Diurnalbehaviourandhabitatuseofnonbreeding
MarbledTeal, Marmaronettaangustirostris
Andy J.Green and MustaphaElHamzaoui
Abstract:ThediurnalbehaviourandhabitatuseofthegloballythreatenedMarbledTeal,Marmaronettaangustirostris, werestudiedinMoroccoandSpainfromOctobertoMarch.ThisisthefirststudyofnonbreedingMarbledTeal,the mostprimitivememberofthepochards(tribeAythyini).LikeotherAythyini,MarbledTealpairrelativelylate:only
35%ofindividualswerepairedbymid-March.Feedingwasmainlynocturnal,andlessthan2%ofdaytimewasspent feedingfromNovembertoMarch.Feedingbehaviourwassimilartothatofdabblingducks(tribeAnatini).Asteady increaseinswimmingactivityfromOctobertoMarchwasrelatedtoincreasedcourtshipactivityandraptor-avoidance behaviour.Tealselectedareasclosetotheshorelineandavoidedopenwater.Selectionofshorelinehabitatsanddis- tancetoshorelinecovariedwithmonthandbehaviourtype.TheMarbledTealisanaberrantpochardwithastronger ecologicalaffinitywiththeAnatini.
Résumé:Nousavonsétudiélecomportementdiurneetl’utilisationdel’habitatchezlaMarmaronettemarbrée,Mar- maronettaangustirotris,auMarocetenEspagne,d’octobreàmars;ils’agitd’uneespècemenacéedanstoutesarépar- tition.Cetravailconstituelapremièreétude,horsdelapériodedereproduction,delaMarmaronettemarbrée,espèce
laleplusprimitivedesAythyini.CommechezlesautresAythyini,l’accouplementestrelativementtardifchezlaMar- maronettemarbréeetseulement35%desindividusavaientunpartenaireaumilieudemars.L’alimentations’est
avéréesurtoutnocturneet,denovembreàmars,moinsde2 %delapériodediurneétaitconsacréeàl’alimentation.Le comportementalimentairedesmarmaronettesétaitsemblableàceluidescanardsbarboteurs(Anatini).L’augmentation progressivedel’activitédenageobservéed’octobreàmarsétaitreliéeàl’augmentationdelafréquencedescomporte- mentsdecouretàlafuitedesrapaces.Lesoiseauxsetenaientsurtoutprèsdelacôteetévitaientleszonesd’eau
libre.Lapréférencepourleshabitatscôtiersetladistancejusqu’àl’eauétaientencovariationaveclemoisetlecom- portement.LaMarmaronettemarbréeestunoiseauaberrantdanssacatégorieetadesaffinitésécologiquesplusmar- quéesaveclesAnatini.
[TraduitparlaRédaction]
Introduction
In North America, the dabbling ducks (tribe Anatini) and diving ducks or pochards (tribe Aythyini) are considered to fall into two distinct guilds throughout the annual cycle (e.g., Nudds 1983, 1992; Nudds and Wickett 1994). The structure of Anatidae communities in the Mediterranean region has been less studied, but is complicated by the pres- ence of Aythyini that show ecological affinities with the Anatini (Amat 1984; Livezey 1996; Green 1998a), particu- larly the Marbled Teal, Marmaronetta angustirostris, consid- ered the most primitive living member of the Aythyini (Livezey 1996). Recently, the first detailed studies of the breeding ecology of this globally threatened species have been made (Green 1998a; Green et al. 1999a). Here we
ReceivedJanuary19,2000.AcceptedAugust10,2000.
A.J.Green.1 EstaciónBiológicadeDoñana,Departmentof AppliedBiology,ConsejoSuperiordeInvestigaciones Científicas,AvenidaMaríaLuisas/n,41013Sevilla,Spain. M.ElHamzaoui.2 CentreNationaldelaRecherche Forestière,ChariaOmarIbnAlKhattab,B.P.763,
10050Rabat-Agdal,Morocco.
1Authortowhomallcorrespondenceshouldbeaddressed
(e-mail:).
2Presentaddress:6850DeerRunDrive,Alexandria, VA22306,U.S.A.
present the first study of its nonbreeding ecology, providing basicinformationvitalfortheconservationofthespecies.
