Journal of Biogeography
SUPPORTING INFORMATION
Changes in an insular bird community since the late Pleistocene
David W. Steadman and Janet Franklin
APPENDIX S1 Detailed descriptions of fossil sites and excavation methods.
Descriptions of fossil sites
Sawmill Sink (26.21767° N, 77.21052° W, WGS84 datum) is an inland blue hole that
contains tidally influenced water of fresh, marine and mixed chemistry. The nearly
circular opening of Sawmill Sink has a diameter ≤ 15.5 m. Dissolutional undercutting
and subsequent collapse of the carbonate rock has created a bell-shaped profile that
encircles a well-developed talus cone from a depth of 9–34 m (Steadman et al., 2007):
Fig. 2). Much of the talus cone is covered with peat rich in plant micro- and macrofossils
and Holocene vertebrate fossils that have been collected by scuba divers since 2004.
Fossils associated with this peat deposit are Holocene in age, based on numerous radiocarbon dates on non-bird fossils (Steadman et al., 2007; Hastings et al., 2014) as well as
bird fossils (reported herein). The stratified water profile at Sawmill Sink consists of
fresh water (surface to 9.5 m depth), a halocline with mixed water chemistry (9.5–17 m
depth) where hydrogen sulfide and sulfur-reducing bacteria block all penetrating light,
and, below 17 m depth, tidally-influenced, anoxic salt water (Gonzalez et al., 2011).
Fossils in inorganic sediments on bedrock ledges at depths of 27–34 m are considered
to be late Pleistocene in age because they represent prey remains from owl roosts that
were active when sea level was at least 35 m lower than at present. Such a sea level
occurred only at ages > 11 ka (Bard et al., 2010). None of the fossils from these owl
roosts that we have tried to radiocarbon date have yielded enough collagen to do so.
Ralph’s Cave (26.24997° N, 77.19004° W) is a blue hole, the entrance to which
lies c. 4 km north of Sawmill Sink. Vertebrate fossils have been collected from organic
sediments in fresh water at shallow depths (< 5 m) at Ralph’s Cave since 2010. Access to
this site is through a 6-m diameter collapse in a thin limestone roof, leading to a waterfilled chamber (c. 15 m × 9 m) only 3 m below. All radiocarbon determinations from
Ralph’s Cave (six dates on bat fossils) are late Holocene in age (D.W. Steadman, unpublished data).
Hole-in-the-Wall Cave (25.86021° N, 77.18369° W) is developed near the southern tip of Abaco. This complex cave, with a total length of 1207 m (Walker et al., 2008),
yielded fossils from dry, unstratified, inorganic sediments excavated by N. A. Albury and
G. S. Morgan in January 1989. Bird fossils from the two excavations (south entrance and
north entrance) are similar in preservation and species composition. This site was undated until the age determinations reported here.
The Gilpin Point site (26.10457° N, 77.17767° W) is a peat deposit lying in an
area of irregular limestone outcrops and calcareous beach sand on the windward
(Atlantic Ocean) coast of southern Abaco. Discovered in 2009, the dark, peaty sediment
Journal of Biogeography
Supporting Information
at Gilpin Point is inundated today by the ocean under normal circumstances, as well as
covered by calcareous sand in the summer months (Steadman et al., 2014). Access to
the sediment is typically only possible during very low (spring) tides associated with
certain new and full moons in the autumn, winter and spring. The peat can be exposed
and then completely covered by sand over a single tidal cycle. Wood, snails and bones
occur throughout the vertical sequence of the peaty sediment at Gilpin Point, which is
late Holocene in age based on a variety of dated materials (Steadman et al., 2014).
Field data collection
Underwater palaeontological operations in blue holes use industry-standard cave-diving
techniques and scientific diving protocols (details in Steadman et al., 2007). All fossils and
associated sediments collected at Sawmill Sink and Ralph’s Cave have both vertical (water
depth) and horizontal (N–S, E–W grid) coordinates. The samples were sealed in Ziploc
bags and plastic boxes to secure them within their original water chemistry (anoxic salt
water for Sawmill Sink, fresh water for Ralph’s Cave) during transport to the laboratory.
