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Discovery of the Imperiled Miami Blue Butterfly (Cyclargus
thomasi bethunebakeri) on Islands in the Florida Keys National
Wildlife Refuges, Monroe County
Paula Cannon1, Tom Wilmers2,* and Katie Lyons3
Abstract - A once common butterfly found only in Florida, Cyclargus thomasi bethunebakeri
(Miami Blue), declined to near extinction during the 1990s. On 26 November 2006, we discovered
this species on Boca Grande Key, 76 km west of Bahia Honda Key. Previously, the
butterfly was only known to survive on Bahia Honda Key. Over the following 8-month period,
we searched periodically for this butterfly on islands in the Great White Heron National Wildlife
Refuge (GWHWNR) and the Key West National Wildlife Refuge (KWNWR). The Miami
Blue was not found on 6 islands in GWHNWR, but was present at 8 of 10 areas in KWNWR.
Seven of the occupied sites were on islands in the Marquesas Keys. The number of Miami Blue
adults varied greatly by island and season, but were highest at the two largest colonies when
Pithecellobium keyense (Blackbead; both a larval host and adult nectar plant) was flowering and
producing new leaves. Eight other plant species were visited by adult Miami Blues for nectar.
Threats to the newly discovered colonies are discussed.
Cyclargus thomasi bethunebakeri Comstock and Huntington (Miami Blue) was
once widely distributed in coastal areas of southern and central Florida (Calhoun et al.
2002, Minno and Emmel 1994). The butterfly declined and disappeared from much of
its former range by the 1980s, but still survived in the Florida Keys (Leston et al. 1982).
In the years following Hurricane Andrew in 1992, the Miami Blue seemed to disappear
from the Keys as well (Calhoun et al. 2002). Then in 1999, the Miami Blue was discovered
at Bahia Honda State Park in the lower Keys (Ruffin and Glassberg 2000).
Here we report on the discovery of additional Miami Blue colonies on islands in
the Key West National Wildlife Refuge, west of Key West. We also present notes on
the abundance, biology, and threats to this imperiled butterfly.
Study Area and Methods. Our work was performed on uninhabited islands in the
Key West National Wildlife Refuge (KWNWR) and the Great White Heron National
Wildlife Refuge (GWHNWR). These refuges are situated in the lower Florida Keys
where the climate is subtropical. Islands in the study area are nearly flat. Most are
less than 1 m above sea level, with none >2 m in elevation.
We searched for adult Miami Blues in 16 areas (1 to 9 visits per area), 6 in the
GHWNR and 10 in the KWNWR (Table 1). Of the latter, 7 were in the Marquesas
Keys, a circular array of islands 29 to 37 km west of Key West, fl. The largest island
in the Marquesas Keys contains 3 upland tracts, separated from each other by
500–3500 m of mangrove forest. Because unsuitable habitat only 30 m wide may
curtail Miami Blue dispersal (Saarinen and Daniels 2005), we considered each of
these 3 uplands separate study sites called Long Beach, Snook Beach, and East Cove.
All other sites in the study area were on individual islands.
Twelve of the 16 study sites had narrow coastal strands and dunes fronted by
beaches (range = 50–2900 m long) (Table 1). Two sites contained only a hardwood
hammock, and two others consisted of upland coastal strands fronted by mangroves
(Table 1). The size of the upland areas differed greatly among islands, ranging from
less than 0.1 ha to ≈15 ha.
Notes of the Southeastern Nat u ral ist, Issue 9/4, 2010
12661 Central Avenue, Big Pine Key, fl33043. 2Florida Keys National Wildlife Refuges, Big
Pine Key, fl33043. 38204 County Road 3140 Mountain View, MO 65548. *Corresponding
author - firstname.lastname@example.org.
848 Southeastern Naturalist Notes Vol. 9, No. 4
We used checklist counting, a method that is more efficient than transects for
initially determining species presence (Royer et al. 1998), to document the distribution
and abundance of Miami Blues. With checklist counting, an unrestricted search
of potentially suitable habitat is made, and target species are counted without regard
to other factors (Royer et al. 1998). We recorded the number of adult Miami Blues
observed at each site and the time spent searching.