Ourobjectiveswere(i)tocalculatetime–activitybudgets of Marbled Teal to assess how their diurnal behaviour and rhythms change between October and March, (ii) to assess their selection of the different wetland microhabitats avail- able, and how this habitat use covaries with behaviour, (iii) to identify their pairing chronology. Northern hemi- sphere Anatini and Aythyini typically form pair bonds anew each year (Oring and Sayler 1992). The Marbled Teal is highly unusual among northern hemisphere ducks in its sex- ual monochromatism and various features of its reproductive biology (Green 1998c), but no information was available about its pairing chronology. We compare our results with thosefromstudiesofotherAythyiniandAnatinitoshed light on the ecological similarities of Marbled Teal and on impliedtrendsintheevolutionofAnatidae(Livezey1986,
1991,1996).
Studyareas
DatawerecollectedatSidiBouGhaba(SBG,34°10′N,
6°39′W),abrackishclosed-basinlagoonwithalengthof
6kmandanareaof100haamongdunesontheAtlantic coast of northwest Morocco (Fig. 1) protected as a Ramsar SitewithinaBiologicalReservecovering702ha(Thévenot
1976; Morgan 1982; Hughes and Hughes 1992). SBG is
GreenandElHamzaoui2113
Fig.1.LocationofSidiBouGhaba(SBG)inMorocco(2)andLuciodelaFAOinSpain(1),anddetailsofSBG,showingthethree lagoonsectionsdescribedinthetext(A,B,andC)andthemouthoftheOued(River)Sebou.
2114Can.J.Zool.Vol.78,2000
Table1.Diurnaltime–activitybudgetsofMarbledTeal,Marmaronettaangustirostris,indifferent monthsatSidiBouGhaba(SBG)andLuciodelaFAO(FAO).
October,SBG
November,FAO
February,SBG
March,SBG
Note:Values,whicharegivenasthemean±SE,arepercentagesoftimespentineachbehaviour;nisthe numberofdiurnalhourlyperiods.
aIncludeswalking,drinking,andalertbehaviour.
extremelyimportantforMarbledTeal(hereinafterteal)in the nonbreeding season, but fewer than 10 pairs breed there and no nesting activity occurs before April (Green 1993,
1998c).
Water levels undergo major seasonal and annual variations andthelagoonisdividedintothreeparts(Fig.1):(A)a small permanent section (used by teal during the breeding seasononly)isolatedbyacauseway;(B)adeeper(maxi- mum 2.5 m), permanent brackish section subject to consid- erable human disturbance (local residents picnic at the site); (C) a shallow, temporary brackish to saline section (maxi- mum depth 0.7 m) strictly protected as a reserve. Emergent vegetation is restricted to a dense fringe along the shoreline, and waterbirds are readily observed through gaps in this fringe vegetation and from surrounding elevated vantage points (Fig. 1). Spot conductivity measurements were 14 mS (19February1995)and13mS(19October1997)insection B and 46 mS (13March 1995) and 29 mS (19 October 1997) insectionC.
A.J.G. also collected comparative data inLucio de la FAO (hereinafter FAO), an artificial lake 60 ha in area (fed by wa- ter extracted from an underlying aquifer) inside the northern edgeofDoñanaNationalPark(37°05′N,6°23′W)insouth- westSpain(Fig.1).Spotconductivitymeasurementswere
0.6–3.2mS(15November1995).Datawerecollecteddur- ing drought, when these teal occur particularly rarely in Spain (Green and Navarro 1997). Ringing recoveries suggest that birds at FAO and SBG are members of the same migra- torypopulation(NavarroandRobledano1995).
Methods
Behaviourandhabitatuse
Data were collected throughout the daylight period by means of instantaneous flock-scan sampling with a telescope (Altmann
1974).AtSBG,flockscanswereconductedat30-minintervalsby up to two observers who changed position during scans to cover all areas in use by teal. A few individuals were sometimes overlooked (e.g., sightings were obstructed by vegetation). Data were collected on 8 days between 12 and 21 February 1995, on 5 days between 12 and 21 March 1995, and on 17 and 18 October 1997; scans were scheduledscanstoensureequalcoverageforeachhouroftheday.
