COMPARATIVE SUCCESS OF MONARCH BUTTERFLY MIGRATION TO OVERWINTERING SITES IN MEXICO FROM INLAND AND COASTAL SITES IN VIRGINIA

2008·7.8 MB·English

by  Larry J Brindza

Volume 62, Number 4 1S9
JournaloftheLcpidoptcrists’SocicU/
62(4),2()()8.189-200
COMPARATIVE SUCCESS OF MONARCH BUTTERFLY MICRATION TO OVERWINTERING SITES IN
MEXICO FROM INLAND AND COASTAL SITES IN VIRGINIA
Larry Brindza,
J.
9701 IlurrCourt, Burke,VA22015
Lincoln P. Brower,
DepartmentofBiology,SweetBriarCollege,Sweet Briar,VA24595;email:lirower@,sbc.edu
Andrew K. Davis,
Warnell SchoolofFore.stryandNatural Resources, UniversityofCeorgia,AthensGA30602
AND
Tonya Van Hook
DepartmentofBiolfjgy,Sweet BriarCollege,Sweet Briar,VA24595
ABSTRACT.PriortaggingstudiesatAtlanticcoastalsitesinNewJerseyandVirginiasuggestedthatfall migrantmonarchButterflies(Danaus
plexippus L., Nymphalidae; Dauainae) oftheeastern North American population havelowerrecoveryrates atovenvinteringsitesin Mexico
comparedtotheoverall recoveiwratesreportedBvMonarchWatchformonarchstaggedthroughoutthelatesummerBreedingrange. Herewe
presenttheresultsofthefirst quantitativestudythatcomparestheproBahilityofrecapturein Mexicoofmonarchstaggedatcoastal siteswatli
inlandsitesthatareeastoftheAppalachian VIountains. Duringthe2()()l-2()06fallmigrations,wetagged 1,008monarchsalongtheAppalachian
piedmontinVirginia,ofwhich 13(1.29%)were recoveredin Mexico. Incontrast,outof 1,216taggedatAtlanticcoastal locationsin Virginia,
only2(0.16%)wererecovered. Thiseightfoldlowerrecapture rateofthecoastal monarchsis highlysignificant. Thedataalsoindicatedthat
mf)narchs migratingalongthepiedmontontheeasternsideof theAppalachiansare nearlyaslikelyto reach Me.xicoasarethosethat migrate
westoftheAppalachians. WeconcludethatmigratingalongtheAtlanticcoastperseismoreriskwthan migratinginlandeithereastorwestof
theAppalachians. TherecoverydataalsodeterminedthatBothsexesofthepiedmontmigrantsreached Mexico,But,torunknown reasons,fe-
malesweremoresuccessful. SincecoastalmigrationoccursregularlvandinvolvesveiylargemmiBersofmonarchs,theAtlanticcoastisnotan
aberrantmigratoryrouteastheUrquhartsmaintained. Whythendofewercoastalmigrantsreach Mexico? Somecontinuesouthwardandmay
becomeincoiporatedinandhelpsustainBreedingpopulationsinsoutli Florida,CubaandperliapsinotherCaribbeanislandsandtheYucatan.
Toexploreotherpossiblereasonsforthelowersuccessofcoastal monarchsinreaching Mexico,wecomparedwinglengthsandwetmassesof
483inlandwith morethan 140coastalmonarchs. Thelatterhadslightivbutsignificantlysmallerwinglengthsand, even afteraccountingfor
variationinwinglength,theyweigheillessthantheinlandmonarchs.Thelowerwetmassreflectslowerlipidand/orlowerwatercontentswhich
wearguemaybeaconsequenceofanthropogenicdegradationofmuchofthenativefloraandnectarsourcesalongtheAtlanticcoast. W'econ-
sidervarioushyjrothesesthatmayaccountforthecoastalmigrants'smallerwingsthantheinlandmigrants,includingthecontroversialideathat
thelongerwingedmigrantsmaylieblownouttosea.
Additionalkeywords: taggingandrecapturerates,wetmass,winglength,nectaravailability';Atlanticcoastaleco.systemdeterioration,liskw
fallmigrationroute.
Qualitative knowledge derivedfrom the recoveries of the Atlantic coast, Walton (1999), Walton & Brower
tagged fall migrant monarch butterflies {Danaus (1999) and collaborators initiated a tagging program in
plexippus, L.) has indicated that their success in Cape May Point, New Jersey. In the fall of 1998, they
reaching the overwintering areas in Mexico is tagged 7,541 monarchs (numbercorrectedby Browerct
substantially greater when the butterflies are tagged al. in prep), of which seven were subsequentlyfound at
west comjrared to those tagged east ofthe Appalachian the Mexico ovenvintering sites, a recapture fre(jnency
Mountains (Urejuhart & Urquhart 1979a, b; Unjuhart of0.093%. In 1998 Garland & Davis (2002) started a
1987; Monarch Watch 2006). An unexplored aspect of second coastal tagging program on the southern tip of
this difference iswhether monarchs migratingalongthe the Dehnarva Peninsula in Virginia. They released
Atlanticcoastpersehave alowerprobabilit)'of reaching 2,190 monarchs over three years (1998-2000), ofwhich
Mexico, or whether all monarchs mieratino; east of the one was found in Mexico, a recapture frecjnency of
Appalachians, including the piedmont and the coastal 0.046%. In contrast, of an estimated 1.1 million
areas, are less successful. monarchs tagged by Monarch Watch participants from
Toobtain (jnantitativedataonthe fall migration along 1992 through 2006 in the eastern US and southern
190 Journalofthe Leridopterists’ Societt'
Canada, 12,()()() to 14,()()()were recaptured in Mexico, a inonarchs, what factors might account for the
recoveiy rate of 1.09% to 1.27%i (Taylor pers. coin. differences?