We also made systematic counts of adult Miami Blues over the entire upland
areas of Boca Grande Key on 3 February, 9 April, and 23 July and at Main Beach in
the Marquesas Keys on 8 January and 10 March 2007. For the systematic counts, we
divided the uplands into 3 parallel transects (each >350 m) so that each of us could
cover a different area simultaneously to reduce the possibility of double counting.
We walked very slowly along the transects and used binoculars that focused to <2 m
to view and positively identify the butterflies. Each observer used a digital counter
to tally the number of adults seen. The duration of the systematic counts ranged from
3.1 to 4.5 hours.
In KWNWR, but not GWHNWR, dense patches of dead trees and shrubs blown
down by Hurricane Wilma were intermixed with live vegetation, precluding a search
of parts of the uplands.
On all islands, we searched for the butterfly’s known host plants (Minno and
Emmel 1993, Minno et al. 2005) and incidentally documented their use by the Miami
Blue. We also recorded incidental observations of plants visited for nectar by
Observations and Discussion. In the KWNWR, Miami Blues were found on Boca
Grande Key and five islands in the Marquesas Keys, including three different sites
on one island (Tables 1, 2). Upland areas (i.e., dune/coastal strand) occupied by the
Miami Blue ranged from ≈0.1–15 ha (Table 1). All areas harboring this butterfly contained
Pithecellobium keyense Britton (Blackbead), the observed larval host plant.
Table 1. Characteristics of areas surveyed for Miami Blues (MB) in the Florida Keys National
Wildlife Refuges; H = hardwood hammock only; BDC = dune and coastal strand fronted by
beach, NB = coastal strand landward of a mangrove fringe, N/A = no beach or dune.
Area MB present Upland size (ha) Upland type Beach length (m)
Great White Heron NWR:
Johnson Key No 0.3 H N/A
Johnston Key No 0.1 H N/A
Porpoise Key No 0.1 NB N/A
Sawyer Keys (NE) No 0.5 NB N/A
Sawyer Keys (NW) No 2.0 BDC 100
Snipe Point No 2.0 BDC 125
Key West NWR:
Boca Grande Key Yes 4.0 BDC 1220
Man Key (east) No 1.0 BDC 50
Island 1 (East Cove) Yes 0.1 BDC 215
Island 1 (Long Beach) Yes 15.0 BDC 2900
Island 1 (Snook Beach) Yes 1.0 BDC 525
Island 2 (Main Beach) Yes 2.0 BDC 1065
Island 3 (New Beach) Yes 0.2 BDC 85
Island 4 (Short Beach) Yes 0.5 BDC 450
Island 5 (Third Beach) Yes 1.0 BDC 500
Woman Key No 3.0 BDC 1300
2010 Southeastern Naturalist Notes 849
We made our first discovery of Miami Blues on 26 November 2006 at Boca
Grande Key (9 adults), located 19 km west of Key West and about 76 km west of
the known colony on Bahia Honda Key. Several Miami Blues were photographed,
including a female laying eggs on Blackbead (Fig. 1) . The occupied habitat consisted
Figure 1. A female Miami Blue ovipositing on a Blackbead flower bud on Boca Grande Key,
26 November 2006 (A); female Miami Blue nectaring on a Blackbead flower on Marquesas
Keys, 3 December 2006 (B); egg found on Blackbead flower buds on Boca Grande Key, 26
November 2006 (C).
Table 2. Number of adult Miami Blues (MB) observed in the Key West National Wildlife Refuge,
November 2006–July 2007. Bold text indicates replicate transects. All others are checklist
counts in selected uplands. Asterisk denotes MB presence but no count taken.