Preparation in the lab consisted of a series of increasingly fresh water washes to remove
salts, followed by gradual air-drying. Fossils from dry caves (Hole-in-the Wall Cave and
Banana Hole) were excavated with minimal vertical and horizontal control within the
unstratified sediment, and retrieved by both dry-screening and water-screening through
nested sieves of 12.5, 6.4, 3.2 and 1.6-mm mesh (Olson & Pregill, 1982). Fossils from the
intertidal peat deposit at Gilpin Point were retrieved from 1.5–6 L blocks of sediment
excavated with a square shovel and water-screened either in the field (nested sieves of
12.5, 6.4 and 1.6-mm mesh) or in the lab (nested sieves of 12.5, 5.6, 3.35, 2.0 and 1.0-mm
mesh; details in Steadman et al., 2014).
Certain very delicate avian fossils were consolidated by applying Butvar (polyvinyl
acetate); no fossils treated with Butvar were radiocarbon-dated. No chemicals were
applied to any other fossils except for specimens lightly encrusted with calcium carbonate, which was etched away through soaking for 30–90 min in dilute (3–5%) acetic acid.
REFERENCES
Bard, E., Hamelin, B. & Delanghe-Sabatier, D. (2010) Deglacial meltwater pulse 1B and Younger Dryas sea
levels revisited with boreholes at Tahiti. Science, 327, 1235–1237.
Gonzalez, B.C., Iliffe, T.M., Macalady, J.L., Schaperdoth, I. & Kakuk, B. (2011) Microbial hotspots in
anchialine blue holes: initial discoveries from the Bahamas. Hydrobiologia, 677, 149–156.
Hastings, A.K., Krigbaum, J., Steadman, D.W. & Albury, N.A. (2014) Domination by reptiles in a terrestrial
food web of The Bahamas prior to human occupation. Journal of Herpetology, 48, 380-388.
Olson, S.L. & Pregill, G.K. (1982) Introduction to the paleontology of Bahaman vertebrates. Smithsonian
Contributions to Paleobiology, 48, 1–7.
Steadman, D.W., Albury, N.A., Maillis, P., Mead, J.I., Slapcinsky, J.D., Krysko, K.L., Singleton, H.M. & Franklin,
J. (2014) Late-Holocene faunal and landscape change in the Bahamas. The Holocene, 24, 220–223.
Steadman, D.W., Franz, R., Morgan, G.S., Albury, N.A., Kakuk, B., Broad, K., Franz, S.E., Tinker, K., Pateman,
M.P., Lott, T.A., Jarzen, D.M. & Dilcher, D.L. (2007) Exceptionally well preserved late Quaternary plant
and vertebrate fossils from a blue hole on Abaco, The Bahamas. Proceedings of the National Academy of
Sciences USA, 104, 19897–19902.
Walker, L.N., Mylroie, J.E., Walker, A.D. & Mylroie, J.R. (2008) The caves of Abaco Islands, Bahamas: keys to
geologic timelines. Journal of Cave and Karst Studies, 70, 108–119.
D. W. Steadman & J. Franklin
Pleistocene–Holocene changes in an insular bird community
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Journal of Biogeography
Supporting Information
APPENDIX S2 Island areas and interisland distances estimated for sea levels from the
Last Glacial Maximum to early Holocene.
Island areas for the Bahamian Archipelago and Greater Antilles (Table S1), and interisland distances from the Little (Table S2) and Great Bahamas Banks (Table S3) were
estimated for early Holocene (c. 12–11 ka) and Last Glacial Maximum (c. 23–19 ka) sea
levels. We used a global topographic database that includes seafloor topography (Smith
& Sandwell, 1997) and well-accepted references for late Quaternary sea levels (Clark &
Mix, 2000; Bard et al., 2010) to estimate the land areas of Bahamian islands and their
interisland distances during and since the LGM (23–19 ka). Global topographic data
were available at 1-minute (roughly 2 km) resolution from http://topex.ucsd.edu/cgibin/get_data.cgi (accessed 1 Jun 2012). These point data were interpolated to a raster
grid by kriging, and then reclassified for each of the target sea levels. A sea level of -40 m
was used to represent 12–11 ka; we also calculated land areas and interisland distances
for sea levels of −35 and −45 m to account for uncertainty in sea-level curves and topographic data. A −120-m sea level is estimated for the LGM (Yokoyama et al., 2000), with
uncertainty characterized using −105 and −135 m. Areas and distances were calculated
by projecting each new shoreline map (WGS 1984 UTM Zone 17N), and then measuring
the shortest distance between islands. Analyses were carried out using ARCMAP 9.3
(ESRI, Redlands, CA). Current land areas of islands are from the United Nations Island
Directory (http://islands.unep.ch/isldir.htm; accessed 24 Jun 2012).
