no longer occur on Abaco (21 extirpated, 4 extinct). Of 37 species recorded in Holocene deposits, 15 (14 extirpated, 1 extinct; total 41%) no longer exist on Abaco. Of the 30 extant species, 12 were recovered as both Pleistocene and Holocene fossils, as were 9 of the 30 extirpated or extinct species. Most of the extinct or extirpated species that were only recorded from Pleistocene contexts are characteristic of open habitats (pine woodlands or grasslands); several of the extirpated species are currently found only where winters are cooler than in the modern or Pleistocene Bahamas. In contrast, most of the extinct or extirpated species recorded from Holocene contexts are habitat generalists. Main conclusions The fossil evidence suggests two main times of late Quaternary avian extirpation and extinction in the Bahamas. The first was during the PleistoceneHolocene transition (PHT; 15-9 ka) and was fuelled by climate change and associated changes in sea level and island area. The second took place during the late Holocene (< 4 ka, perhaps primarily < 1 ka) and can be attributed to human impact. Although some species lost during the PHT are currently found where climates are cooler and drier than in the Bahamas today, a taxonomically and ecologically diverse set of species persisted through that major climate change but did not survive the past millennium of human presence.

Vertebrate community on an ice-age Caribbean island

“…Four of these species (all but P. fulva) currently occupy climates that are cooler and in some cases drier than the modern Bahamas (38). The two swallows are cliff nesters; the other three species are characteristic of grassland or pine woodland.…”

“…Climate models have the West Indies being cooler and drier in the late Pleistocene than today (44,45). By analogy with the habitat preferences of extant conspecific or congeneric taxa, the bird evidence suggests that pine woodlands or pine grasslands (savannas) dominated the large island formed by the Little Bahama Bank during the late Pleistocene (38).…”

Regional variation in Caribbean dry forest tree species composition

“…Upland habitats on Eleuthera are dominated by broadleaf dry forest and scrub. Abaco and Eleuthera, lying on different Bahamian Banks, would have each been part of much larger islands and closer together when these shallow banks were exposed at lower sea-levels during much of the Pleistocene (Steadman and Franklin 2015).…”

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

“…Dispersal among these geologically distinctive places, as well as among the low, geologically uniform islands sitting atop the carbonate banks of the Bahamas, involved shorter distances during glacial than interglacial times but still required the birds to fly over the ocean (ref. 6, tables S2 and S3 therein).…”

“…While this statement holds true on West Indian islands as much as on any other set of islands (2)(3)(4), an ice age (Pleistocene glacial interval; >9 ka, but not precisely dated) vertebrate fauna from Sawmill Sink, a blue hole on Abaco Island in the northern Bahamas, featured 17 resident species of birds known from Abaco only as Pleistocene fossils (5). None of these 17 species have been recorded in Abaco's record of Holocene bird fossils, dated to ≤5 ka (3,6). This paper will focus on two of the Pleistocene bird populations that likely were lost to changes in climate and sea level that took place during the Pleistocene-Holocene transition (PHT) from ∼15 to 9 ka, well before any human presence in the Bahamas.…”