Aspects of habitat selection by adult dragonflies at a newly created pond in Vienna, Austria

4 Pages·1996·1.3 MB·English

by  Raab, R

Odonatologica25(4): 387-390 December I.1996
Aspects of habitatselection
by adultdragonfliesatanewly createdpond
inVienna, Austria
R. Raab¹,A.Chovanec² andA.K.Wiene²r
1 AntonBruckner-Gasse 2/2; A-2232Deutsch-Wagram,Austria
2 Umweltbundesamt, SpittelauerLande 5, A-1090Wien,Austria
Received December6, 1995/RevisedandAcceptedMay 10,1996
Investigationsoftheperchingsite selection byadultdragonflieswerecarriedoutat
the “Tritonwasser”,onthe “Donauinsel”. Special attention is drawn totheperching
behaviour of Orthetrum cancellatum and Crocothemis erythraea.Both spp. select a
great varietyofstructures andpreferably perch in heightsbetween groundlevel and
70cm. Crocothemis showed a strongerpreference forperching sites overthe water
surface. Other spp. observed were Coenagrionpuella,Erythromma viridulum and
Ischnura elegans.
INTRODUCTION
Theconservation ofprimary aquatic ecosystems as well as therestoration or
constructionofhabitatsare themostimportant elementsofsound dragonfly pro-
tection (e.g. MARTENS, 1991;MOORE, 1991).Conservation depends to alarge
extentuponunderstanding thefactorswhichdeterminethecomposition ofthedrag-
onfly fauna.Thereforeappropriate research is thekey forsuccess ofmanagement
practices; inthis connectionaspects ofhabitatselection(e.g.BUCHWALD, 1992;
CHOVANEC, 1993;WILDERMUTH, 1994)andcolonizationareof majorinter-
est(seealsoWILDERMUTH, 1991).
This paperdeals withthe selectionofperching sites by the following odonate
species occurring ata newly createdpondinVienna (Austria),the“Tritonwasser”:
Coenagrion puella, Erythromma viridulum, Ischnura elegans, Orthetrum cancel-
lationandCrocothemiserythraea. Withinthe investigation period23 species were
recorded,those5 were themostabundant.
* Paperpresentedatthe 13thInternational SymposiumofOdonatology,Essen,Germany,August20-
-25, 1995.
388 R. Raab,A.Chovanec &A.K. Wiener
STUDYAREA
The Tritonwasser isanartificial wetland, about2 hainsize,situated onthe“Donauinsel” (“Danube
Island”)inVienna. The waterbody wasconstructedin 1989/90ascompensationfortheloss ofaquatic
ecosystemsintheViennaDanubearea. The Donauinsel,with alengthofabout21kra, represents the
major elementoffloodprotection in Vienna, itis a highlyfrequentedrecreational area,where also
ecologicallypreciouszonesoccur.The initial plantingsofterrestrialvegetationaswell asofemergent
andsubmerged macrophytes,made inthe summerof 1990, favoured the developmentofadensebelt
of vegetationwhichprevents visitors fromreachingthe waterand creates ahabitat rich instructural
diversity. The study areahas been described by CHOVANEC et al. (1993),GOLDSCHMID &
GROTZER (1993)andCHOVANEC(1994).
BiotopeparametersoftheTritonwasser: the waterbody andthelittoral areasaretotallyexposedto
thesun;ahighdegreeofshoreline diversification wasreached bythe construction ofbeaches and two
islands;themaximum depthis about2.50m. About80% oftheshoreline isdominatedbydense reed
stands (Schoenoplectus lacustris, Typha angustifolia,Phragmitesaustralis inequalshares) and toa
minordegreeby Carexspp., Juncusspp., Sparganiumerectum, Irispseudacorus,Butomus umbellatus
andAlismagramineum;Myriophyllumspicatumis thehighlyabundant submergedmacrophyte spe-
cies which occursoverthe wholeareaasfloatingmats.
Recordingsofdragonfliescoloniz-
ingthe Tritonwasser havebeen car-
ried out since 1990,as a long-term
monitoringprogram (CHOVANEC,
1994).As shown inFigure 1,theto-
tal numberofspeciesincreased from
1 in 1990 to 26 in 1995 and the
number of autochthonous species
(records ofadults;observations ofre-
production/breedingbehaviour and/or
records oflarvae, freshly emerged
imaginesorexuviae) from 1 to 17.
