Corella,2004, 28(3): 61-67 SEASONALPATTERNS IN ABUNDANCEOF WATERFOWL(ANATIDAE) AT A WASTESTABILIZATION POND IN VICTORIA ANDREW J. HAMILTONIr and IAIN R. TAYLORI 'AppliedOrnithology Group, Johnstone Centre, School of Environmentaland InformationSciences, Charles Sturt University,PO Box 789, Albury, New SouthWales. Auslralia 2640 :Correspondingauthor (Currenl Address): Primary Industri€s Rcscarch Victoria (Knoxfield), Privatc Bag 15, FerntreeGully DeliveryCentre, Victoria, Australia3156 Received:2 Novenber2003 The seasonal abundanceof waterfowlon a waste stabilizationpond at the Western TreatmentPlant, Victoria, Australia,was studied over two years. The abundancesof species that are considered to be highly dispersive, such as the Pink'eared Duck Malacorhynchusmembranaceus and Grey Teal Anas gracilis, were erratic and inconsistentacross the two years. For other species, such as the AustralasianShoveler /nas rhynchotis,Blaak Swan Cygnus atratus, Pacific Black Duck /nas superciliosaand AustralianShelduck Tadoma tadornoides,mote consistentpatterns were observed each year. Most species used the site during what would be expectedto be their non-breedingseason. Australian Shelducks appeared to use the site as a late-spring/early-summermoulting reluoe. INTRODUCTION Pond Nine of the WTP, and draw comparisonswith previouslypublished work. The Westem Treatment Plant (WTP) at Werribee. Victoria, is known to support large numbers of waterfowl of several species (Lane and Peake 1990), and forms part MATERIALSAND METHODS of a Wetland of International Significance (Ramsar ConventionBureau 1984). A Iargewaste stabilization pond Study site within the WTP, known as Pond Nine in the Lake Borrie The WTP occupies an area of 10851 hectaresand is situated35 system,is consideredto be of particular importancefor kilometrcs wcst of Melbourne on the shores of Por( Phillip Bay waterfowl and other waterbirds(Elliget 1980; Hamilton (38"00'5, 144"34'E).A location map is provided in Hamilron ?r dl. (2004). Observations for rhe present study were made at a wasle 2002; Hamilton et al. 20021Hamilton er dl., press). in stabilization pond known as Pond Nine, part of a series of ponds that There is little published quantitative information on make up (he Lake Bonie system. Unlike the orher pond systenrsar lhe seasonalchanges in abundanceof waterfowl at the site. WTP, the Lake Borrie ponds are inegularly shapcd and of differing Sewagetreatment changes will be implementedat the WTP sizes. Much of the Lake Borrie sysrcm was originally a natural wetland thal was in 2005, which havethe potentialto affect the usefulness divided into a series of 30 waste stabilizalion ponds through the construction of impoundments in 1936. Pond Nine is the lafgest of of the site, includingthe Lake Borrie ponds, to waterfowl lhese, covering an area of 109 hectares. It is also lhe only pond in the (see Hamilton et al. 2002), so information on seasonal sysl€m wilh a stand of dead trees (mostly Melaleuca lanceolata). me patternsof abundancecould be useful in monitoring anv averagc waler depth is 60 centimerres (Cartwright 1996, unpubl. data). chrngesand lbr developingmanagement strategies foi this Further details of the functioning of the Lake Borrie waste slabilizalion ponds Ramsarprotected wetland. with respect to sewage treatment and ecology can be found in Hamillon (2002). Seasonalmovements of Australian waterfowl are believed SanqLint proto.ol to be influencedby rhe availability and depth of inland temporarywetlands (e.9. Morgan 1954;Frith 1957;Frith Dala used here were collecled as parl of a wider study on the diumal 1959;Braithwaite and Stewart1975; Crawford 1979;pert activity budgels of waterfowl at pond Nine, the sampling protocol for 1997). It has been suggested that inland temporary which is describedin derail in Hepworrh and Hamitron (2001) and Hamilton ?/ al. (2002). In sumrnary, tloodwaters provide an abundanceof food for waterfowl surveys were made from defined observationpoints on the €mbankmenl using a Leica@ (Braithwaite and Frith 1969), Tclevid 7? and hence offer suitable telescope(20-60 x zoom magnification).Sampling, which involved (he breeding conditions for many species. Conversely, countrng total numbcr of birds on the pond, was conducted at five perrnanentwetlands, such as waste stabilizationponds, may evenly spaced times of day: sunrise, mid,morning, midday, mid- be used as non-breeding refuges (Braithwaite and Stewait afternoonand sunset.It took approximatelyone hour to sample the entlre pood: hence sampling for each time of day was 1975). Most of the ideas on waterfowl movements begun 30 minulcs are belore the midpoinr of rhe sampting period (e.g. 30 basedon either banding minutes before studiesor more commonlv. on sunrise). Sampling was undertaken on 47 dalesi lfuee times a month comparisonsof seasonrlchunges in abunJancear particular ,rom ll July 1998to 20 June 1999and then at approximatelymonthly rocauons. rntervalsfrom I Augusr 