The causes and biogeographical significance of species rediscovery

Abstract

Abstract. The rediscovery of a species that was putatively considered to be extinct can provide valuable
data to test biogeographical hypotheses about population decline and range collapse. Moreover, such
rediscoveries often generate much‐needed publicity and additional funds for the conservation of rare
species and habitats. However, like extinction, rediscovery is challenging to define. In this perspective
we argue that the ‘loss’ of a species and its subsequent rediscovery can be understood in terms of the
interplay among four socio‐ecological factors: (1) the state of knowledge of species loss and rediscovery;
(2) the presence of people and/or organizations with the interest, motivation, resources, skills and technology
to find target species; (3) the accessibility of the areas, habitats or sites where the species are
thought to survive; and (4) the ease with which a species can be located when it is present within a habitat.
Thus, species are ‘lost’ from scientific knowledge for different reasons and, consequently, not all
rediscoveries are equally significant for biogeographical research or conservation. Indeed, rediscoveries
of species that underwent a well documented decline and disappearance – and are therefore of greatest
potential importance for both conservation and biogeographical research – appear to be poorly represented
in the literature compared to rediscovered species that were only known from a handful of museum
specimens. Thus, carefully distinguishing between the causes of temporal gaps in zoological records
is essential for improving the utility of rediscovery data for biogeographical research and conservation
practice.

Full text

Introduction
Rediscoveriesofputativelyextinctspeciesareof
greatpotentialinteresttobothconservationists
andbiogeographers(Crowley2011).Forthefor‐
mer,‘rediscovery’canbeaconsiderableconserva‐
tionpolicyandpublicityasset(LadleandJepson
2008,Ladleetal.2009)–astestifiedbyrecent
globalinitiatives:in2009BirdLifeInternational
launcheda“globalbidtotrytoconfirmthecon‐
tinuedexistenceof47speciesofbirdthathave
notbeenseenforupto184years”(BirdLifeInter‐
national2009).ThefollowingyearConservation
Internationallaunchedits“SearchforlostFrogs”
whichinvolvesadedicatedcampaignandexpedi‐
tionsto18countriesseekingtolocate40species
notseenforadecadeormore(ConservationIn‐
ternational2010)–atthetimeofwriting12spe‐
cieshavebeenrediscovered.Moreover,sincere‐
discoveredspeciesaretypicallyexceedinglyrare
andgeographicallylocalized,newknowledgeon
populationstatusanddistributionsupportseffec‐