Fig. I. Developmentofdragonflypopulation atthe “Triton- Duringthese sixyears, about 80 vis-
wasser”duringthe firstsixyears subsequentthe construction itsweremade tothe area.
ofthe habitat.
METHODS
Observationswereperformedinthe secondhalfofJuly 1994and July 1995.Atotalof12visitswas
made, 6between 14lhand 28“’ July 1994, 6 between 17“’ July and 1“ ofAugust 1995. Eachvisit was
made duringsunny weather,air temperatureswerebetween 20and 35°C.The 8morningvisitsusually
lasted fromabout9.00to 12.00h, the 4visits in theafternoon lasted from 12.00to 15.00hCentral
Europeantime.Duringeach visit,the variouslittoralzonesoftheTritonwasser werevisited,at every
homogeneousvegetationpatchthe dragonflyperching sites wererecorded. Therefore,the numbers
givenbelow refertothe observations rather thantotheexact number ofindividuals.
RESULTSAND DISCUSSION
PERCHING SITESOFCOENAGRION PUELLA,ERYTHROMMA VIRIDULUM
ANDISCHNURAELEGANS
In 1994 and 1995,Erythromma viridulum, Ischnura elegans and Coenagrion
Adult habitat selectionin aman-made pond 389
puella were the most abundantzygopteran species atthe Tritonwasser. Highest
numberofE. viridulumindividuals(males andfemales) recorded during one visit
- 1994:about425, 1995;about 1,770;I. elegans - 1994: 135, 1995: 108;C. puella
- 1994:34, 1995:26. Apparent preferences for Myriophyllum mats as perching
sites were shown by E.
viridulum. Dense reedstands
consisting of Schoenoplectus
lacustris, Phragmitesaustralis
and Typha angustifolia were
frequented by I. elegans. C.
puella preferably perched on
P. australisstems and on di-
verse structures, such as ele-
mentsoftheterrestrialvegeta-
tion near the shoreline or
Juncus sp. stems(Fig. 2).
PERCHING SITESOFMALE
ORTHETRUMCANCELLATUM
ANDCROCOTHEMIS
ERYTHRAEA
Thehighestnumberpervisit
of male Orthetrum cancella-
tum was estimated at 24 for
1994,andat 15for1995;Cro-
cothemiserythraea: 21(1994)
and42(1995).O. cancellatum
preferably perched on gravel
Figs 2-5. Perching sites ofvarious
species [n=numberofobservations]:
(2)aggregated(994and 1995datafor
both sexesofErythrommaviridulum
(n=7291), Ischnura elegans (n=946)
and Coenagrionpuella(n=237);- (3)
male Orthetrum cancellatum and
Crocothemiserythraea;- (4)heights
ofperchingsitesofmaleC.erythraea
(1994 n=86, 1995 n=185) and O.
cancellatum(1994n=84,1995n=65);
- (5) perching sites of male O.
cancellatum and C.erythraea above
land, above the shoreline and over
water.
390 R. Raab,A.Chovanec & A.K.Wiener
banks (especially in 1995)and on Phragmites stems;in both years C. erythraea
individualswere mostly perched on Phragmites stems (Fig. 3). In the two after-
noonsof1994,gravelbanks wereavoidedasrestingplace by bothspecies because
ofhighair temperatures(about 35°C) heating up thestones, aphenomenon also
describedbyASKEW(1988). Thehighproportion ofselected“diversestructures”
indicates thegreatvariety ofperching sitesofthese two species. “Diverse struc-
tures”compriseforexample terrestrialvegetation, Juncus,Butomus orCarexstands,
,
or a piece of wire sticking inthe sediment.A high proportion ofO. cancellatum
perching sites wereatground levelbecauseofthestrongselectionofgravel banks
and between 10and 70 cm; males of C. erythraea preferably rested in similar
places (Fig. 4).
Acleareraspect ofthespatialsegregationofbothspecies is depicted inFigure 5.
In both years, Crocothemis showed a strongerpreference forperching sites over
thewater surface.InthecaseofOrthetrum, theratiowas morebalanced,not least
because of thehigh numberof perching sites onthegravel banks. In 1995nearly
50% oftheperchings wereabove land.
ACKNOWLEDGEMENTS
The authors would liketothankULLIGOLDSCHMID (DepartmentofHydraulicEngineeringof
the MunicipalCouncil ofthe City ofVienna) fortheclose cooperationand ULLI STARKfor her
linguistic corrections.
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