Island Date No. MB
Boca Grande 11/26/2006 9
Boca Grande 1/23/2007 100
Boca Grande 2/3/2007 441
Boca Grande 4/9/2007 51
Boca Grande 4/20/2007 30
Boca Grande 5/28/2007 0
Boca Grande 6/18/2007 1
Boca Grande 7/16/2007 *
Boca Grande 7/23/2007 89
East Cove 1/23/2007 12
Long Beach 12/3/2006 7
Long Beach 6/4/2007 3
Long Beach 6/18/2007 24
Main Beach 12/3/2006 50
Main Beach 1/8/2007 521
Main Beach 3/10/2007 91
Main Beach 5/2/2007 2
Main Beach 7/23/2007 39
New Beach 1/23/2007 8
Short Beach 12/3/2006 10
Short Beach 6/18/2007 1
Snook Beach 1/8/2007 75
Snook Beach 6/18/2007 119
Snook Beach 7/30/2007 27
Third Beach 12/3/2006 30
Third Beach 7/23/2007 10
850 Southeastern Naturalist Notes Vol. 9, No. 4
of a dense patch of Blackbead flanked by abundant flowering herbaceous species
such as Melanthera nivea (L.) Small (Snow Squarestem) and Cakile edentula (Bigelow)
Hook (Coastal Searocket).
On 23 January 2007, we searched about 30% of the uplands on Boca Grande Key
and observed 100 adult Miami Blues over a 1.5-hr period. We performed systematic
counts (each >3 h) on 3 February, 9 April, and 23 July 2007 and observed 441, 51,
and 89 adult Miami Blues, respectively.
On 3 December 2006, Miami Blues were abundant on Main Beach. We counted
50 adult Miami Blues along ≈30 m of the 1065-m dune before a rapidly falling tide
forced our departure. We performed systematic counts on 8 January (4.5 h) and 10
March 2007 (3.4 h) and counted 521 and 91 adult Miami Blues, respectively.
Partial searches of Main Beach (2 May 2007) and Boca Grande Key (28 May and 18
June 2007) revealed only 2, 0, and 1 Miami Blues, respectively. We observed little new
leaf growth and no flowering of the Blackbead on these 2 islands after February 2007.
Although the dune/coastal strand on Snook Beach is considerably smaller than
that of Main Beach and Boca Grande Key (Table 1), we counted 75 and 119 Miami
Blues, respectively, during >2-h searches on 8 January and 18 June 2007. Thus, it is
an important area for the Miami Blue.
New Beach had a very short beach (85 m) with a narrow coastal strand. For >2
hours, we searched the entire area for Miami Blues and their known host plants. We
found a tiny Caesalpinia bonduc, (L.) Roxb. (Gray Nickerbean), a known Miami
Blue host plant (Minno et al. 2005), and only five small Blackbead, four of which
were aggregated in one area. Although herbaceous food plants were abundant and
flowering, only 8 Miami Blues were observed. We believe a paucity of host plants
was a limiting factor at this site.
On East Cove, a very narrow (<2 m wide) dune was bordered by such a dense tangle
of live and dead Blackbead that we could not even enter the coastal strand. Twelve adult
Miami Blues were counted on the strand’s periphery during a 1.5-h search.
On Short Beach, the once-abundant stands of Blackbead (T. Wilmers, pers.
observ.) were nearly obliterated by Hurricane Wilma, with only scattered stressed
individuals remaining. We counted 10 Miami Blues on the extreme south end of the
island, where a narrow upland extended some 75 m landward of the dune.
At Third Beach, Blackbead was scarce and limited primarily to the southwest
side of the beach. Despite this, 30 Miami Blues were counted there during a brief
search (<1 h) on 3 December 2006.
The dune on Long Beach was the only one in the study area that had been blanketed
by a thick mat of calcareous Halimeda algae washed ashore by Hurricane
Wilma’s storm surge (T. Wilmers, pers. observ.). This algae deposit was likely a
factor for the very slow recovery of the dune vegetation, which even by July 2007
remained sparse. Long Beach was far too large for us to survey, and our work there
was limited to a small area. We counted 24 Miami Blues along 500 m of the dune/
coastal forest interface on 18 June 2007. Given the great length of its dune/coastal
strand, Long Beach has the potential, once the habitat fully recovers from hurricane
damage, to harbor more Miami Blues than any other surveyed site.