tiveconservationinterventions.Finally,rediscov‐
eriesremoveuncertaintyfromextinctionriskas‐
sessments;aconfirmednewrecordmovesthe
speciesfrom‘extinct’or‘probablyextinct’and
intoanIUCNthreat(ordatadeficient)category.
Forbiogeographers,speciesrediscoveryhasboth
apracticalandconceptualsignificance.Fromthe
ISSN1948‐6596
perspective
Thecausesandbiogeographicalsignificance
ofspecies’rediscovery
RichardJ.Ladle1,2,*,PaulJepson2,AnaC.M.Malhado1,
SteveJennings3andMaanBarua2
1.InstituteofBiologicalandHealthSciences,FederalUniversityofAlagoas,Maceió,AL,Brazil.2.School
ofGeographyandtheEnvironment,UniversityofOxford,SouthParksRoad,Oxford,OX13QY,United
Kingdom.3.OxfamGB,OxfamHouse,JohnSmithDrive,Oxford,UnitedKingdom.
*Authorforcorrespondence:DrRichardJ.Ladle,InstituteofBiologicalandHealthSciences,FederalUni‐
versityofAlagoas,PraçaAfrânioJorge,s/n,Prado,Maceió,AL,Brazil,57010‐020.
e‐mail:richard.ladle@ouce.ox.ac.uk;http://www.geog.ox.ac.uk/staff/rladle.html
Abstract.Therediscoveryofaspeciesthatwasputativelyconsideredtobeextinctcanprovidevaluable
datatotestbiogeographicalhypothesesaboutpopulationdeclineandrangecollapse.Moreover,such
rediscoveriesoftengeneratemuch‐neededpublicityandadditionalfundsfortheconservationofrare
speciesandhabitats.However,likeextinction,rediscoveryischallengingtodefine.Inthisperspective
wearguethatthe‘loss’ofaspeciesanditssubsequentrediscoverycanbeunderstoodintermsofthe
interplayamongfoursocio‐ecologicalfactors:(1)thestateofknowledgeofspecieslossandrediscovery;
(2)thepresenceofpeopleand/ororganizationswiththeinterest,motivation,resources,skillsandtech‐
nologytofindtargetspecies;(3)theaccessibilityoftheareas,habitatsorsiteswherethespeciesare
thoughttosurvive;and(4)theeasewithwhichaspeciescanbelocatedwhenitispresentwithinahabi‐
tat.Thus,speciesare‘lost’fromscientificknowledgefordifferentreasonsand,consequently,notall
rediscoveriesareequallysignificantforbiogeographicalresearchorconservation.Indeed,rediscoveries
ofspeciesthatunderwentawelldocumenteddeclineanddisappearance–andarethereforeofgreatest
potentialimportanceforbothconservationandbiogeographicalresearch–appeartobepoorlyrepre‐
sentedintheliteraturecomparedtorediscoveredspeciesthatwereonlyknownfromahandfulofmu‐
seumspecimens.Thus,carefullydistinguishingbetweenthecausesoftemporalgapsinzoologicalre‐
cordsisessentialforimprovingtheutilityofrediscoverydataforbiogeographicalresearchandconser‐
vationpractice.
Keywords:extinction,rangecollapse,rarity,criticallyendangered,monitoring
opinionandperspectives
104©2011theauthors;journalcompilation©2011TheInternationalBiogeographySociety—frontiersofbiogeography3.3,2011