1999ro 9 Augusl 2000. For rhe Hldhead A\!h)a au\ttaltt. The aim of this study was to quantify seasonalchanges d drring specres.ir $rj nece\sdry . to determine how long individuals stayed underwater during a dive in the abundanceof the main watefowl species so found at that no birds were misscdwhilst surveying.In a preliminarysludy, the A. Hamilton and L Taylot: Abundance of walerfowl at waste stabilization oonc, Corella 28(3) dive times of 70 birds were measured.The maximum dive durarion was numbersto occur from late summer to early autumn found to be 25 seconds (mean = 13.4 seconds).Thus, each ficld in of view each year (Fig. 2t. Numbers was observed for at lcasr 25 secondsso thal birds surfacing from a dive, of Crey Teal and Chestnur thal would nor have been seen in the initial scan. could be observed. Teal varied greatly from month to month, with no discerniblepattern (Figs 3 and 4). The PacificBlack Duck Data p'es?, ation was most abundantfrom late summer to mid-autumnof both years (Fig. Both daily average and maxirnum values were presentedfor (he 5). The nurnbersof Hardhead(Fig. 6) seasonal abundance of waterfowl. Daily maxima are particularly followed a very similar pattem to that for the pink-eared meaningful for species rhal show diumal trends in abundance since a Duck. The largest numbers, approximately 8 000 site could still have been importanl to a species at a parricular time of individuals,occurred at the first samplingdate on ll July year even if it was only used by it at certain rimes of day_ Thcre was 1998,with all subsequentcounts some drurnal variation ir abund:lnce of certain walerfowl species (see being lessthan half this Hamiltoo e/ al. 2002) so this approach was justifier:t.it was not number.The AustralianShelduck showedclear oeaksin appropriate to present a mean rvith an eslimare o{ error (e.g. standard abundancein Novembereach year (Fig.7). At this time crror or standard deviarion) for each dale sincc rhe five valuis for each many of the birds observedwere moulting and flightless. date were pseudoreplicatcsof a day. The Black Swan was most abundantfrom mid-summerto mid-autumn(Fig. 8). RESULTS Pink-eared Ducks were presentat the site mainly Small numbersof other waterfowl were seenoccasionally betweenApril 1999and March 2000, with peaknumbers in the sludy area.One or rwo individualsof FreckledDuci between Octoberand December, but therewas no evidence Stictonetta naevosa occurred on eight sample dates, and ol a repeated seasonalpattern over two years(Fig. l). For from one to five Blue-billedDucks Oxynraoustralis were AustralasianShovelers there was a tendencyfor highest seenon 20 sampledays. € oooo (n 5 5000 I qooo E j sooo 2000 1000 0r sFflBSS3E3338o>c.=>.=R:***i 6Zsis532sSS- Date Figurel."'ca.fo,IalabundanG0JPi*.eor?dDuckat.PondNine'Da*shadi8rprsen|sdoi|ytneanabwuJante;whi|efpresen|sdaiI!|nhun| abur]ance'InbeIson.l'axi:ide'lo|elk'fntdayoftheno|h'Thejr:tvniteiateisinlnrwit|t|he'y'ais'andi|elastisle September,2004 A. Hamillon and !. faylor Abundanceof waterfowlat waste stabilizataonpond 3500 3000 2500 o d) 2000 6 o o 1500 E : z 1000 500 0r 00 cD o) o) o)oo)o) 333333 ;Ftr z:=j 3095E9= Date Figrrc 2. Searonolabrunlance o.f Australaian Shovelerat PondNine. Dark shadingrepresents daiLy nean abundance:white reprcsents daily matinlum abu||dan.e'LabeLson,x'tLtisdenotew|irstdayoI|he,no|l|h.The1irstsanple.la|eisinline\|i|h|||e,J'd|is'and|IrlaS| 1600 1400 1200 -u '1000 m b 800 o E 600 zl 400 200 0 qFqsssqsEooo ,l doi!*9rd"!!jE=:>= Date Figtre 3 Seannal abundanrc of Grey Teal Pond.Nke. Dark shading 't .at reprcsent^ dailJ mean abunda ce: whire represe ts daih) ,naxirum abu danu. L'lhels ott L\is denote the dav of the nnnth. Tt 'y Jirst lirst sanole date ir in line with rhe tis, and the Iasri:; at the end oJ rtt! x .\i\. 64 A. Hamilton and l. Taylot: Abundance of waterfowl at waste stabilization oond Corella28(3) 1400 1200 1000 ! o E 800 a.) o 600 E f z 400 200 0 RPPA :B i.iYY 'a ;> Date Figwe4.Seasonalabun.lanQoJ.Ches|nutTeatatPortNine.Darhadirrepresentsdoil!n|eanabundance;whilerepresen1sdailyn|axin|un1abundance' 't' Inbels ott 'y'ajj,ir, ,x @is denote the Jirst day of the tnonth.nrc rtN sample date ii in line n'ith the and the laj i; at ttrc etd ol the aris. 100 90 80 70 ! m 60 o 50 -oQ) E 40 = z 30 20 10 0 qsqss SSFBBq 3o9E s I aoi5sg= Date Fi9ue 5 Seasonal abu,tdanrc of Padfc Black Du.k at Powi Nine. Dark shading fpresents daily Dredn abundance: white represents daiLy naximunt abundan.e lnbeb 'x' 'y' 't, on aris denote lE fnt .lay of tlrc nonth. The jtst su pte date is in line wittt the .Ltir, and the tast is a! the en(t of the stabilizationpond 65 September,2004 A. Hamiltonand t. Taytot:Abundance ol waterfowlat waste 600 500 € 400 d] : 300 o -o E l z 200 100 6qs$ S E E E Date Fi}urc 6. SeasoMI obundn .e of Hardhead at Poul Nik.. Dark shadnr represe ts d!1ily nean abundance; white rprsentr dail-'r marimum abundane 'r'aris 'y'ais, 'x'arirl Lbels on denote the Jirst dat of the nonth.