J. Field Ornithol., 62(3):399-402
USE
OF
TONGUE-FLICKING
SNOWY
TERRY
BEHAVIOR
EGRET
BY
THE
L. MASTER •
BiologyDepartment
Lehigh University
Bethlehem,Pennsylvania18075 USA
Abstract.--Snowy Egrets (Egrettathula) were observedusing the tongue-flickingfeeding
techniqueduringfull moon,springtide periodsin a southernNew Jerseysaltmarsh.Egrets
fed mainly on two speciesof. fish, which were normally confinedto salt marsh pannes.
Spring tides floodedthe marsh to a depth of 15-25 cm causinga dispersalof fish over the
entiremarshsurface.The resultingdrop in prey densitycouldhaveinitiatedthe useof this
prey-attractingforagingtechnique.Tongue-flickingmay havebeenmoreefficientthan other
feedingtechniqueswhen prey were widely dispersed.
UTILIZACI•N
DE LA T•CNICA
LENGUA
INDIVIDUOS
POR
DE MOVIMIENTO
DE EGRETTA
DE LA
THULA
Sinopsis.--Enun anegadosalobredel sur de New Jersey,seobservaron
(en nochesde luna
11ena)a individuosde garza blanca(Egrettathula) utilizar la t•cnica de movimientode la
lenguapara atraer prcsas,duranteel periodoprimaveralde incrementoen los nivelesde
agua.Las garzassealimentaronprincipalmentede dosespecies
de peces,que normalmente
estrinconfinados
a ancgados
salobres.
DeNdoalas aguasprimaverales,
el anegadoseinund6
hastauna profundidadde 15-25 cm, causandouna dispersi6nde lospecesa travis de toda
la superficiede •ste. E1 resultantedecrecimientoen la densidadde presaspuede haber
iniciadoel patr6ndeconducta
demovimiento
delengua,paraatraera lospeces.Estat•cnica
de forrajeopuedeque seamilseficienteque otrasutilizadaspot las garzascuandolospeces
utilizadoscomoalimento,estrindispersos.
Snowy Egrets (Egretta thula) use a greater variety of foraging techniques than any other North American heron (Kushlan 1976). One of
the leastinvestigatedand understoodof thesetechniquesis tongue-flicking
(Buckleyand Buckley 1968, Parks and Bressler1963), which Kushlan
(1973) found to attract fish. Observationsof tongue-flickingwere made
as part of a more comprehensive
investigationof the effectsof prey and
environmentalcharacteristics
on SnowyEgret foragingstrategies(Master
1989).
STUDY
AREA
The salt marsh where observations
were made is located near the town
of StoneHarbor, Cape May County, New Jersey.Under normal tidal
conditions,the marsh is not inundatedduring either of the two daily high
tides.Spring tides,which coincidewith the full moonand last from 6 to
8 d, inundatethe marsh surfacefor a periodof severalhoursto a depth
of 15-25 cm. Tidal height is dependentupon monthlyand daily tidal
fluctuations.The maximuminundationdepthof 20-25 cm usuallyoccurs
during the eveninghigh tide on the day of the full moon in July and
August.This period lastsfor approximately 1-2 h.
• Currentaddress:
BiologyDepartment,East Stroudsburg
University,East Stroudsburg,
Pennsylvania 18301 USA.
399
400]
7'.L. Master
J.Field
Ornithol.
Summer
1991
METHODS
All of the data reportedwere collectedduring 15 h of observationon
fiveJuly/Augustfull-moondaysovera periodof 3 yr. Theseparticular
dayswere chosenbecausemaximum water depth presumablyequated
with maximumprey dispersal.Tongue-flickingwas alsoobservedduring
springtidesof lessermagnitudethroughoutthe study.
Detailedforagingobservations
weremadeonlyon SnowyEgretslocated
within 150 m of the 10.5-m-high observationtower used during this
study. Egrets were chosenin the order in which they were discovered
and observationcontinueduntil they flew away, movedout of sightor
stoppedfeeding(Willard 1977). Only data from thoseindividualsobservedfor at least 10 min were includedin foraginganalyses.All individualsthat engagedin tongue-flickingdid so for the entire observation
period. Fish densitywas measuredusingthe Petersenmark-recapture
technique.
RESULTS
During the early stagesof flooding(1-10 cm in depth),SnowyEgrets
arrivedon the marshand beganfeeding.Commonforagingtechniques
usedat thistime includedstandandwait, walk slowly,walk quickly,run
and hop (Kushlan1976). At maximumdepth, 19 of the SnowyEgrets
observed
on all sampledays(62% of the total observed)
usedthe tongueflicking feedingtechnique.With the exceptionof five individualsseen
using the techniqueon large pannes(>1000 m2), tongue-flickingwas
observedexclusivelyduring springtidesthroughoutthe 404 h of observation accumulatedduring all aspectsof this project.