RichardJ.Ladleetal.
practicalperspective,therediscoveryofaspecies
thathasgoneunrecordedforalongperiodof
timeimprovesgeographicalknowledgeabout
someoftheworld’srarestspecies,helpingtoad‐
dresstheWallaceanshortfall–theinadequacyof
ourknowledgeofthegeographicaldistributionsof
species(Lomolinoetal.2006,Riddleetal.2011).
Theshortfallcanoftenbeextreme,withaspecies
knownfromjustoneorafewmuseumspecimens
collecteddecadesorevencenturiesearlier.These
speciesaresometimesincorrectlyassumedorde‐
claredextinct,aphenomenonwhichLadleand
Jepson(2008)refertoasaWallaceanextinction.
Aswediscusslater,theseextremeexamplesof
theWallaceanshortfallareamongstthemostfre‐
quentlyrediscoveredspecies.
Morerecently,biogeographershavestarted
touseinformationonspeciesrediscoveriestotest
theoriesofpopulationdeclineandrangecollapse
underanthropogenicdisturbance(Fisher2011a,b;
FisherandBlomberg2011).Theunderlyingideais
bothsimpleandelegant:thelocationofaredis‐
coveredspeciesrelativetoitshistoricalrangere‐
flectsthepatternofrangecollapse.Thus,ifan‐
thropogenicpressures(e.g.unsustainableexploi‐
tation)arestrongestattheperiphery(Channel
andLomolino2000)therediscoverywillmost
likelybemadenearthecentreofthehistoric
range.DianaFisher’s(2011a)studyof67species
ofrediscoveredmammalsfoundanumberofclear
trends,althoughthesetendedtobedependent
upontheecologyofthespecies.Forexample,one
ofthestrongestpatternsobservedwasthatredis‐
coveriesweregenerallymadeathigherelevations
thantheoriginalrecord(excludingmountain‐top
andcoastallyrestrictedspecies).Thisprovides
somesupportforthehypothesisthathigherele‐
vationscansometimesprovideecologicalrefugia
(TownsandDaugherty 1994)andfitswiththefre‐
quentlyobservedpatternofhabitatdestruction
andpopulationextinctionprogressingfromlowto
highaltitudes(Triantisetal.2010).
However,likeextinction,rediscoveryis
challengingtodefine.Thisshouldnotbesurpris‐
ingsincerediscoveryandextinctionareconceptu‐
allyintertwined;extinctionisthepermanentab‐
senceofcurrentandfuturerecordswhileredis‐
coveryreflectsthetemporaryabsenceofsuch
records.Moreover,rediscoveryistheproofre‐
quiredtorefuteahypothesisofextinction.Given
thecloseconceptuallinkagebetweenthecon‐
ceptsofrediscoveryandextinctionitisinteresting
that,untilrecently,therehavebeensofewstud‐
ieslinkingpatternsofrediscoverytocontempo‐
rarytheoriesofpopulationdeclineandextinction.
Oneimpedimenttosuchresearchisthelackofa
systematicapproachtospeciesrediscoveriesthat
allowscientiststoidentifycasesofrediscovery
thathavebiogeographicalorconservationsignifi‐
cance,andwhichcanbesubjecttomeaningful
analysis.Here,weproposeaconceptualframe‐
workforunderstandingandanalyzingspeciesre‐
discovery,basedonthesocial,institutionaland
ecologicalfactorsthatcreatedthetemporalgapin
occurrencedata.Webelievethatformalizingthe
conceptofrediscoveryinthiswayhasthepoten‐
tialtocreatenewmeasuresofthestateofknowl‐
edgeoftheworld’srarestspecies,provideaquan‐
tifiablemetrictosupportexistingendangerment
categorizations,andwouldhelptomaintainthe
cultureofbiogeographicalexplorationthatcon‐
tributestothedatasetsthatunderpinglobalcon‐
servationtarget‐setting,advocacyandmonitoring.

