Table Of ContentPROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
113(1):298-301. 2000.
Fossil Red-shouldered Hawk in the Bahamas: Calohierax quadratus
Wetmore synonymized with Buteo lineatus (Gmelin)
Storrs L. Olson
Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution,
Washington, D.C. 20560, U.S.A.
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A
Abstract. supposedly extinct genus and species of hawk, Calohierax
quadratus Wetmore, was originally described from a fragmentary tarsometa-
tarsus from Quaternary deposits in Little Exuma Island in the Bahamas. This
and a referred tibiotarsus from New Providence, Island, were later assigned to
A
the extant genus Buteo, but their specific identity remained uncertain. pre-
viously unstudied humerus from a cave deposit on New Providence Island,
Bahamas, is here identified with the extant Red-shouldered Hawk, Buteo li-
neatus Gmelin, a species widespread in eastern North America and common
in peninsular Florida but unknown in the Bahamas. The other fossils are as-
signed to this species as well. Calohierax quadratus therefore becomes a syn-
onym of Buteo lineatus, which species has retreated from the Bahamas in the
late Quaternary for reasons that are unclear.
Among the several new species of birds which occurs through most of eastern North
that were described by Wetmore (1937) America and is abundant in Florida, would
from Quaternary cave deposits on Little be considered a more likely candidate for
Exuma Island, Bahamas, was a new genus having occurred in the Bahamas. The Neo-
and species of hawk, Calohierax quadratus, tropical Gray Hawk now occurs only as far
based on the distal end of a tarsometatarsus. north and east as Arizona and Texas. Nev-
The site was not on Great Exuma as Wet- ertheless, there is ample precedent for var-
more originally reported (see Olson and ious Neotropical and western vertebrates
Pregill 1982:3). Brodkorb (1959) later re- having occurred in eastern North America,
ferred the distal end of a tibiotarsus from a particularly Florida, in the Pleistocene (Em-
cave deposit on New Providence Island, slie, 1998), so the possibility of Buteo ni-
Bahamas, to the same species. Restudy of tidus possibly having once occurred in the
these specimens showed that the supposed Bahamas is not unthinkable.
characters of the genus Calohierax were The Bahaman fossil hawk was thus listed
founded entirely on artifacts of wear in the simply as "Buteo sp.", with the genus Ca-
case of the holotype, or intrageneric varia- lohierax Wetmore falling into the synony-
tion in the case of the referred specimen my of Buteo Lacepede, 1799 (Olson & Hil-
&
(Olson Hilgartner 1982). The specimens gartner 1982). The idea that there was an
were otherwise considered to be too frag- extinct hawk in the Bahamas has lingered,
mentary for specific identification, falling however, and Calohierax quadratus has
within the range of size variation of the liv- even appeared, in a reference that I can no
ing Red-shouldered Hawk Buteo lineatus longer recall, under the absurd name
(Gmelin) or Gray Hawk B. nitidus (La- "Quadrate Hawk." Wetmore's specific
tham). name "quadratus", it should be noted, was
Under present geographical and climatic derived from the squared appearance of one
conditions, the Red-shouldered Hawk, of the tarsometatarsal trochleae, a feature
VOLUME 113, NUMBER 299
1
that turned out to be only an artifact ofwear this species "seems to be incompatible
(Olson & Hilgartner 1982). with" the larger Red-tailed Hawk, B. ja-
Because of the ambiguities surrounding maicensis (Gmelin), although this is as
the records of a medium-sized species of much a reflection of the preference of the
Buteo in the Bahamas, it is fortunate that latter for drier uplands rather than being due
an additional specimen bearing on its iden- to competition or antipathy. In any case, it
tity was located in the collections of the is the Red-tailed Hawk that occurs in the
Florida Museum of Natural History. This is Bahamas today, although it is an uncom-
a nearly complete right humerus (UF mon resident only on some of the larger
41801), lacking only a portion of the pec- northern islands and may perhaps be a re-
toral crest. It was collected by J. C. Dick- cent colonist, as it is absent in the fossil
inson and W. Auffenberg in the same "Ba- record.
nana Hole" on New Providence Island that Prior to the arrival of Europeans only a
yielded the fossils that formed the basis of single terrestrial mammal lived in the Ba-
Brodkorb's (1959) study and much of that hamas, the hutia Geocapromys ingrahami
of Olson & Hilgartner (1982). It was col- (Allen), which is now extinct on all but a
lected in 1958-1960, evidently after Brod- single small islet. The adults of this species
korb's study was completed, and since its are too large to have served as prey for
collection has apparently been overlooked. Red-shouldered Hawks, but because these
The fossil humerus is in all details and hawks are very catholic in their choice of
proportions identical with that in Buteo li- food, taking birds, reptiles, amphibians,
neatus (Fig. 1) and in size falls squarely large insects, and even crustaceans in ad-
among males from Florida (Fig. 2), which dition to mammals (Crocoll 1994), and be-
belong to the southeastern subspecies B. I. cause all of these faunal elements are still
alleni Ridgway, which is smaller than the present in the Bahamas, it would be diffi-
nominate subspecies (Crocoll 1994). From cult to correlate the extinction of Buteo li-
the small sample of Buteo nitidus exam- neatus there to lack of suitable prey.