REFERENCES
Bard, E., Hamelin, B. & Delanghe-Sabatier, D. (2010) Deglacial meltwater pulse 1B and Younger Dryas sea
levels revisited with boreholes at Tahiti. Science, 327, 1235–1237.
Clark, P.U. & Mix, A.C. (2000) Ice sheets by volume. Nature, 406, 689–690.
Smith, W.H.F. & Sandwell, D.T. (1997) Global sea floor topography from satellite altimetry and ship depth
soundings. Science, 277, 1956–1962.
Yokoyama, Y., Lambeck, K., De Deckker, P., Johnston, P. & Fifield, L.K. (2000) Timing of the Last Glacial
Maximum from observed sea-level minima. Nature, 406, 713–716.
D. W. Steadman & J. Franklin
Pleistocene–Holocene changes in an insular bird community
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Journal of Biogeography
Supporting Information
Table S1 Current and estimated island area (km2) at sea levels corresponding to c. 12–
11 ka (−40 m, with −35 m and −45 m representing uncertainty), and c. 23–19 ka
(−120 m, with −105 m and −135 m). Areas under lower sea levels estimated from global
topographic data available in 1-minute (roughly 2 km) resolution from http://topex
.ucsd.edu/cgi-bin/get_data.cgi (accessed 1 June 2012). Current areas are from the
United Nations Island Directory (http://islands.unep.ch/isldir.htm; accessed 24 June
2012).
Sea level
Island group
Current
Little Bahama Bank
1224 (Ab)
1096 (GB)
4887 (An)
6754 (Ot)
770
Great Bahama Bank
Turks and Caicos
Cuba
Hispaniola
Puerto Rico
Jamaica
105,805
73,929
9100
11,190
−35 m
−40 m
−45 m
−105 m
−120 m
−135 m
13,880
14,254
14,550
16,492
16,748
17,004
92,297
93,359
94,279
102,231
103,030
103,670
1385 (Nc)
1077 (Sc)
384 (T)
162,340
83,550
16,532
13,796
2552 (C)
2647(C)
3547 (C)
3855 (C)
4192 (C)
393 (T)
162,794
84,065
17,221
13,894
406 (T)
163,234
84,624
17,749
13,992
507 (T)
165,887
87,587
20,099
14,771
510 (T)
166,294
88,094
20,218
14,970
525 (T)
166,674
88,645
20,322
15,136
Ab, Abaco; GB, Grand Bahama; An, Andros; Ot, other islands of the Great Bahama Bank (New Providence,
Eleuthera, Exumas, Cat and Long); Nc, North Caicos island at lower sea level; Sc, South Caicos island at
lower sea level; C, Caicos Bank; T, Turks Bank.
D. W. Steadman & J. Franklin
Pleistocene–Holocene changes in an insular bird community
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Journal of Biogeography
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Table S2 Distances (km) from Abaco to other islands in the Bahamas, Greater Antilles
and Florida, USA, at current sea level, and distances from the Little Bahama Bank
superisland to other expanded islands at sea levels of −40 m (corresponding to c. 12–
11 ka) and −120 m (c. 23–19 ka). Distances under lower sea levels were estimated from
global topographic data available at 1-minute (roughly 2 km) resolution from
http://topex.ucsd.edu/cgi-bin/get_data.cgi (accessed 1 June 2012).