Conceptualframework
The‘loss’ofaspeciesanditssubsequentrediscov‐
erycanbeconceptualizedasaresultoftheinter‐
playamongfoursocio‐ecologicalaspectsofredis‐
covery(schematicallyillustratedinFigure1):(1)
thestateofknowledgeofspecieslossandredis‐
covery;(2)thepresenceofpeopleand/ororgani‐
zationswiththeinterest,motivation,resources,
skillsandtechnologytofindtargetspecies;(3)the
accessibilityoftheareas,habitatsorsiteswhere
thespeciesarethoughttosurvive;and(4)the
easewithwhichaspeciescanbelocatedwhenit
ispresentwithinahabitat.Itshouldbenotedthat
althoughthesefactorspotentiallyapplytoall
‘lost’taxa,owingtoissuesofhistoricaldataqual‐
ity,fundingandthecultureofscientificexplora‐
tion,rediscoveryresearchhasfocusedalmostex‐
clusivelyonherptiles,birdsandmammals(cf.
Scheffersetal.2011).

105frontiersofbiogeography3.3,2011—©2011theauthors;journalcompilation©2011TheInternationalBiogeographySociety

Knowledgeof‘lost’species
Enormousadvanceshavebeenmadeoverthelast
40yearsinenumeratingwhichspeciesareappar‐
ently‘lost’.Forexample,BirdLifeInternationalhas
madesignificantinvestmentsincompilingnew
andauthoritativeassessmentsofthreatenedspe‐
ciesusinginformationfromavarietyofsources
includingamateuranduniversity‐ledresearchex‐
peditionsandmajorreviewsofexistingmuseum
specimens.Inparticular,fromthemid1980stwo
majorregionalRedListreviewswerecompiledfor
theAmericas(Collaretal.1992)andAsia(Collar
etal.2001),thefindingsofwhichwerethenfed
backtotheBirdLifenetworkofpioneeringprofes‐
sionalandamateurornithologists(Tobiasetal.
2006,Butchart2007).
Theknowledgeofwhatis‘lost’iscompli‐
cated,asrediscoveriescanlogicallybesplitinto
fourcategoriesthatreflectdifferentdegreesof
uncertainty(andauthority)aboutthecontinued
existenceofatargetspecies(Table1).Anaddi‐
tionalcategorycouldpotentiallybeaddedtothis
typologytoaccountforcaseswhereanunre‐
cordedsub‐speciesiselevatedtofullspecies
status.Forexample,theSangiheShrike‐thrush
(Colluricinclasanghirensis)wasrediscoveredin
1985butitsstatusasafullspecieswasonlyestab‐
lishedin1999(RozendaalandLambert1999).
Changesintaxonomicstatusmayhaveprofound
impactsonsurveyeffort:accordingtoRasmussen
etal.(2000),thedemotionoftheSangiheWhite‐
eye(Zosteropsnehrkorni)tosub‐specificstatusby
Stresemann(1931)hadtheeffectofmakingthe
speciesof“onlymarginal,regionalinterest”and
asaconsequence“formanyyears[it]received
littleattention”(p.69).
Fromtheperspectiveofinvestigatingrange
changes,confoundingdifferentcategoriesofre‐
discoverycouldseriouslyinfluenceresearchfind‐
ings.Forexample,wemightexpectthatallother
thingsbeingequal,specieswhosehabitatorrange
hasnotbeensurveyedforasignificantperiodof
timeandforwhichtherearenostrongreasonsto
assumehavebecomeextinct(Table1,category4),
areaslikelytoberediscoveredattheedgeorcen‐
treoftheirhistoricrangeasarebetter‐known
species.Moreover,allfourcategoriesofrediscov‐
erymaycontainspeciesthatwereonlyknown
fromasmallnumberofmuseumspecimens–the
rediscoveryofwhichmaytellsusmoreaboutthe
historyofbiogeographicalexplorationthanthe
ecologyofdeclineandextinction.Indeed,Schef‐
fersetal.(2011)foundthatthemajorityofre‐
centlyclaimedamphibian,birdandmammalre‐
discoveriesrepresentfirstdocumentationssince
theiroriginalscientificdescription.Itshouldalso
benotedthatsuchrarespeciesmayhavere‐
mainedunrecordedbecauseofintrinsicbiological
characteristics(e.g.nocturnalhabits,cryptic
colouration,etc.)ratherthanalackofsampling
effortandthatthesefactorsneedtobecarefully
untangledinanyanalysisofpatternsofrediscov‐
ery(seeMcCarthy2008;FisherandBlomberg
2011).
rediscoveriesinbiogeography
Figure1.Thefourmajordimensions
ofspeciesrediscovery(seetext).
106©2011theauthors;journalcompilation©2011TheInternationalBiogeographySociety—frontiersofbiogeography3.3,2011

