Flooded Bat Caves of the Caribbean

Sea level rise following the end of the most recent Ice Age reduced the land area of the Caribbean Islands.  (See: https://markgelbart.wordpress.com/2011/11/11/banana-hole-fossil-sites/ )  The Bahamas, now consisting of numerous small islands, was formerly 1 big island.  During the Pleistocene the Caribbean Islands hosted an interesting, if depauperate, mammalian fauna including dwarf ground sloths, monkeys, rodents, insectivores, and bats.  The extinctions of dwarf ground sloths on Caribbean Islands occurred well after the extinctions of mainland ground sloths, and the timing is associated with the colonization of the islands by people. However, a recent study of bat extinctions and extirpations on Caribbean Islands suggested they were caused by rising sea levels that flooded cave roosts and reduced the area of suitable bat habitat.  But there was a big flaw in this study–the authors didn’t use radiocarbon dating of subfossil bat material.  A newer study remedied this flaw and determined Caribbean bat extirpations occurred thousands of years after sea level rose near present day levels.  The authors of this study focused on specimens of the 9 species of bats found in Ralph’s Cave on Abaco, the northernmost island of the Bahamas.

Location of Abaco, northernmost island of the Bahamas.  There are partially flooded caves underneath the surface of this island that serve as bat roosts.

Ralph's Cave, Abaco (Brian Kakuk) 15.5 : 4

Ralph’s Cave. Bats roost in the parts that are above water.

Of the 97 bat bones found in Ralph’s Cave, 51 of the specimens belong to species that still roost in the cavern, parts of which are still above water.  The extant species include the big brown bat (Eptesicus fucus), Bahamian funnel-eared bat (Chilonotulus tinisterferons), buffy flower bat (Erophylla segherum), and Waterhouse’s leaf-nosed bat (Macrotus waterhousii).  The bones of 5 species of bats that no longer inhabit Abaco were excavated from the cave as well.  These include specimens of the Greater Antillean long-tongued bat (Monophyllus redmani), Parnell’s mustache bat (Pteronotus parnelli), Cuban greater funnel-eared bat (Natalus primos), minor red bat (Lasiurus minor), and the southeastern myotis (Myotis austroriparius).  Radiocarbon dates of the minor red bat, Cuban greater funnel-eared bat, and Parnell’s mustache bat show these 3 species lived on Abaco as recently as 3600 BP.  The southeastern myotis, a widespread bat in southeastern North America, still inhabited Abaco 4000 years ago, and the Greater Antillean long-tongued bat occurred on the island until 1700 BP.  Radiocarbon dating of additional specimens of these locally extirpated bats may show they lived on Abaco even more recently.

Picture

The Greater Antillan Long-tongued bat eats nectar, fruit, and insects.  They’ve been extirpated from Abaco.

Pteronotus parnellii

Parnell’s mustache bat.  Also extirpated from Abaco.

The Cuban greater funnel-eared bat is extirpated from the Bahamas and is in danger of extinction in its last stronghold–Cuba.  The 1 cave where it still roosts recently collapsed.

The authors of this study also calculated the amount of suitable bat habitat on Abaco, and they determined “the minimum amount of bat habitat to sustain viable bat populations (of the extirpated species) was unchanged” following the transition from the Pleistocene to the Holocene.  Bat habitat shrank but not enough to cause these species to disappear.  The authors of this paper stated “the precise mechanism (of extirpation) is undetermined.”  They suggest human activities may have played a role.  Humans setting fires, clearing forests, or directly gathering the bats could have been detrimental to the extirpated species.  I don’t think humans preyed on these bats because they are too small.  Humans do eat flying foxes in Asia, but these fruit-eating bats are sizable and have substantial meat on their bones.  If humans are responsible for the extirpation of some bat species on Abaco, it must be through some form of habitat alteration.

References:

Centene, J. Angel; and David Steadman

“Fossils Reject Climate Change as the Cause of Extinctions of Caribbean Bats”

Scientific Reports 2015

Danalos, Lilliana; and Amy Russell

“Deglaciation Explains Bat Extinctions in the Caribbean”

Ecology and Evolution November 2012

 

 

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