Modern island
Cuba
Hispaniola
Jamaica
Puerto Rico
Mainland Florida
Grand Bahama
Eleuthera
New Providence
Andros, North
Andros, South
Cat
Great Exuma
Long
Crooked
Acklins
Rum Cay
San Salvador
Great Inagua
Little Inagua
Mayaguana
East / Middle Caicos
North Caicos
Providenciales
Grand Turk
Current
distance to
Abaco (km)
412
772
811
1329
221
25
45
81
109
179
193
265
299
443
480
330
330
638
640
558
699
680
667
739
D. W. Steadman & J. Franklin
Distance to Little Bahama Bank
Glacial (super-)
island
At −40 m sea level
At −120 m sea level
Cuba
Hispaniola
Jamaica
Puerto Rico
Mainland Florida
Little Bahama Bank
Great Bahama Bank
384
770
810
1324
87
—
34
381
764
806
1312
76
—
34
Crooked / Acklins
435
428
Rum Cay
San Salvador
Inagua
328
327
635
316
321
629
Mayaguana
Caicos Bank
555
660
548
654
Turks Bank
700
694
Pleistocene–Holocene changes in an insular bird community
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Journal of Biogeography
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Table S3 Distances (km) from South Andros to other islands in the Bahamas, Greater
Antilles and Florida, USA, at current sea level, and distances from the Great Bahama
Bank superisland to other expanded islands at sea level −40 m (corresponding to c. 12–
11 ka) and −120 m (c. 23–19 ka). Distances under lower sea levels estimated from
global topographic data available in 1-minute (roughly 2 km) resolution from
http://topex.ucsd.edu/cgi-bin/get_data.cgi (accessed 1 June 2012).
Modern island
Cuba
Hispaniola
Jamaica
Puerto Rico
Mainland Florida
Abaco
Grand Bahama
Eleuthera
New Providence
Andros, North
Cat
Great Exuma
Long
Crooked
Acklins
Rum Cay
San Salvador
Great Inagua
Little Inagua
Mayaguana
East / Middle Caicos
North Caicos
Providenciales
Grand Turk
Distance to
South Andros
(km)
177
609
571
1233
276
179
249
141
78
14
185
138
217
343
376
262
299
494
524
473
616
598
576
656
D. W. Steadman & J. Franklin
Distance to Great Bahama Bank
Glacial (super-)
island
At −40 m sea level
At −120 m sea level
Cuba
Hispaniola
Jamaica
Puerto Rico
Mainland Florida
Little Bahama Bank
22
304
385
930
77
34
20
301
386
926
74
34
Great Bahamas
Bank
—
—
Crooked / Acklins
45
43
Rum Cay
San Salvador
Inagua
25
75
186
23
68
184
Mayaguana
Caicos Bank
178
275
176
273
Turks Bank
315
313
Pleistocene–Holocene changes in an insular bird community
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Journal of Biogeography
Supporting Information
APPENDIX S3 Climate scatter-plots showing annual mean precipitation versus average
minimum temperature of the coldest month for the six species identified on Great Abaco
Island from Pleistocene but not Holocene deposits and that no longer occur in the
Bahamas, and for modern and Last Glacial Maximum (LGM) Bahamas climates
estimated from the Community Climate System Model (CCSM) and the Model for
Interdisciplinary Research on Climate (MIROC).
2000
3000
20
10
0
-10
-20
0
1000
2000
3000
2000
3000
10
0
-10
-20
Bird points
Bahamas modern
LGM CCSM
LGM MIROC
-30
10
0
-10
-20
1000
4000
0
1000
2000
3000
Cave swallow
2000
3000
D. W. Steadman & J. Franklin
4000
10
0
-10
-20
Bird points
Bahamas modern
LGM CCSM
LGM MIROC
-30
10
0
-10
-20
-30
1000
4000
20
Short-eared owl
Minimum temperature ( ° C)
Annual precipitation (mm)
20
Annual precipitation (mm)
Annual precipitation (mm)
4000
20
Eastern meadowlark
Minimum temperature ( ° C)
Cliff swallow
20
Annual precipitation (mm)
Bird points
Bahamas modern
LGM CCSM
LGM MIROC
0
-30
4000
Bird points
Bahamas modern
LGM CCSM
LGM MIROC
0
Minimum temperature ( ° C)
20
10
0
-10
-20
1000
Bird points
Bahamas modern
LGM CCSM
LGM MIROC
Annual precipitation (mm)
-30
Minimum temperature ( ° C)
0
Minimum temperature ( ° C)
Eastern bluebird
Bird points
Bahamas modern
LGM CCSM
LGM MIROC
-30
Minimum temperature ( ° C)
Brown-headed nuthatch
0
1000
2000
3000
4000
Annual precipitation (mm)
Pleistocene–Holocene changes in an insular bird community
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