RichardJ.Ladleetal.
Perhapsthemostimportanttypeofredis‐
coveryforconservationiswhereapreviouslywell
knownspeciesundergoesapopulationdecline,is
lostfrombiogeographicalknowledge,andisthen
rediscovered.ApossibleexampleistheAustralian
PygmyBlue‐tongueLizardTiliquaadelaidensis.
Thisrathersecretivelizardwasrelativelywell
knownuptoitsdisappearancein1959;itsredis‐
coveryin1992(inthestomachofasnake)con‐
firmedthatthespeciesnowhas“adramatically
reducedgeographicalrange”(MilneandBull
2000,p.296).TherediscoveryoftheIvory‐billed
Woodpecker(Campephilusprincipalis)(Fitzpatrick
etal.2005)wouldbeanevenbetterexample,ex‐
ceptthatthisrediscoveryisincreasinglylooking
likeacaseofmistakenidentity(Dalton2005,
2010,Stokstad2007).Theapparentscarcityof
suchrediscoveries(cf.Scheffersetal.2011)
stronglysuggeststhataspeciesthatundergoesa
welldocumenteddeclineanddisappearanceis
likelytobeextinct.However,formallytestingthis
hypothesiswouldrequiregoodinformationon
populationtrendsofrediscoveredspeciespriorto
theiroriginaldisappearance–datathatrarelyex‐
istforoldercasesofspeciesloss.
Afinalaspectoftheknowledgeneededto
find‘lost’speciesisthereliabilityofbiogeographic
informationonwheretosearchforthespecies.
Thus,theBlack‐hoodedAntwren(Formicivora
erythronotos)wasknownonlyfroma19thCentury
typespecimen,forwhichthetypelocalitywas
probablyincorrect,andwhichwasalsoputinthe
wronggenus.Balchon(2007)suggeststhatthis
ledtoresearchers“lookinginthewrongplace,for
thewrongsortofbirdandlisteningforinappropri‐
atevocalizations”.Thus,‘lost’speciescansome‐
timesturnupthousandsofkilometresawayfrom
wheretheywerelastseen,orincompletelydiffer‐
enthabitats.Forexample,theLarge‐billedReed
Warbler(Acrocephalusorinus)waspreviously
knownfromjustasinglespecimencollectedin
1867intheSutlejValley,HimachalPradesh,India.
However,alivingspecimenwastrappedinMarch
2006atLaemPhakBia,PhatchaburiProvince,
south‐westThailand,over3000kmfromthetype
locality(Roundetal.2007).Therenewedinterest
inthisspeciesledtotheunearthingoftennew
museumspecimens(Svenssonetal.2008)and,
shortlyafterwards,tothediscoveryofabreeding
populationinnorth‐eastAfghanistan(Timminset
al.2010).

Institutional,scientificandtechnicalcapacity
Evenwhenaspeciesisidentifiedaspossiblystill
extant,theinstitutionalandtechnicalcapacityto
finditmaynotexist.Suchcapacity,ataglobal
Table1.Acrudetypologyofspeciesrediscoverybasedondecreasinglevelofcertaintythattherediscoveredspecies
wasextinct.
TypeRediscoveryof…Example
1.aspeciesdeclaredextinctbyanauthori‐
tativesource
ThePohnpeiStarling(Aplonispelzelni)wasdeclared
extinctbytheIUCN(1990)andrediscoveredin1995
(Buden1996)
2.aspeciesconsideredprobablyextinctby
anauthoritativesource
TheSaoTomeGrosbeak(Neospizaconcolor)was
describedasprobablyextinctbyGreenway(1967)
andrediscoveredin1991(Sergeantetal.1992)
3.aspeciesbelievedtobestillextantbut
forwhichsubstantivesearchesoverdec‐
adeshavedrawnablank.
AccordingtotheNGOBirdLifeInternationalthe
MadagascarSerpentEagle(Eutriorchisastur)was
notdefinitelyrecordedbetween1930and1993de‐
spiteconsiderablesearch‐effortwithinitshabitat.
4.aspecieswhosehabitatorrangehadnot
beensurveyedforasignificantperiodof
time,butforwhichthereisnorealrea‐
sontoassumehasbecomeextinct
TheChestnut‐belliedFlowerpiercer(Diglossaglorio‐
sissima)wasunrecordedfor38years:since2003it
hasbeenrecordedfromthreelocations(Tobiaset
al.2006)
107frontiersofbiogeography3.3,2011—©2011theauthors;journalcompilation©2011TheInternationalBiogeographySociety