For each teal we recorded behaviour (see below); distance to the shoreline(inneredgeofthefringeofemergentvegetation(Fig.1), or the bank where there was no fringe) estimated visually in metres; type of shoreline habitat; species to which the nearest waterbird (hereinafter the nearest neighbour) belonged. Two thou- sand, four hundred, and fifty-three duck events were sampled in October,1851inFebruary,and1401inMarch.
The following behavioural categories were included: feeding (for subcategories see Green 1998a); sleeping(resting behaviour with head on back and eyes open or closed; moving birds were in- cluded in this posture); loafing (resting without head on back); comfort (preening, bathing, wing flapping, wing shivering, leg shaking, stretching, yawning, head shaking, bill dipping);swim- ming; flying; courtship (see Cramp and Simmons 1977 for dis- plays); aggression (intra- and inter-specific interactions); other (alert, walking, drinking). Shoreline habitat types were Phragmites communis;Typhaangustifolia;Scirpusspp./Juncusspp.(including J. acutus, J. maritimus, S. holoschoenus, S. maritimus); Carex sp.; Salicornia europea; open shores (sand, mud, or rocks). The avail- able length of shoreline types and area of open water less than and more than 10 m from the shoreline was calculated from a habitat map.
AtFAO,flockscanswereconductedat20-minintervalson15,
20,and21November1995.Owingtotherelativelysmallnumber oftealpresent,weonlyconsiderdataonindividualbehaviour(n=
417duckevents).
Pairingdata
The proportion of teal paired at SBG was estimated in February andMarch.Thepairstatusoftealisrelativelydifficulttoassess (cf.HeppandHair1983;Amat1990)becausethesexesarediffi- cult to distinguish and pairs show low levels of aggression to conspecifics. Pair status therefore could not be assessed during flock scans. Between scans, individuals seen moving were selected forcontinuousfocalsamplingandmonitoredforupto5mintosee if they were spatially associated with a particular conspecific. All equivocal cases were deleted from the sample. In March, compara- tive data were collected for Mallards,Anas platyrhynchos, and Green-wingedTeal,Anascrecca.
Statisticalanalyses
To construct diurnal time–activity budgets, behaviour was first expressedasthemeanpercentageofbirdsengagedinbehaviourof a particular category each hour (to weight scans by the number of individuals observed). Separate budgets were constructed for each month.Flock-scandatahaveproblemsofnon-independence.The
GreenandElHamzaoui2115
Fig.2.DiurnalrhythmsofMarbledTeal(Marmaronetta angustirostris)atSidiBouGhabainOctober(a),February(b), andMarch(c)(“06”represents06:00–06:59,etc.).“Locomotion” includesswimmingandflyingand“resting”includessleeping
andloafing.
behaviour and position of different teal at any moment partly de- pends on that of conspecifics in the same flock. The positions of birds at 30-min intervals are also interrelated. Thus, we used con- servative methods to analyse patterns of behaviour and habitat use. When analysing activity, we summed all data from each flock scan (individuals switched activities repeatedly within 30 min) and con- centrated on dominant behaviours recorded in every scan. When analysing habitat selection, we summed all data for each day (since individualsoftenremainedinthesamepositionforseveralhours). Inanalysesofvarianceinvolvingdistancetoshoreline,D,data
wereln(D+1)-transformedandweusedNewman–Keulsposthoc tests.
Results
At SBG, 100.4 ±5.5 teal (mean ±SE) were recorded per flockscan(n=25scans)inOctober1997,68.6±32.9(n=
27)inFebruary1995,and48.3±2.0(n=29)inMarch
1995.Peakcountswere266inOctober,105inFebruary, and 62 in March. At FAO in November 1995, 9.3 ±0.7 teal wererecordedperscan(n=45,peakcount=19).
Pairing
AsmallnumberoftealwerepairedbyOctober,although noprecisedatawerecollected.From15to23February,5% (n=20,95%confidenceintervalsonproportion(CI)=0–
25%)oftealwerepaired.From17to21March,35%ofteal
(n=249,CI=29–41%),76%ofMallards(n=132,CI=
68–83%),and64%ofGreen-wingedTeal(n=84,CI=53–
74%)werepaired.
As pairing progressed from October to March, teal showed a decreasing spatial association with conspecifics. In October, 92% of nearest neighbours recorded (n = 2543) wereconspecificswhentealconstituted7%ofthewater- birdsatSBG.InFebruary,68%ofnearestneighbours(n=
1691)wereconspecificswhen3%ofwaterbirdswereteal. In March, 32% of nearest neighbours (n = 1372) were con- specificswhen4%ofwaterbirdswereteal.