2007; Monarch Watcli 2006). Using Monarch Watch's To answer the first two questions, we compared the
lowest recoveiw rate as a rough estimate ofthe overall nnmber ofrecaptures in Mexico ofinonarchs collected
eastern rate and dividing it hyeach of the above coastal and tagged along the eastern edge ofthe Appalachian
rates (1.09% / 0.093%. = 1L7; and 1.09%. / 0.046%) = piedmont in northern Virginia with recaptures of
23.7) indicates that tlie coastal inonarchs have only inonarchs collectetl and tagged during the same years
1/12th to l/24th of the chance of being recaptured in along the Atlantic coast in southern Virginia. We
Mexico (see also Taylor, in McNeil 2006). addressedthethirdquestion bycomparingwinglengths
This nnich lower prohabilitv of coastal inonarchs and adult weights (wet mass) of snb-samples of the
reaching Mexico raises fourquestionsthatwe address in tagged inland and coastal inonarchs. We addressed the
this paper. First, are all inonarchs that migrate along fourth question by relating the wing length findings to
the eastern side of the Appalachians less likely to reach greater coastal losses due to wind and possible other
Mexico than inonarchs that migrate west of the causes, and by relating the wet mass findings to
Appalachians? Or, second, do those inonarchs that anthropogenic changes in habitat quality along the
migrate along the piedmont that stretches eastwards Atlantic coast.
from the Appalachians to the coastal plain (Atwood
Materials and Methods
1940; Raisz 1957) haveasuccess ratesimilarto migrants
westofthe Appalacliians? Third, ifthe coastal migrants Collecting sites. Over six years (2()()l-2()06)
per se are less successful, do these inonarchs exhibit betw'een the last week ofAugust and the last week of
differences in physical properties from the inland Octolier, Brindza collected fall migrant inonarchs from
piedmont migrants? Fourth, if there are physical one or more coastal and inland sites in Virginia. The
differences between the coastal and inland piedmont collection dates overlapped with the timing ofthe fall
Fig. 1. Location ofcoastal andinlandstudysites in eastern\drginiaandaveragewet massesoffallmigrantmonarchs ineastern
NorthAmerica. Thecoastalsiteswerelocatedonthesoutherntipofthe DelmawaPeninsula(smallsquareinthelowerinsetbox).
The inlandsiteswerecenteredaroundthetownofVVoodbridge onthepiedmontoftheAppalachians (small circle inthe lowerin-
setbox).Thenumbersonthemapindicateaveragewetmasses (mg)ofmalesandfemalescombinedoffall migrantmonarchsfrom
thisstudyandfromotherpublishedstudies(BrownandChippendale 1974;GiboandMcCurdy1993; Borlandetal. 2004). Theup-
per left inset shows the appro.ximate range ofthe eastern North American monarch population, with the location oftheMexican
oveiAvinteringarea.
.
Volume 62 Number 4 191
,
migration along botli the Atlantic coast in Virginia base to standardize the common and scientific
(Garland & Davis 2002; Gihhs et al. 2006) and through nomenclature (Anon. 2007a). Gomposites (A.steraceae),
an inland site on the eastern edge of the Bine Ridge on which many butterflies were nectaring, incinded
Mountains at Sweet Briar Gollege, Virginia, about 275 bearded beggar ticks {Bidens aristosa (Michx.) Britt.),
km west ofthe coastal area (BroweretaJ. 2006). In the woodland sunflower {HelUmthus divaricatus L.), bull
fall of 2001, Brindza concentrated on tagging the thistle {Cdrsiiiin viilgare (Savi) Ten.), other thistles
butterflies and, from 2002 through 2006, he also {Cdrsiiiin spp.), false boneset (BrickeUia eupatorioidcs
weighed and measured the forewing lengths ol sub- [L.] Shinners),white snakeroot (Eupatoiiiun nigosii)}) =
samples ofthose that he tagged and released. Ageratina alfissima (F.) King & H.E. Robins), seaside
The coastal samples were collected at Kiptopeke goldenrod (Scdidago seuipcrvirois F.), Solidago spp.,
State Park, on the Eastern Shore of Virginia National hyssopleaf thoroughwort {Eiipatoriiim hijssopifolhnn
Wildlife Refugeand Fisherman Island NationalWildlife F.), late flowering thoroughwort {Eiipatoriinn
Refuge. These areas are surrounded to the west by serotiiium Michx.), orange cosmos (Cosmos stilj)luirctis
Ghesapeake Bay and to the east and south by the Gav.) and garden cosmos (C. hipimiatiis Gav.). The
Atlantic Ocean (Fig. 1). Both are good locations for shrubs on which theywere nectaring included butterlly
capturing migrating monarchs because of the tunneling bush (Biiddleia davidii f^., Buddleiaceae), Russian olive
effectofthe peninsula (Garland & Davis 2002). (Edacagnus angiistifolia F., Elaeagnaceae), abelia
The inland monarchs were collected along the (Ahclia ahelia R. Br., Gaprifoliaceae), lantana, (Eaiitdiia
Piedmont about 190 km northwest of the coastal area camara L., Verbenaceae) and groundsel tree (eastern
within a 10km radiusofWoodbridge,VA (3S"3S' OS" N, baccharis, Baccharis halimifoUa F., Asteraceae).