We found no Miami Blues on east Man Key or Woman Key. These islands had
abundant nectar sources, but a paucity of host plants.
No Miami Blues were found in the Great White Heron NWR. No host plants
were found on northwest Sawyer Key, but herbaceous nectar sources were abundant.
Northeast Sawyer Key harbored a few small Blackbead and several Gray Nickerbean
but few nectar sources. Johnston Key (west GWHNWR) contained a dearth of nectar
2010 Southeastern Naturalist Notes 851
sources and no host plants. Johnson Key (east GWHNWR) had only a few scattered
Blackbead and few herbaceous nectar sources. The tiny upland area (10 x 20 m) on
Porpoise Key lacked any herbaceous nectar source and was too small to harbor a
Miami Blue population. Snipe Point contained scattered Gray Nickerbean and Blackbead
and abundant herbaceous nectar sources.
Including Blackbead, adult Miami Blues visited the flowers of nine plant
species for nectar (Table 3). Of these, four were woody plant species: Argusia
gnaphalodes (L.) Heine (Sea Lavender), Suriana maritima (L.) (Bay Cedar), Erithalis
fruticosa (L.) (Black Torch), and Blackbead.
All of the Miami Blue colonies in KWNWR were on remote islands (19 to 36
km from the nearest habitation, Key West) having federal wilderness designation.
Mosquito spraying, which is potentially detrimental to the Miami Blue (Carroll and
Loye 2006) and widespread on the mainline Florida Keys (islands linked by roads),
has never occurred on or near any of the islands in the KWNWR. All areas occupied
by the Miami Blue had coastal strands and dunes fronted by beaches. Important requirements
in such settings were apparently the host plant, Blackbead, and other
abundant nectar sources. Grey Nickerbean, the main host plant used by the Miami
Blue at Bahia Honda State Park (Carroll and Loye 2006), was rare in KWNWR,
with only a few small plants on Boca Grande Key and the Marquesas Keys. Even
before Hurricane Wilma, the plant was not common in the KWNWR (T. Wilmers,
The growth stage of Blackbead, coupled with abundant nectar from herbaceous
plants, likely influenced Miami Blue abundance. The highest counts on both Boca
Grande Key and Main Beach occurred when Blackbead was flowering profusely
and producing new leaves. During late November 2006 through January 2007, an
unusually intense profusion of Blackbead flowering occurred. During this period, we
frequently observed Miami Blues nectaring on Blackbead flowers (Fig. 1).
Female Miami Blues laid eggs on Blackbead flower buds (Fig. 1) and emerging
Blackbead leaves. We did not observe any evidence of egg-laying on or larval
consumption of mature Blackbead leaves. Thus, even if abundant suitable nectar
sources were available year-round, Miami Blue numbers would be regulated by the
availability of young Blackbead leaves and buds for egg-laying.
Although Hurricane Wilma severely damaged or killed many Blackbead, the storm
likely enhanced Miami Blue foraging habitat, if only temporarily, on both Boca Grande
Key and Main Beach by removing the extensive dense stands of Uniola paniculata
L. (Sea Oats) adjacent to the coastal strand. This plant is neither a nectar source nor
host plant for the Miami Blue. In its place grew an abundance of early successional
Table 3. A list of plants used as a nectar source by the Miami Blue in the Key West National
Scientific name Common name
Argusia gnaphalodes Sea Lavender
Alternanthera flavescens Yellow Joyweed
Cakile lanceolata Coastal Searocket
Erithalis fruticosa Black Torch
Heliotrophium curassavicum Seaside Heliotrope
Pithecellobium keyense Blackbead
Melanthera nivea Snow Squarestem
Suriana maritima Bay Cedar
Sesuvium portulacastrum Sea Purslane
852 Southeastern Naturalist Notes Vol. 9, No. 4
herbaceous plants that were flowering profusely and providing plentiful nectar for the
Miami Blue during the early months (December–February) of our study.