Time–activitybudgets
Diurnal time–activity budgets varied between months (Table1,Fig.2).AfterOctober,verylittlefeedingwasob- served (Table 1). Feeding was confined to crepuscular peri- ods (Fig. 2). Of 284 feeding events in October, 68% were upending, 30% were neck dipping, and 2% were bill dip- ping. In February and particularly March, locomotion (par- ticularly swimming) increased at the expense of resting, and courtshipactivityincreased(Table1,Fig.2).
Habitatselection
Distancetotheshoreline
Teal strongly selected wetland margins and avoided cen- tral,open-waterareas.Theareaavailablelessthan10mto theshorelinerepresentedonly26%ofthetotalareaatSBG in 1995 and 31% in 1997, yet it was used by 77% of teal scannedinFebruary,89%inMarch,and82%inOctober. On all 15 study days, the proportion of birds observed using this boundary area was higher than that expected at random (signtest,P0.0001).
Analysisofvarianceshowedthatthedistanceofeachteal to the water’s edge depended on its behaviour (sleeping, loafing,swimming,orcomfort,F[3,240] =14.6,P0.0001), month (F[2,240]= 37.4, P 0.0001), and the interaction be- tween the two (F[6,240]= 5.3, P 0.0001). Post hoc tests showed that in March and October, swimming teal were far- ther from shore than those engaged in other behaviours. In March, loafing teal were farther from shore than those that weresleeping.
2116Can.J.Zool.Vol.78,2000
Fig.3.DiurnalassociationwithdifferentshorelinetypesatSidiBouGhabaindifferentmonths(observeduse)relativetoavailability (expecteduse).Thedatawereweightedfordifferenttimesofthedaybycalculatingthepercentassociationwitheachhabitattypedur- ingeach1-hperiod,thentakingthemeanandSE(shownbyerrorbars).
Selectionofshorelinetype
Associations with shoreline habitats showed major sea- sonal differences (Fig. 3). In February and March, teal showed an association with T. angustifolia on all 13 study days (sign test, P 0.0001). In October, teal strongly se- lected open shores and made more use of P. communis habi- tats (Fig. 3). Selection of shoreline type by birds coming out of the water was more pronounced. In February–March,
87%ofbirdscomingoutofthewater(n=454)werein T.angustifoliaandonly9%wereonopenshores.InOcto- ber, all birds (n = 1005) were on open shores. These differ- ences were associated with a switch (from B to C; see Fig. 1) in the SBG section, where teal were concentrated, between1995and1997.
In March (but not in other months), association with edge habitatscovariedwithbehaviourtype(χ2 testonthenumber of scans in which each behaviour–habitat combination was recorded,χ2 =29.72,P0.001).Sleepingtealwerethose most strongly associated with T. angustifolia. Feeding teal wereassociatedwithfloodedS.europa(Fisher’sexacttest, P 0.02). No S. europa habitat was available in October, when 44% of feeding birds were associated with open shores and34%withT.angustifolia.
Discussion
As is typical in ducks of the subfamily Anatinae, Marbled Tealbreedintheirfirstyear(CrampandSimmons1977). Our study shows that although some teal are paired in Octo- ber, most individuals pair in March or later, shortly before breeding.Thisislaterthanmostdabblingducksbutsimilar to other Aythyini (Cramp and Simmons 1977; Hepp and Hair1983;BaldassarreandBolen1994).InSpain,courtship
andpairingarecompletedbysometealaslateasMayafter theyarriveatbreedingsites(NavarroandRobledano1995).
During the nonbreeding period, teal are mainly nocturnal foragers. In midwinter, almost no foraging was recorded during the day, while feeding continued after dawn and be- fore dusk in early and late winter, when nights were shorter; this is a common pattern in migratory ducks in winter (Paulus 1988; Michot et al. 1994; Green et al. 1999b). We found no evidence to support speculation (Livezey 1996) that teal are more crepuscular and less nocturnal than Aythya species. Thus, the idea that there has been an evolutionary shift from crepuscular to nocturnal activity in the Aythyini (Livezey1996)isnotsupported.