77“ 15' 44"W), 20-30 km SWofWashington. D.G. (Fig Tagging. Brindza tagged the butterflies within fO
1.). The collecting site in 2001 was solely in fjorton, minutes of capture using nnmbered adhesive tags
while from 2002-2006, the butterflieswere collected in pro\’ided by Monarch Wkitch. 0\er the six years, he
Forton, Gunston Gove, the Occo(|uan Bav National tagged and released 1,216 monarchs in the coastal sites
Wildlife Refuge and Mason Neck State Park. and 1,008in the inlandsites (Table 1). We subsequently
Collectingmethods. Brindzanetted most monarchs determined those recoxered at the ox'enx'intering sites
while they were nectaring on several species of in Mexico by consulting the Monarch Watch tag
composites growingin open fields orin flowerbeds, and recox'eiv data base (http:/A\a\'\\xmonarchwatch.
on cultivated and native shrubs. About 2% were cf)m/tagmig/rec()veI'ies.htm)
collected from roosts. Immediately after capture, he Weighing and measuring. lOuring 2002-2006,
removed each monarch from the net and placed it in a Brindzameasured the left forewinglengthandwet mass
5.1 X 7.6 cm glassine envelope. Successive captures of snb-samples of the monarchs that he tagged (Figure
were accumulated for about 10 minutes in a small 2). He measured left forexx'ing length follo\\4ng the
plastic bo.x and kept out ofdirect sunlight. protocol of Brewer & Van Hook (in prep.). This
Brindza made all plant identifications based on measures (mm) the straight line distance on the x'entral
Newcomb (1977), Peterson & McKennv (1968) and surface of the forewing from the forewing tip to the
Fobstein (1990). We followed the USDA plant data xx'hite dot on the base of the \\4ng xxdiere the xx'ing
Table 1. Summarvottlienumberofmoiuirclibutlterlliestaggedduringtlii.s.stiidx'atcoastal andinlandsitesinVrginia.
Coastal Inland
Year Males Females Total % Female .Males Female.s Total % F'emale GrandTotal
20t)l 231 182 413 44.1 .374 151 525 28.8 938
2002 67 18 85 21.2 41 22 6.3 .34.9 148
200.3 34 20 54 37.0 35 21 56 37.5 no
2004 7 4 11 36.4 2 0 2 0.0 13
200,5 14 17 31 .54.8 99 64 163 39.3 194
2006 370 252 622 40.5 134 65 199 .32.7 821
TotalTagged 723 493 1216 40.5 68.5 .323 1008 ,32.0 2224
192 Journalofthe Leriooptehists’ Societt'
attaches to the thorax. All measurementswere madeto
mm
the nearest 0.1 with handheld Mitutoyo digital
calipers (Ben Meadows Co., Janesville, VVI). Brindza
also measured wet mass, rounded to the nearest mg,
using a portable electronic balance with an accuracyof
0.001 g (Acculah, Model PP2060D, Sartorius Group,
Gottingen, Germany). The balancewas recalibratedon
each day of use. Throughovit the study, the length of
time between capture and measuring and weighing
individual monarchs did not exceed 15 minutes.
Weighing tliem as soon as possible after capture is
imperative to avoid mass (weight) loss through
desiccation.
Stati.stical analyses. Weused Statistica6.1 software
(Statistica2003) forouranalyses. We usedchi-squareto
test for significant differences in the nnmbers of
recaptures in Mexico ofmonarchs tagged at the inland
vs the coastal sites. We also used chi-scpiare to test for
differences in the numbers oftagged males andfemales
in reaching Mexico. We used ANOVA to e.xplore the
factors inffueuciug variation in monarch wing lengths
Fic:. 2. Dislrihution oi (A) lorewing lengths (niin) and (B) and wet masses. With wing length or wet mass as the
wet masses (mg)oi thecoastal andinland monarclLS.
dependent variable, we included site (inland and
W
Inland M Coastal coastal), sex (male and female), and year (2002, 2003,
A. 2005 and 2006) as categorical independent variables.
52.8 The2004datawereexcludedfrom theanalysesbecause
^ oftlie veiy small sample sizes. All two-way and three-
524
E way interactions were initially included in the model,
^ 52.0 and dropped if not significant. We used analysis of
sz covariance to examine the factors affecting monarch
Oc) 51.6 mass, v\4th winglength as a covariate to account for the
CD
-I 51.2 fact that mass is influenced by butterfly size {i.e.
CD)
forewTug length).
^ 50.8
504 Results
Recaptures in Mexico. Thirteen of the 1,008
50.0
(1.29%) butterflies tagged at the inland sites were
B. recaptured while only 2 of 1,216 (0.16%) were
600 recaptured from the coastal sites (Tables 1 and 3). This
^
580 eight-fold difference in recapture rate is statistically
OE) 560 significant (chi-square = 10.41, 1 df, P < 0.001). Our
datathus indicatethat monarchs migratinginlandacross
540
^CD the piedmont east of the Appalachians have a much
520
higher probability ofbeing recaptured in Alexico than
dothose nrigratingalongthe Atlantic coast.