level,hasvariedconsiderablyovertimeandspace
inresponsetovariousculturalandecologicalfac‐
tors.Mostnotably,themainstreamingofbiodiver‐
sityintointernationaldevelopmentfollowingthe
1992EarthSummitcreatedmanynewsourcesof
fundsandemploymentopportunitiesforscientists
inless‐developedcountries.Withrespecttobirds,
thisincreaseinlocalcapacitycoincidedwiththe
creationofBirdLifeInternationalin1993.BirdLife
emergedfromtheInternationalCouncilforBird
Preservation(foundedin1922)whenitsleaders
devisedthecompellingpropositionofformingan
internationalpartnership,underasinglename,
withsmaller,national,bird‐orientatedconserva‐
tionorganizations(JepsonandLadle2010).More
generally,increasedfundingofexpeditionsbyin‐
ternationalNGOshasprobablybeenthedriving
forcebehindtheincreasingfrequencyofrediscov‐
eriesofvarioustaxa(Scheffersetal.2011).
Othertrendswithinscienceandconserva‐
tionalsohelpdeterminethecapacityandmotiva‐
tionthatenablesrediscoveries,especiallythein‐
troductionofnewtechnology.Forexample,ad‐
vancesinmolecularbiologyhavemadeitmuch
easiertogeneticallycomparepreservedtype
specimensinmuseumswithcontemporarymate‐
rialcollecteddirectlyoracquiredfromhuntersor
fromruralmarkets.Thishasopenedthewayfor
completelynewwaysofrediscoveringlostspe‐
cies,whereafragmentofhairorafaecalsample
maybesufficienttoprovethecontinuingexis‐
tenceofaspeciesthathasstillnotbeenphysically
observed.
Anexcellentexampleofsuchatechnology‐
aideddiscoveryisprovidedbyPitraetal.(2006),
whorecentlyannouncedthecontinuingexistence
ofthegiantsableantelope(Hippotragusniger
variani),asub‐speciesuniquetoAngolathatwas
fearedextinctafteralmostthreedecadesofcivil
war.TheycomparedthemitochondrialDNAse‐
quencesderivedfromoldmuseumspecimens
withsamplesextractedfromdungsamplesre‐
centlycollectedinthefield.Suchremotelycol‐
lectedDNAevidencecanalsobeusedtodiscount
presumeddiscoveriesorrediscoveries.Forexam‐
ple,Hennacheetal.(2003)usedarangeoftech‐
niques,includingcaptivehybridizationexperi‐
mentsandanalysisofmitochondrialDNAandmi‐
crosatellites,toconclusivelydemonstratethehy‐
bridoriginoftheimperialpheasant(Lophuraim‐
perialis).Thismysteriousbirdhadfirstbeencap‐
turedin1924whenasinglepairhadbeenshipped
totheprivateaviaryofJeanDelacourinFrance
andwasnotseenagainuntilonewastrappedin
1990(Hennacheetal.2003).
Itisnotonlyadvancesinmolecularbiology
thatarefacilitatingrediscoveries.Thereadyavail‐
abilityofsophisticatedaudiovisualequipmenthas
beenespeciallyimportantintheevolutionofbird
surveying.Twosuchtechnologicaladvances,the
increasedavailabilityoflessexpensivesound‐
recordingandplaybackequipmentinthelate
1990sandthemorerecentinternet‐basedbird‐
soundarchives,havedramaticallyincreasedthe
capacityofbothamateursandprofessionalsto
locateandidentifyrareandcrypticbirdspecies.
Moreover,advancesinthequalityofcamerasand
lenses,especiallydigitalcamerasandvideore‐
corders,havealsobeenimportantindocumenting
andprovidingdefinitiveproofoftheexistenceof
veryrarespecies.Forexample,theNewZealand
StormPetrel(Pealeornismaoriana)wasidentified
fromthedetailsonadigitalimagetakenin2003
(Stephensonetal.2008).Ithadpreviouslybeen
knownonlyfromputativefossilmaterial,and
fromthreespecimenscollectedinthe19thCen‐
tury,150yearsbeforeitsrediscovery.