The useof this feedingtechniqueduringspringtidesmay havereflected
changesin the distributionof the SnowyEgret'smajor prey items,the
Mummichog(Fundulusheteroclitus)
and Sheepshead
Minnow (Cyprinodonvariegatus)
(Master 1989). During non-springtide periods,these
fisheswerefoundin tidal channelsandisolatedsaltmarshpanneswhere
egretsnormallydid mostof their foraging.The mean densityof fish in
panneswas65.6 + 1.5 (SD) fish/m2of pannesubstrate(n = 33) (Master
1989). During springtides,fishesdispersedfrom theseconfinedareas
with the risingwater levelwhich resultedin a changein density.Fish
densityoverthe marshsurfacedroppedto only 0.30 + 0.10 fish/m2 (n
= 54) during theseperiods(Master 1989).
DISCUSSION
The useof whatKushlan(1973)described
asa prey-attracting
behavior
suggests
that egretsmay havebeenminimizingthe energeticcostof foraging. Egret steppingrates have been used as an indication of effort
expended
duringforagingbouts(Hafneret al. 1980).SnowyEgretswere
nearlystationary
whenusingtongue-flicking,
whichreduced
their stepping rate significantly
belowthe rate for otherspringtide feedingtechniques(Table 1). Kent(1986)determined
that standing
egretsrequired
lessenergythanthoseusingactiveforagingtechniques.
Presumably,
less
Vol.62,No.3
Tongue-flicking
in Snowy
Egrets
[401
TABLE1. Comparisonof the mean (+SE) steppingrate, capturerate and captureefficiency
among spring tide foraging behaviors.
Foraging behavior
Steps/min
Captures/min
Captures/strike
Tongue-flicking(n = 10)
Other behaviors(n = 21)
0.38 + 0.03
0.44 + 0.04
0.38 + 0.02
12.70 + 0.33a
0.39 + 0.01
0.37 + 0.01
• P < 0.001; Wilcoxon two-sample test.
steppingreducedenergyexpenditureduring foragingbouts,althoughthe
energeticcostof tongue-flickingitselfremainsunknown.Conversely,capture rate (captures/min)and captureefficiency(captures/strike),when
using tongue-flicking,were comparablewith other spring-tide feeding
techniques(Table 1). Therefore, tongue-flickingSnowyEgretsacquired
similar quantities of prey when comparedto individuals using other
techniquesbut may have expendedlessenergyin the process.Kushlan
(1973) suggested
that egretsusefeedingbehaviorsthat maximize energy
intake and minimize energy expenditure under specificenvironmental
conditions.Energy efficientprey size selectionhas been noted in both
the SnowyEgret and closelyrelated Little Egret (E. garzetta)(Cezilly et
al. 1988, Itzkowitz and Makie 1986).
A major problemin foragingstudiesis that prey distributionpatterns
are usually not known preciselywhen predatorsare present(Kushlan
1978). Perceivedchangesin prey distributionare often inferred by observingthe foragingsuccess
of predatorsrather than by direct sampling
of the prey population (Hafner et al. 1980). Consequently,it is often
difficult to imply that changesin the foragingbehaviorof predatorsare
the result of changesin prey distribution.Erwin et al. (1985) did relate
prey distributionto Little Egret foragingbehaviorin different habitats.
They observedthat lessactiveforagingtechniqueswere usedin the habitat
with the mostcoverand lowestprey density.
Spring tides in southernNew Jersey provideda natural experiment
regardingthe relationshipbetweenprey distributionand foragingbehavior within a single habitat. Observationssuggestedthat use of the
relatively sedentarytongue-flickingbehaviormay have also been a responseto reducedprey density.
ACKNOWLEDGMENTS
I wishto thank Murray Itzkowitz, Daniel Klem, Jr., R. Michael Erwin and Paul Buckley
for helpful commentsregardingthis manuscript.I would alsolike to thank Lisa Ruth and
Michelle Frankel for assistingwith field observations.This researchwas supportedby a
Grant-in-Aid of Researchfrom SigmaXi aswell as grantsfrom the PennsylvaniaAcademy
of Scienceand the Lehigh University BiologyDepartment.
LITERATURE
CITED
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r.L. Master
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Summer
1991
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Received16 Sep. 1990; accepted14 Jan. 1991.