480 Our low coastal recapture rate was l.S times higher
than that found by Walton & Brower (1999) in Gape
460
May (0.093%) and 3.6 times higher than that found by
440
Garland and Davis (2002), on the southern tip of the
2002 2003 2005 2006 Delmarva Peninsula in Virginia (0.046%). Our higher
Fig. 3, (A) Average\\'inglength and (B) averagewet mass of value is likely due to the fact that the majority of our
monarchs for the four years (2002-2(K)6, e.xcluding 2004) for
both inlaml and coastal sites. Bars indicate 9.5% confidence in- monarchs were tagged during the fall preceding the
temils. Januaiy 2002 storm that killed nearly one quarter ofa
Volume 62, Number 4 193
billion monarchs in two colonies (Brower ef aJ. 2004) significant main effects and interaction terms (Table 5),
and resulted in an all time high tag recoveiy rate in most notably, the main effects of year (F3^,n„=S.6,
Mexico (Monarch Watch 2006). p<0.()01), sex (Fjg||,=4.4, p<().037), and wing length
There was a deficiency of females each year in all (Fjgg,,=lS2.5, p<().()()l). Males weighed significantly
samples exceptforthecoastal samplein 2005 (Table 1). more than females (Table 2B), 552 mg vs 511 mg
For the inland samples tagged in 2001, there were 374 overall), and not surprisingly, the effect ofwing length
males and 151 females, i.e. 29% females. Of the 12 was positive (i.e.monarchs with longer wings also had
inland monarchs recaptured in Mexico that season, 7 of greater mass). There was a significant interaction of
12, i.e. 58% were females. Tims there was a reversal in site“year (Fggg„=5.7, p=().001. Table5). Thisinteraction
the sex ratiowith twicethe frequencyoftagged females effect is evident in Fig. 3B, in that the monarchs from
recaptured (chi-square = 5.12, 1 d.f., P < 0.025) the coastal siteweighed less than those from the inland,
indicating that both sexes reached Mexico from the but the magnitude of this effect depended on tlie year,
inland route, but that females were substantially more being smaller in 2006 than in 2002. Further, the
successful than males in doingso. difference inwet mass between siteswas not due to the
Wing length. The data for the coastal and inland size difference in monarchs, as indicated by an analysis
samples are shown in Figs. 2A and 3A. Two way of covariance in which the effect of wing size was
ANOVA (Figure 4) analyzed differences for site, year included in the mass model. To elucidate this point
and sex for the 617 monarchs that we measured. We further, we plotted (Fig. 4) the average residual mass
found no significant (P > 0.10) two-way interaction (from the significant linear regression of mass versus
terms. When these were dropped, the main effects wing length) of both sites so that the difference in
revealed significant effects of both year (F^gjj=10.5, weights, afterwinglength is accounted for, can be seen.
p<0.001) and site (F^pjj=4.0, p=0.046). Tnkey’s post- Thus when size is removed, the difference in mean
hoc comparisons indicated that monarchs captured in residual mass between sites is significant (t-test, df =
2002 were significantly smaller than in all other years. 625, t= 2.31, p = 0.021). Thus the average wet mass of
Theellectolsiteisevidentin Figure3A,with monarchs the coastal migrants (496 mg) was 9.6% less than the
slightly but significantly larger at the inland sites on inlandmigrants (.549 mg) andwas lowerthan that found
average and for three ofthe four years. At the inland in several other studies (Brown & Chippendale 1974;
sites, the average for both sexes was 52.1 mm, while at Gibo & McCurdy 1993; Borlandetal. 2004) as shown in
coastal sites itwas 51.3 mm, adifference ofabout 1.5%. Figure 1.
Body mass. The data for the coastal and inland
Discussion
samples are shown in Figs. 2B and 3B. For wet body
mass, the final model contained several highly The datafrom this studyin Virginiademonstrate that
monarchs captured during the fall migration along the
Atlantic coast differed in three significant ways from
those migratinginlandacross thepiedmontbetween the
o) 15 Appalachians andthecoast. Relativelyfewofthe coastal
r migrants succeeded in reaching the oveiAvintering sites
10
in Mexico, they had slightly smaller wing lengths and
CO II
they had lower wet masses. These results have major
^ 0 ^ implications for a more complete understanding of the
a: fall migration oftheeastern North Americanpopulation
Vi 5 ofthe monarch butterfly.
Vi
<0 10 Migration east and west of the Appalachians.
Based on their tagging studies, Urquhart & Urqnhart
ic
(1979a, b) and Urqnhart (1987) maintained that
Inland Coastal monarch migration along the Atlantic coast is
Monarchs Monarchs "aberrant". Briefly, they contended that variable
munbers of fall migrants are blown by westerly winds
overthe Appalachians to the east coast. They reasoned
Fig. 4. Conipari.son ofaverage residual mass (residuals from
a linear regression of mass versus wing lengtli) of monarchs that these avoid flying over the ocean with most
from both inland andcoastal sites. The differenceis significant continuingto migrate south alongthe coast into Florida
(t-test, df=62.5,t=2.31,p=0.021). Barsindicate9.5%confidence and thence into the Caribbean, without reaching the
intervals.
oveiwinteringsites in Mexico. The Ur(|uharts' aberrant
194 Journalofthe Lepidopterists’ Society
migration hypothesis, together with the much low'er asyve haveconfirmed, migrationalongthecoastperseis
frequenciesofrecapturesin Mexicoofmouarchstagged tar less successful, flowever, being less successful does
eastcomparedtothosetaggedw'estoftheAppalachians not necessarily mean that the coastal migration is
liy Monarch Watch (Taylorpers. comm.. 2007; Monarch aberrant, adescriptorthatwe consider misleading.
Watch 2006), has led to the general assumption that Rejection ofthe aberrant migration hyjjothesis.