ined, it is clear not only that B. nitidus is a Habitat in most places in the Bahamas is
smaller species, with females in the range not now like that usually considered suit-
of males of B. lineatus in length of the hu- able for Red-shouldered Hawks, but is
merus and the single male being much thought to have been even more xeric in the
& &
smaller (Fig. 2), but the humerus is also past (Pregill Olson 1981, Olson Hil-
much more robust, the shaft especially be- gartner 1982). Thus, environmental and cli-
ing much thicker. Assuming that there was matic changes are also difficult to invoke as
only one species of Buteo in the Bahamas an explanation for the disappearance of this
in this size range, then the holotypical tar- species from the Bahamas in the late Qua-
sometatarsus of Calohierax quadratus from ternary.
Little Exuma would belong to the same spe- The Bahaman fossil records constitute
cies as the humerus from New Providence, the only evidence of Buteo lineatus any-
both islands being on the Great Bahama where in the West Indies, although B. ridg-
Bank. Therefore the species Calohierax wayi of Hispaniola is now usually consid-
quadratus Wetmore, 1937, becomes a ju- ered to be a derivative of B. lineatus (e.g.,
&
nior subjective synonym of Falco lineatus Sibley Monroe 1990), so the Bahamas
Gmelin, 1788. may once have provided a stepping-stone
The Red-shouldered Hawk is normally a for this colonization.
bird of moist riparian woods or swamp-
Acknowledgments
lands, hardly like the dry, scrubby habitats
that predominate in the Bahamas today. I am most grateful to the staffof the Flor-
Brown and Amadon (1968:578) remark that ida Museum of Natural History (UF),
300 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
Fig. 1. Right humeri of Buteo in anconal aspect: A, male Red-shouldered Hawk, B. lineatus, (UF 23893);
B, fossil referred to B. lineatus from New Providence Island, Bahamas (UF 41801); C, female Gray Hawk, B.
nitidus (UF 33746). Scale bar = 2 cm.
17
I I
A A
1 — A A —
16
3 'V* A A
A A A\
"go °
-o 15
*
CO
"A A
14
a>
E H
X
13 I I
70 80 90 100
humerus length
Fig. 2. Scatter diagram showing length of humerus vs. distal width of humerus in male Buteo lineatus
(squares), female B. lineatus (triangles), the Bahaman fossil assigned to B. lineatus (star), female B. nitidus
(circles), and male B. nitidus (X). Five obviously missexed specimens have been corrected. All specimens of
B. lineatus are from Florida and are in the collections of the Florida Museum of Natural History.
VOLUME NUMBER
113, 301
1
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Gainesville, for access to and loan of spec- Florida Peninsula. Ornithological Mono-
Wim.enSstetahdatmamnadaendthTios mstWudeybbpeosrsifbolre:moDdaevrind Olson,gSr.apLh.s, 5&0:1W-.113B.. Hilgartner. 1982. Fossil and
subfossil birds from the Bahamas. Pp. 22-56 in
birds, and Marc Frank for the fossils. The S. L. Ol—son, ed. Fossil vertebrates from the Ba-
photograph is by John Steiner, Smithsonian hamas. Smithsonian Contributions to Paleo-
Photographic Services, and Fig. 2 was pre- biology 48.
&
pared by Helen James. , G. K. Pregill. 1982. Introduction to the pa-
leontology of Bahaman vertebrates. Pp. 1-7 in
S. L. Olson, ed., Fossil vertebrates from the Ba-
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Literature Cited hamas. Smithsonian Contributions to Paleo-
biology 48.
Brodkorb. P. 1959. Pleistocene—birds from New Prov- Pregill. G. K., & S. L. Olson. 1981. Zoogeography of
idence Island, Bahamas. Bulletin of the Flor- West Indian vertebra—tes in relation to Pleisto-
ida State Museum, Biological Sciences 4(11): cene climatic cycles. Annual Review of Ecol-
349-371. ogy and Systematics 12:75-98.
Brown, L., & D. Amadon. 1968. Eagles, hawks, and Sibley, C. G., & B. L. Monroe, Jr. 1990. Distribution
falcons ofthe world. 2 vols. McGraw Hill, New and taxonomy of birds of the world. Yale Uni-
York, 945 pp. versity Press, New Haven, 1111 pp.
Crocoll, S. T.—1994. Red-shouldered Hawk Buteo li- Wetmore, A. 1937. Bird remains from cave de—posits
neatus. Birds of North America 107:1-19. on Great Exuma Island in the Bahamas. Bul-
Emslie, S. D. 1998. Avian community, climate, and letin of the Museum of Comparative Zoology
sea-level changes in the Plio-Pleistocene of the 80:427-441.