Accessibility
Evenifaspeciesisextantandpotentialhabitats
havebeenlocated,thespeciesmaynotbefound.
Accesstosuitablehabitatmaybelimitedbecause
ofpoliticalinstability/restrictions,orsimplythe
remotenessofpotentialsites.Althoughintheera
ofcheapinternationalairtravelthisisarguably
lessimportant,itmayhaveplayedacriticalrolein
restrictingtheintensityofsurveysandtherefore
therateofrediscoveriesinmanypartsofthe
globe.Examplesofrediscoveriesthatwereproba‐
blydelayed,andpossiblyevencaused,bypolitical
instabilityincludethatoftheLarge‐billedReed
WarblerinAfghanistan(seeabove)andthe
GabelaHelmet‐shrike(Prionopsgabela),rediscov‐
eredin2003inAngola(Ryanetal2004).
rediscoveriesinbiogeography
108©2011theauthors;journalcompilation©2011TheInternationalBiogeographySociety—frontiersofbiogeography3.3,2011

RichardJ.Ladleetal.
Acloselyrelatedfactorisalackofcommu‐
nicationwithremoteandisolatedruralcommuni‐
tieswhomayalreadyhaveknowledgeofthecon‐
tinuedexistenceofaputativelyextinctspecies,or
ofaspeciesnewtoscience.Thus,aproductive
routetoincreasingrediscoveries(andnewspecies
discoveries)mightbethroughbettercommunica‐
tionwithremotetribesandcommunitieswhose
knowledgeoflocalbiodiversitymayextendcon‐
siderablybeyondthatofconservationists.How‐
ever,FisherandBlomberg(2011)foundthathu‐
manpopulationoverlapdidnotpredictrediscov‐
eryrateinmammals,possiblybecauseexpedi‐
tionsandsurveysmayintentionallyfocusonmore
remoteareas.

Ecologicalfactors
Thefinalaspectofrediscoveryistheecological
characteristicsoftheputativelyextinctspecies
thatmaymakeverificationofitscontinuedexis‐
tenceproblematic.Forexample,ifthespeciesis
veryrareand/ordispersed,thenitmaybedifficult
tolocateanindividual/populationwithinanarea
ofpotentiallysuitablehabitat.Evenifthesurvey
teamisinthesameareaasthetargetspecies,it
maystillnotbeencounteredbecauseofpheno‐
typicandecologicaltraits(e.g.crypticcoloration,
lackofvocalizations,skulkingbehaviour,etc.)that
reducetheprobabilityofdetection(Schefferset
al.2011).However,theevidenceforthiseffectis
variable:FisherandBlomberg(2011)foundthatin
mammalsmanyecologicalcharacteristicssuchas
crypticcolorationandarborealandnocturnalbe‐
haviourwerenotsignificantlyassociatedwithre‐
discovery–althoughsmallerrediscoveredmam‐
malshadbeenmissingforlongerperiodsoftime
(Fisher2011b).
Apossibleexampleofecologydrivingthe
lackofrecordsistheNightParrot,aspeciesthatis
knownfrom23specimensandmanysightingsof
varyingreliabilityfromawidegeographicareaof
inlandAustralia(McDougalletal2009).From
whatlittleinformationexists,theNightParrotis
crepuscularornocturnal,cryptic,andwhenap‐
proachedwillonlyflushatclosequarters,thenfly
lowovershortdistancesbeforeplungingbackinto
cover(ForshawandCooper2002).Perhapsunsur‐
prisingly,between1912and1990therewereno
recordsoftheNightParrotuntilonewashitby
traffic(Bolesetal.1994).