monarch migration anv\\4iereeastoftheAppalachiansis In contestingthe aberrant coastal migration hy|)othesis,
a less successful strategy in reaching Mexico. This Walton & Broyy'er (1996, 1999) reported that at least
contention wtis reinforced by an analysis of40 years of some tagged coastal mouarchs do succeed in making it
recapture data (Roggctal. 1999) showTugthat migrants to Alexico, asyvehaveagain shoyy'iiinthispaper. Walton
west ofthe Appalachians likelydo get hkmm eastyvards, & Broyy'er also reemphasized that the coastal migration
but they are in some yvay able to compensate tor this has occurredregularlysince ityvas describedin the 19th
yyand drift and, as some birds and dragonflies do centui'v and often iny'oh'es spectacular numbers of
(Richardson 1990; Svrgley 2004), they' reorient to a butterflies (Broyy'er 1995). This has been confirmed
sontliyy^esterly course leading them to Mexico (see also (|uantitatively by fifteen consecutive annual censuses in
Iloyvard 2007). Cape May, Neyv Jersey begun in 1991 (Walton &
Based on the results ofour study', this general model Broyy'er 1996; W'alton et al. 2005) and by nine annual
requires modification. W'e have determined that coastal censuses in Chincoteague, Virginia, 117 km
migration east ofthe Appalachians along the piedmont south of Cape May (Gibbs et al. 2006). Further
mav be as snccessinl as the migration yvest of the eyidenceof the large magnitudeof thecoastal migration
.'Appalachians. In contrast, as maintainedin thepast and includes reports of nocturnal roosts of over 10,000
T.yiiLE2, A. Femaleanilmalemean mass(wetweight) anilsize(\vin«length)comparisonsbehveenCoastaland Inlandcollectionssitesin
\’A. 2()02-2()06. B. Oierall mean massanilsizecomirarisons: 1)Coastalversus Inland,combiningallyearsandsexesand2) maleversus
lemalecombiningally'earsandbothCoastaland Inlandsites. Datafor2004arenotincludedbecauseofveivsmallsamplesizes.
A. WET\t’ElCHT(mg) WINGLENCTIl(mm)
Females Males Females Males
Year Coastal Inland Coastal Inland Coastal Inland Coastal Inland
2002 Mean 449 557 524 593 49.9 .50.7 51.3 50.9
STD 49.7 83.3 .54.4 68,1 2.3 2.1 27 2.1
N 14 22 31 41 14 22 34 41
200:3 Mean 495 539 483 585 52.1 51.9 51.1 52.3
STD 59.8 65 I i 88.4 1.4 1.1 2.0 1.9
N 15 21 27 35 15 21 27 35
2005 Mean 487 507 492 561 52 51.8 50.9 ,52.6
STD S4.6 95.9 93 88.2 2.2 2.5 2.4 1.9
N 17 64 14 99 17 64 14 99
2006 Mean 521 514 516 554 .52.3 52.3 51.8 .52.5
STIY 43.2 t1 72.7 73.8 1.7 2.1 0,9 2.0
N 6 65 9 1.34 6 65 9 134
B WETWEIGHT(mg) WINGLENGTII(mm)
Coastal Inland Coastal Inland
1.AllYrs& Mean 496 549 51.3 ,52.1
Both Sites STD 71.4 85 2.2 2.1
N 133 481 136 481
Females Males Females Males
2. AllYrs& Mean 511 552 51.8 52.1
BothSexes STD 82.8 82.8 2.2 2.1
N 224 390 224 393
Volume 62. Number 4 195
iiionarchs onCliincoteague (Gibhspars, coinni.) andon However, it is relevant to point out tliat natural
Cape May (Smith 2007). selection is a strong evolutionaiw force that has shaped
Given the fact thatthe Atlanticcoastal migration is an the flight dynamics of both birds and insects along
integralpartofthe monarch's fall migration, whatis the coastalenvironments, and, onoceanicislands, has ledto
fate of migrants of the eastern North American flightlessness in many lineages. ft is also well
population that do not make it to Alexico? Cardenolide established that insects lose control of their direction
fingei'printing indicated that some migrate into south and velocitywhen they fly up out of the slower mo\ing
Florida where they become incorporated into local air in the Iroundaiy layer near the ground and can be
breeding populations on the eastern edge of the carriedawaybythewind (pp. 298, 324, in Dudley2()0();
Everglades (Knight 1998). Cardenolide fingeqorinting Alexander 2002). However, Robert Dudley (pers.
togetherwith isotope marker analyses determined that comm.), contends that the opposite slumld be true,
still others continue across the Caribbean to Cuba namelythatthe largerwinged indi\4duals shouldhave a
where they also liecome incoiporated into local bettei' chance of fighting their way back in from the
breeding populations (Dockx et al. 2004). Those that ocean tothe coast. Dudley& Syrgley(2008) also found
may reach tlie Yucatan or any ofthe Antillean islands that several neotropical migrant butterflies reduce their
(Urquhart 1987) may help sustain these tropical flight speed as their lipitl resei-ves deplete. Thus, there
populations. However, the abilityofall these butterflies may be an inteqrlay between size and mass in the
to remigrate northwards the following spring is nil cfjastal monarchs, resultingin the largerindividuals that
because, in becoming reproductive under the high have a depleted lipid mass ha\ing to slow down, and
tropical temperatures, theylosetheirmigratoiycapacity' therefore loweringtheir abiliWto fight the wind.
and will not l)e aide to live for the five or more months While we have no direct evidence, our wing length
until spring arrives alongthe Gulf Coast (Brower 1995; hxqrothesis is consistent with obsenxitious made by
Zemaitis 2005). On the other hand, some of those Schmidt-Koenig (1993) alongthe Atlanticcoastline that
coastal migrantsthat regain the southwesterlymigratoiy monarchs avoid fl)4ng over large bodies ofwater unless
trackdo make it to the Mexican ovenvinteringsites and the direction and speed of the winds are favorable.