Throughout the annual cycle, the feeding behaviour of Marbled Teal is typical of Anatini (Green 1998a), and this is theonlyextantmemberoftheAythyiniwithnopropensity to dive. At SBG, both diurnal and nocturnal feeding were concentrated in section C (Fig. 1), and teal showed a prefer- ence for feeding in S. europa when it was available; faecal analysis showed that they fed on adult chironomids and S.europaseedsinFebruary(Green2000).
The tendency for teal to spend more time in locomotory activities as the nonbreeding period progressed from October to March may be linked to increased courtship activity, i.e., moretimespentswimminginsearchofpotentialpartners and courtship opportunities. However, the most important reason for locomotion appeared to be the need for escape be- haviour in response to overhead flights of female Marsh Harriers, Circus aeruginosus, and Hen Harriers, Circus cyaneus. In response to these overhead passes the teal invari- ably flew a short distance out on to open water, then swam slowly back to the shoreline habitats. The relative frequency of harrier flights increased between October and March.
GreenandElHamzaoui2117
Harriers have a similar effect on the behaviour of other win- tering ducks (Tamisier 1974; Euliss and Harris 1987), and suchpredatoractivitymayhelpexplainnocturnalforaging inteal(McNeiletal.1992;TamisierandDehorter1999).
Marbled Teal are associated with microhabitats along the shoreline and with emergent vegetation at SBG, FAO, and other nonbreeding and breeding sites (Green 1998b). At SBG, teal were closer to the shore, on average, than were otherwinteringducksexceptGadwall,Anasstrepera(Green
2000). However, microhabitat use at SBG also covaried with behaviour, swimming birds making the most use of open water (partly in response to harrier flights). Studies of inter- specificdifferencesinhabitatusehaveoftenfailedtotake into account the influence of behaviour (e.g., White and James 1978; Nudds et al. 1994, but see Heimsath et al.
1993), making results difficult to interpret (because differ- ences in diel rhythms may lead to changes in apparent habi- tat use when there are no real differences in selection of, for example,foragingorroostinghabitat).
The selection of T. angustifolia shoreline habitats in the central, permanent part of SBG in February and March 1995 contrasted with the selection of open shores in the southern, temporary area in October 1997. This switch may have been relatedtochangesinwaterlevelorflocksize,asthewater was higher and more teal were present in October. Deeper water and a larger flock size may reduce the predation risk (Pöysä1987;Gauthier-Clercetal.1998).
InspiteoftheclassificationoftheMarbledTealwithin theAythyini,thisstudyillustrateshowitsforagingecology ismoretypicaloftheAnatini.Intermsofwinterecology, the Marbled Teal only resembles Aythya species in its late pairing. For some reason (e.g., because low levels of intra- specific aggression permit access to food for unpaired birds), early pairing of teal may not bring the benefit of improved late-winter body condition observed in many Anatini (Tamisieretal.1995).
The results of our study illustrate the importance of con- serving a diversity of shallow, margin habitats in wetlands important to nonbreeding Marbled Teal. Such habitats re- quire protection from human disturbance (which prevents the teal from using the eastern margin of section B at SBG) and overgrazing or reed-cutting (which are widespread prob- lems at Moroccan and Spanish wetlands; Green 1993; Dakki andElHamzaoui1997).Particularattentionisalsorequired to locate and manage appropriately those areas that are im- portant for nocturnal foraging, which may be little used dur- ingtheday(McNeiletal.1992).
Acknowledgements
Thefieldwork wasfinanced by the Consejería de Medio Ambiente, Junta de Andalucía, and the Centre National de la Recherche Forestière. We are grateful to D. Gonzalez, A. El Hamzaoui,andS.Robertsforassistanceindatacollection and to M. Maghnouj for help in planning and arranging per- mits. J.A. Amat, T.C. Michot, W.A. Montevecchi, A. Tamisier, and an anonymous reviewer commented on earlier drafts. Thanks are also extended to M.L. Chacón, J.J. Chans, M. Ferrer, H. Garrido, F. Hiraldo, D. and K. Hoffmann, R. Pintos, Comite des Programmes de la Conservation de la
Nature(Rabat,Morocco),andTheWildfowlandWetlands
Trust(Slimbridge,U.K.).