Rediscoveriesreconsidered
Giventheverylooseusageoftheterm
‘rediscovery’andthevaryingfactors,socialand
ecological,thatcontributetorediscoveries,both
biogeographyandconservationmaybenefitfrom
adoptingastricterpolicyofusage.Onestrategy
wouldbetostrictlyconfinetheterm‘rediscovery’
tospeciescategorizedasextinctintheIUCNsys‐
tem(Maceetal.2008)oras‘possiblyextinct’,or
‘lost’byauthoritativesources(Table1,categories
1,2and3).Itshouldbenotedthatmanyspecies
thatareconsideredpossiblyextinctarelistedas
“criticallyendangered”intheIUCNsystem.For
example,Fisher(2011a)restrictsheranalysisto
rediscoveredmammalspeciesthathadbeenpre‐
viouslyreportedasgloballyextinctorpossiblyex‐
tinct.Itshouldbenoted,however,thatthisap‐
proachwillnotcompletelyeliminateallthecases
ofspeciesthataremissingthroughlowlevelsof
surveying.
Analternativestrategycouldbetoclassify
rediscoverypurelyintermsofthelengthoftime
withoutaformalrecord.Ifthiswereadopted,the
onlyissuewouldbeanappropriatetimeframefor
agiventaxon.Forexample,DeRolandetal.
(2007)feltjustifiedinclaimingthe‘rediscovery’of
theMadagascarPochard(Athyainnotata)just15
yearsafterthelastconfirmedsighting–conceiva‐
blythesameindividual.
Usingasimpletime‐basedcriterionwould
provideasingle,objectivedefinitionofrediscov‐
ery–whateverthecauseofthegapinzoological
records.Conservationbodiescouldpotentiallyuse
thisdefinitiontoperiodicallyproducelistsofspe‐
ciesthatmaystillbeextantand,byextension,are
inneedofrediscovery.Thesecouldbecategorized
accordingtothetimesinceaspecieswaslastre‐
corded(e.g.<25yearsago,25–49yearsago,50–
100yearsago,>100yearsago,etc.).Oneadvan‐
tageofsuchasystemwouldbetomaintainand
extendthepracticeofbiogeographicalexpedi‐
tionstoremoteareas.Itwouldalsohelpguard
againsttheoveruseormisrepresentationofredis‐
109frontiersofbiogeography3.3,2011—©2011theauthors;journalcompilation©2011TheInternationalBiogeographySociety

coveriesinthemedia(Ladleetal.2009).Itwould
offeraviablealternativetotheuseoftermssuch
as‘possiblyextinct’(Butchartetal.2006)and
‘datadeficient’,andwouldensurebetterquality
ofdataforfuturebiogeographicalstudies.

Conclusions
Therediscoveryofaspeciesthatwasthoughtto
beextinctcangenerateglobalinterestandrepre‐
sentsarealopportunityforconservationiststo
reassertcorevaluesandraisefundsthatmayhelp
protectpoorlyknownhabitats.Moreover,redis‐
coveriesprovideauniquesourceofinformation
abouttherarestandleast‐knownspecies(forcer‐
taintaxa)thatcanbeusedtoinvestigatebio‐
geographictheoriesaboutrangelossandextinc‐
tion.Bothoftheseimportantagendaswould
benefitfromagreatersystematizationofthecon‐
ceptofrediscovery,acknowledgingthevarying
causes(bothsocialandecological)ofgapsinthe
temporalrecordsofrarespecies.
Insummary,thestudyofrediscoveriespro‐
videsawonderfulopportunitytoassessboththe
subtleecologicalandbiogeogeographicalcharac‐
teristicsofexceptionallyrarespeciesofwellstud‐
iedtaxasuchasamphibians,birdsandmammals,
andthefascinatinghistoricalandculturaltrendsin
zoologicalsurveyingandexploration.Considerable
effortsarebeingmadetountangletheseinteract‐
ingfactors(Fisher2011a,b;FisherandBlomberg
2011,Scheffersetal.2011),whiletherecenttar‐
getingof‘lostspecies’byinternationalconserva‐
tionNGOsisgeneratingconsiderableamountsof
valuablenewdata.Nevertheless,thelackofredis‐
coveredspeciesthatwerepreviouslywellknown
andwhichhadundergoneawelldocumented
processofpopulationdecline,fragmentationand
localextinction(Scheffersetal.2011)remainsa
worryingtrendforglobalconservation.

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EditedbyJanBeck
111frontiersofbiogeography3.3,2011—©2011theauthors;journalcompilation©2011TheInternationalBiogeographySociety