have the opportunitv to remigrate back into the Gibbs (2007) alsoobsened monarchs' strongreluctance
southern USA the followingspring. to lly southwesterly across the Chesapeake Bay when
In light (d all these recent findings, we reject the the winds were unfavorable. Tliat migrating monarchs
aberrant migration hvpothesis andwecannotagreewith are sensitive to unfavorable winds is also evident from
Taylor's contention (in McNeil Jr. 2006) that monarchs theirresponsetocross-windsbyll)inglowtotheground
migrating along the coast are "toast." However, the (Schmidt-Koenig 1985; Davis & Garland2002; Garland
lower recapture rates, shorter wing lengths and lower & Davis 2002), or by simplypausing their migration to
wet massesofthecoastal migrants doindicate thatthere wait for better conditions to resume fl)iug and soaring
are negative factors affecting these monarchs' ability to (Schmidt-Koenig 1985; Davis & Garland 2004). fshiiet
reach Mexico, What might these negative factors be? al. (1992), working along the Gulf Coast south of
Risk of being l>lown out to sea favors shorter Tallahassee, Florida, counted the numbers of fall
wing lengths. When one considers the distances tlie migrants thatwere flyingoverthe ocean and found that
monarchs may fly, coastal migrants must be severely the number Hying inland exceeded the number living
challenged by winds. The Atlantic coastal habitat out. Theyinteipretedthis as evidence for reluctance to
extends for2,700 miles from Maine to Florida, includes sustain Hight across tlie Gulf
the Florida Gulf Coast, and continues westward and Energetically contending with the coastal
southward to the border ofTexas and Mexico (Beatley environment. One hypothesis toe.xplain the lovv'erw'et
etal. 2002). Weproposethat monarchs migratingalong mass of the coastal monarchs compared with those
thecoasthave shorterwnglengthsthanthose migrating collectedinland is thatexcess exertion burnstheirlipids
inland because the larger individuals are more likely to while theyconfront uufav'orable beach winds and cross
getblovwiout toseaandhave more difficultyfl)4ngback- large bodies ofwater, including the numerous bays and
in than do the smaller ones. We are not advocating the sounds along the coast. Gibbs (in Gibbs et al. 2006;
idea that the coastal migrants are a sub-population that Gibbs 2007, pers. comm.) has studied coastal monarch
has been selected for shorterwing lengths. In fact, the migration through Chincoteague in Northern \irginia
likelihood of shorter wings geneticallv evolving is for 14 years (1994-2007) and she has frequently
unlikely because of the random mating that occurs obseived large numbers of monarchsbeingIvlowai outto
among the millions of individuals of the eastern seaandothers strugglingagainstwindsto return to land.
population that takes place in Mexico (Brower f995). She also noted that the butterflies tliat succeeded in
196 Journalofthe Leridorterists’ Society
Table3. Fifteen recoveriesin Mexicooftlie2,224monarchstaggedIryL. BrindzaatinlandandcoastalsitesinVirginiaoverfive
years (2001-2()06). Thetagcitiesarethetownsclosesttotlietagginglocations.
Sex TagCode TagCity TagDate ReportDate WinteringColony
Inland
Female ABJ667 Loiton,\7V 12-Sep-Ol 06-Jan-02 El Rosario
Male ABJS35 Lorton,V'A 22-Sep-Ol 26-Feb-02 El Rosario
Female ABJ782 Lorton,\'A 13-Sep-Ol 26-Feh-02 El Rosario
Male ABJ38S Lorton,VA 04-Sep-()l 26-Feb-02 ElRosario
Female ABJ41.5 Lorton,VA 05-Sep-01 20-Feh-02 SierraCliincua
Male ABJ492 Lorton,\A ()fi-Sep-()l 27-Feh-02 SierraChinena
Female ABJ675 Lorton,VA 12-8ep-01 27-Feh-02 SierraChinena
F’einale AB|497 Lorton,VA ()6-Sep-0l 12-Mar-02 El Rosario
Female ABJ484 Lorton,VA 06-Sep-01 24-Mar-03° El Rosario
Female ABJ682 Lorton,VA 12-Sep-Ol 03-Mar-04“ El Rosario
Male ABj.538 Lorton,VA 07-Sep-()l 18-Mar-05‘’ El Rosario
Male ABJ757 Lorton,VA 13-.Sep-01 lS-Mar-05° El Rosario
Male HCM412 VV'oodliridge,VA 03-Sep-Ofi 20-Feb-07 El Rosario
Coastal
Female A11.546 CapeCharles,VA ()2-Oct-01 18-.Vlar-05° El Rosario
Female HCM160 CapeCharles,V^A 03-Oct-01 06-|an-07 El Rosario
“Timespangreaterthan 1 o\'en\interingseasonhecausetagwasfoundandheldbylocal residentsuntilcollectedbyMonarchWatchofficials
retuniing immediately began neetaring. Louise amounts of lipids in migrating monarchs until they
Zemaitis (pers. cfiinm.) has made similarobsemitions in reach Texas, where tliey then accnmnlate large lipid
Cape May. stores. Lipidstores arecriticaltofuel thebutterflies five
Beall (1948) found that many monarchs perished month ovenvintering period in Mexico (Alonso et al.
while attempting to cross Lake Erie duringthe fall and 1997).
he determined that they had a lower lipid content than We hyjrothesize that onr coastal monarchs were
monarchsthatsnnivedthecrossing. Itthereforeseems lighter than the inland monarchs because they did not
reasonable toconcludethat migrants are forcedtoburn have access to sufficient nectar sources and that this is
more lipid while using powered and flapping flight to due to a diminished flora caused by habitat
contend wath the coastal vrinds and flights across water deterioration along the Atlantic coastal migratory
than the tenfold more energy-efficient soaring and corridor. Wdiile the overall nectar abundance may
gliding that is common in the less windy inland always have been less along the coast than inland, as
environment (Schmidt-Koenig 1985; Masters et al. nowdiscussed, this is doubtful.
1988; Da\4s & Garland 2004; Broweretal. 2006). The coastal habitats. The dynamic ecological
Are the diminished neetar resources and low interrelationships of coastal habitats are described in
lipid levels due to human encroachment? As Frid & Evans (1995). They include long ribbons of
implied by onr having caught most ofonrbutterflies at barrier and sea islands that over geological time
flowers, monarchs frecpiently interrupt their fall developed a series ofveiy different habitats extending
migration to drink nectar. Sugar that is contained in from theseato inland (Christensen 1988). Thehabitats
nectaris convertedto lipidthatthe butteidlies store and includethe sandybeaches, coastalprairies, primaiyand
use to fuel their flight and other activities. In a recent secondaiy sand dunes and wetland swales behind the
study, Brower et al. (2006) found only moderate dimes (Silberhorn 1999). Furtherinland are saline and
Volume 62, Number 4 197
Table 4. Results ofANOVA model explaining variation in restored habitat. To what extent have humans
winglength ofmigrating monarcli butterilies. The dataforthe diminished this environment?