Further, in the coastal strand, the hurricane created open patches in what had been
a shaded woody understory (T. Wilmers, pers. observ.). Herbaceous plants emerged
in these open patches, providing additional nectar for the Miami Blue. (T. Wilmers,
That the plentiful new Blackbead leaves and buds for egg deposition were present
concurrently with abundant nectar from the flowers of both Blackbead and herbaceous
plants lead us to believe that habitat conditions after Hurricane Wilma were particularly
favorable for Miami Blues from December 2006 to February 2007 on Boca Grande
Key and Main Beach. By March, Blackbead was no longer budding or flowering, and
by May we observed that herbaceous plant flowering had decreased drastically on
both islands. During the latter month, we found 0 and 2 Miami Blues on Boca Grande
Key and Main Beach, respectively. Ultimate factors regulating butterfly populations
remain unresolved (see McLaughlin et al. 2002). Minno and Minno (2009) noted that
butterfly metapopulations in the Florida Keys rise and fall dramatically, with core
populations expanding greatly during exceptionally favorable conditions, resulting in
dispersal and temporary colonization of even marginal habitats.
That Miami Blues were found at such a large number of sites in the Marquesas
Keys is fortuitous. These islands are remote and seldom visited by humans. How
frequently Miami Blues disperse between these islands is unknown. The proximity
and circular arrangement of the islands may afford some measure of protection to the
butterflies during tropical storms and moderate hurricanes.
Threats. Boca Grande Key is >10 km closer to Key West, a tourism hub, than the
nearest island in the Marquesas Keys. Human visitation is sometimes high on Boca
Grande Key, particularly on weekends (T. Wilmers, unpubl. data), and trampling of
dune vegetation has been a long-standing problem. On this island and the Marquesas
Keys, the large amount of dead vegetation intermingled with live Blackbead makes
the threat of fire, natural or man-caused, a significant threat to the Miami Blue and
its habitat. Illicit campfire pits have been found many times over the past 2 decades
in both areas (T. Wilmers, pers. observ.).
Rising sea level is an acute threat at all the sites that harbored Miami Blues. Six
of 8 occupied sites were <1 m above sea level—including Main Beach, where the
largest number of Miami Blues was observed—and none was >2 m. Pronounced
beach erosion, undercutting, and narrowing the dunes and/or coastal strand, was
particularly evident at Short Beach and Boca Grande Key.
Although lesser hurricanes like Hurricane Wilma may temporarily enhance
Miami Blue habitat by promoting early successional growth, a stronger hurricane
could extirpate this species in KWNWR. The last Category 4 or higher
hurricane in the Florida Keys was Hurricane Donna in 1960, but its strongest
winds occurred more than 130 km from Boca Grande Key. Although Hurricane
Wilma (2005) was at most a Category 3 hurricane in the Florida Keys (National
Oceanic and Atmospheric Administration 2005), its winds and storm surge washed
away a part of the southern dune on Boca Grande Key, creating a breach that has
since progressively widened. The number and severity of hurricanes are projected
to increase because of global warming (Webster et al. 2006), ominously further
threatening the Miami Blue population in KWNWR.
Acknowledgments. We are grateful to the Florida Keys Audubon and the Friends
and Volunteers of Refuges of the Florida Keys National Wildlife Refuges for financial
support. P. Hughes, K. Meyer, and G. Zimmerman provided helpful comments on an
2010 Southeastern Naturalist Notes 853
early draft of the manuscript. M. Minno provided extensive, insightful comments that
greatly improved the manuscript. We thank E. Saarinen for editorial assistance. A.
Morkill, Project Leader of the Florida Keys National Wildlife Refuges, unwaveringly
supported our efforts.
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