2004yearwere not includedin tlle analysis. All two-wayinter- Human encroachment. Hitman exploitation of the
actionswere initiallyincluded in the model butwere removeil
when foundnotsignificant. valuable economic resources offered by the dynamic
coastal ecosystems andits severe impactontheirnatural
Independent df MS F P features is documented in numerous studies (Turneret
Site 1 17 4.0 0.046 al. 1998; Doody 2002; Ray & McCormick-Ray 2003;
Year 3 46 10.5 <l).()01 Bnrronghs & Tebhins 2005; Feaginetal. 2005; Forman
et al. 2005; Verhoeven et al. 2006; Martinez & PsuH
Sex 1 15 3.5 0.064 2007). The construction of buildings, dikes, parking
Error 611 4 lots, roads, etc. often stpieezes the land against the
Total 616 ocean and blocks the natural inland sand movement.
Sea currents then either wash the sandy beaches, the
AfrceesohrwdaitnegretsotiiDaeil'iaecs,onlragtoo&ns,Desloaucnodnsrtan(d19e8o1a)s,taltlifiosrevsetisy. prreaminriaenstsanwditthheed.ixtmeenssivaewlayy,diormirneidsuhceed tfhloermas.to mIetries
dynamic ecosystem complex has persisted for tlie last
estimated that 350,000 structures in the United States
9000 years, about as long as the current monarch
are located within 500 feet oftlie shorelines and nearly
butterfly migration is thought to have existed (Brower half of all coastal wetlands have been destroyed since
1995). Even though the various communities within
pre-Columbian times (Beatley ct al. 2002). Dredging
this environmental can he complex and harsh (Barbour
& Christensen 1993), they have specialized, productive adentderdiiotrcahtiendg imnutchhe fciorsatsthaallfhoafbitthaet 2(0Hthumcpehnrtneiyy aalnsdo
and diverse floras (Barbour 1992; Tiner 1987, 1993;
Packham & Willis 1997; Silherhorn 1999), These Rockefeller 1968), Although passage of the 1972
Wetlands Act helped mitigate tlie losses, Beatleyet al.
iuclude numerous annual and perennial plants that
(2002, p. 283) tell ns: "Alarm bells are ringing
seiwe as nectar sources for the monarch butterfly
eveiywhere as our coastal eiiviroiiment endures
migratingthrough the complexof habitats each fall. unabated development pressures and environmental
According to Bird (1985), coastal erosion through
degradation".
rising sea level has impacted about 70% of the planet's
Another negative anthropogenic impact is the
sandy beach environments including those along the
spraying of herbicides, including gly^ihosate
North American Atlantic coast. Rising sea level causes
("Roundup", Monsanto, Inc., see Anon. 2005) and
the beach, coastal prairie and dune habitats to erode, iniazapyr ("Habitat", BASF Inc., see Anon. 2007b), to
but, with slow risingconditions, the habitats reestablish
control marsh reed grass, Phragmite.s australis (Cav.)
further inland. They then undergo ecological
Trill, ex Steud. (Poaceae). These biocides, either
succession anti the flora physically stabilizes the
directlvorthrough inadvertentwdiid driftwlien applied
Table 5, Re,snlts ofANOVA model explaining variation in by helicopters, can kill the nectar sources adjacent to
wet ma.ss of migrating monarcl] butterflies. Tlie data for the the marshes. For example, spraying herbiciiles was a
2004yearwerenotinclntledin theanalysis. Theinteraetionsof major issue in Cape May in 2005 (Fichter 2005) and in
wSietree°SreexmaonvdedYewahre°nSefxowuenrdenointitsiiaglnliyfiicnacnlt.uded in tlie model lint the Chincoteague National Wildlife Refuge iii 2006.
According to Denise Gibbs (pers. comm.), helicopter
Independent df MS F p spraying on Chincoteague is forbidden if t—he wind
exceeds 5 mph. However, on 2 October 2006 peak
Site 1 8280 1.9 0.164 — a
monarch butterfly migration day the spraying was
Year 3 36516 8.6 <0.001 continued with a 15 mph wind, drifting "Habitat" for at
Sex 1 18595 4.4 0.037 least a half a mile across a main Soliclago sempervirens
nectaring area. Yet other impacts are e.xemplified by
WingLength 1 778160 182.5 <0.0()1 helicopter spraying ofmalathion (see Anon. 2006) and
Sex'WingLengtl1 1 14502 3.4 0.066 by truck misting with the pyrethroid derivative
resmethrin, ("Scourge", Aventis Environniental Science,
Site"’WingLength 1 12449 2.9 0.088 see Anon. 2007c) formosquitocontrol bythe Cape May
Site'Year 3 24216 5.7 0.001 County Mosquito Commission. A related synthetic
Error 602 4263 pyrethroid ("Perniethrin") has been found to kill
monarchs in lioth larval and adult stages and has long
Total 613 term effects on the butterflies (Oberhauserct al. 2006).
198 Journalofthe LEPiDOPXERrsTS’ Societa'
The extent to which these various physical and migration progresses from Maine to Elorida.
chemical impacts have diminished the quantity and To test onr habitat deterioration hypothesis,
qualityofthe nectarsources in the coastal enwronment comparative measurements of the amount of nectar
has not been quantified, but the losses have almost imbibed by monarchs (methods in Brower et al. in
certainly affected the lipid and hydration dynamics of prep.) collected at inland and the coastal sites could be
fall migrant monarch butterflies, as well as the nectar made. Currently, there are hundreds of citizen-
re(|iiirements ofother animals living in and using tins scientists (Monarch Watch 2006; Prysby & Oberhauser
migratoiycorridor(Nabhan 2004; Brower& Pvle2004). 2004) who study, capture, tag and release monarchs
Inland habitats. In contrast to the natural and eachyear. Direct measurements ofwdnglength andwet
anthropogenic hazards to monarchs flying along the mass, as done inthis studywithoutkillingthe individual
coast, flight over the far more extensive inland routes monarchs,wouldhelpbuildlongterm comparativedata
wdth diverse and varied nectar resources may not be as sets. However, more accurate measurements of both
stressful. Inland environments are also subject to less lipid and water contents of the inland and coastal
intense wind and, until recently, I'oadsides and monarchs are needed. Wet mass is the sum of the
agricultural fields provided extensive areas with w^ater, lipid and the lean body mass. Consequently, the
wildflowers. Unfortunately, the ever-increasing use of coi'relationbetweenwet massofthewholebutterflyand
herbicides on roadsides, and, in conjunction with the the contained lipid mass is weak and confounds the
repeated spraying of corn and soybean crops that are masses ofwater and lipid. In order to measure both
geneticallyengineered to be resistant to the herbicides, accurately, the moiiarchs must be killed by freezing,
areeliminatinghuge areas offloral resources (Broweret w'eighed, dehydrated, weighed again, and then their
al. 2006). lipids extracted and w^eighed (Brower et al. in prep.).
Alternative hypotheses and future research. An Citizen-scientists conld collect and freeze monarch
alternative hvpothesis to account for the smaller and samples and have professionals cany out the lipid and
lightercoastal monarchs is thatfeweroftheirlaiwaehad waterdeterminations in aw^ell-coordinated project.
the opportunity to feed on Asclepias sifriaca L.
Acknowledgements
(Asciepiadaceae), the major food plant (Malcolm et al.
19S9) ofthe monarch's easternpopulation andis known WethankthefollowingforfieldassistanceinVirginia: Sharna
Tolfree, Randy Emmitt, David Haynes, and Elizabeth
to be nutritionally superior to Asclepias tuberosa L. Townsend,allsupportedbytheCoastalVirginiaWildlifeObser-
(Erickson 1973). The latter milkAveed is widely \atorv. Logisticsupportwasalsoprovidedto BrindzabytheOc-
distributed along the Atlantic coast (Woodson 1954), coquan BayNationalWildlife Refuge, Eastern ShoreofVirginia
National Wildlife Refuge, Mason Neck State Park, Kiptopeke
and it is possible that more ofthe coastal migrants had State Park, and the Chesapeake Bay Bridge-Tunnel. We are
fed on it and ended up as smaller indiwduals. Thin grateful to Linda Fink, Richard Walton, Louise Zeniaitis and
layer chromatography analyses (Malcolm et al. 1989) two reviewers for critical comments on the manuscript, to
Denise Gibbs forsharinginformation on the migration through
could determine iftlie food plants eaten by the lanae Chincoteague, VA., andto Peter Raven foridentifyingscientists
differed among the larger and smaller inclMdual familiarwith the Atlantic coastal flora, including Michael Bar-
butterflies. However, this explanation seems unlikely Jbaonure,tSJtaemveesn.MoWrerisa,ppGreecrirayteMotoheree,noGremoorugseeYfaftosrktiseov)f'Ocrh;leaynTdayt-o
because, as implied above, the majority of coastal lor in coordinating the Monarch Watch tagging program, for
monarchs probably fed on A. sifriaca plants growing purchase ofrecoveredtagsin Mexico andfordisseminatingre-
inlandbeforebeingwind-drifted to the coast. capturedata. Robert Dudley, thoughskepticalofourwdndloss
hypothesis,providedv'aluablecommentaiyandinsights. Finan-
Another possibility is that the smaller and lighter cial supportwas providedovertheyears byTheWildlife Con-
monarchs were less able than the larger and heavier seiwation Society, Paul and Kathy Reinhold, The October Hill
ones to resist winds that blew them towards the coast. Foundation, and by National Science Foundation grant DEB-
0415340toSweetBriarCollegewith Lincoln BrowerandLinda
This is consistent with Beall's (1948) finding that the Finkasprincipaliiwestigators. AKDwassupportedbytheD.B.
monarchs that drowned crossing Lake Erie were both Warnell School ofForestry and Natural Resources at the Uni-
smallerandlighterthan ones hecollectedin roostsboth versityofGeorgiaduringthewritingofthis manuscript.
north and south of the lake collections. Another Literature Cited
possibility is that the monarchs with lower mass were
Alexander, D. E. 2002. Nature'sflyers.TheJohns HopkinsUniver-
more fuel and/or water stressed and therefore siyPress, Baltimore, Maryland.
accumulated on the coast to nectar, while the heavier Alonso-Mejia, a., E. Rendon-Salinas, E. Montesinos-Patino, &
ones kept migratingsouth. Itisimportanttoremember L. P. Brower. 1997. Useoflipidreserv'esbymonarchbuttenflies
overwinteringinMexico: implicationsforconservation. Ecologi-
that our samples were gathered in a veiy limited calApplications7:934-947.
latitudinal transect. Much light could be shed on the Anon.200.5. Monsantoimagine: BackgrounderhistoryofMonsanto's
questions byanalyzingcollections alongthe coast as the glyphosate her'bicides, June 2005, http://vvAvw.nronsanto.eorn/