References
Altmann, J. 1974. Observational study of behaviour: sampling methods. Behaviour,49:227–267.
Amat, J.A. 1984. Ecological segregation between Red-crested Pochard Netta rufina and Pochard Aythya ferina in a fluctuating environment.Ardea,72:229–233.
Amat, J.A. 1990. Age-related pair bonding by male Eurasian Wigeons inrelationtocourtshipactivity.Auk,107:197–198.
Baldassarre, G.A., and Bolen, E.G. 1994. Waterfowl ecology and management.JohnWileyandSons,NewYork.
Cramp, S., and Simmons, K.E.L. 1977. Handbook of the birds of Europe,MiddleEastandNorthAfrica.Vol.1.OxfordUniver- sityPress,Oxford.
Dakki, M., and El Hamzaoui, M. 1997. Rapport national sur les zones humides (Maroc). MedWet report, Administration des Eaux et ForêtsetdelaConservatióndesSols,Rabat,Morocco.
Euliss, N.H., and Harris, S.W. 1987. Feeding ecology of Northern Pintails and Green-winged Teal wintering in California. J. Wildl. Manag.51:724–732.
Gauthier-Clerc, M., Tamisier, A., and Cezilly, F. 1998. Sleep– vigilance trade-off in Green-winged Teals (Anas crecca crecca). Can.J.Zool.76:2214–2218.
Green, A.J. 1993. The status and conservation of the Marbled Teal Marmaronetta angustirostris. IWRB Spec. Publ. No. 23, Interna- tionalWaterfowlandWetlandsResearchBureau,Slimbridge,U.K.
Green, A.J. 1998a. Comparative feeding behaviour and niche orga- nizationinaMediterraneanduckcommunity.Can.J.Zool.76:
500–507.
Green, A.J. 1998b. Habitat selection by the Marbled Teal Marma- ronetta angustirostris, Ferruginous Duck Aythya nyroca and otherducksintheGöksuDelta,Turkeyinlatesummer.Rev. Ecol.TerreVie,53:225–243.
Green, A.J. 1998c. Clutch size, brood size and brood emergence in the Marbled Teal Marmaronetta angustirostrisin the Marismas delGuadalquivir,southwestSpain.Ibis,140:670–675.
Green, A.J. 2000. The habitat requirements of the Marbled Teal (Marmaronetta angustirostris Ménétr.): a review. In Limnology and aquatic birds: monitoring, modelling and management Proceedings of the 2nd Societas Internationalis Limnologiae In- ternational Congress, Yucatán, Mérida, Mexico. Edited by F.A. Comín,J.A.Herrera,andJ.Ramírez.pp.131–140.
Green, A.J., and Navarro, J.D. 1997. National censuses of the Mar- bledTeal,Marmaronettaangustirostris,inSpain.BirdStudy,
44:80–87.
Green,A.J.Navarro,J.D.,Dolz,J.C.,andAragoneses,J.1999a.
BroodemergencepatternsinaMediterraneanduckcommunity. BirdStudy,46:116–118.
Green, A.J., Fox, A.D., Hughes, B., and Hilton, G.M. 1999b. Time– activity budgets and site selection of White-headed Ducks (Oxyuraleucocephala)atBurdurLake,Turkeyinlatewinter. BirdStudy,46:62–73.
Heimsath, S.F., Lopez de Casenave, J., Cueto, V.R., and Cittadino, E.A.1993.UsodehabitatenFulicaarmillata,Fulicaleuco- pterayGallinulachloropusdurantelaprimavera.Hornero,13:
286–289.
Hepp,G.R.,andHair,J.D.1983.Reproductivebehaviorandpair- ingchronologyinwinteringdabblingducks.WilsonBull.95:
675–682.
Hughes, R.H., and Hughes, J.S. 1992. A directory of African wetlands. International Union for the Conservation of Nature
2118Can.J.Zool.Vol.78,2000
andNaturalResources,Gland,Switzerland,Cambridge,U.K., andNairobi,Kenya,UnitedNationsEnvironmentProgramme, Cambridge,U.K.,andWorldConservationMonitoringCentre. Livezey,B.C.1986.Aphylogeneticanalysisofrecentanseriform
generausingmorphologicalcharacters.Auk,103:737–754. Livezey,B.C.1991.Aphylogeneticanalysisandclassificationof
recentdabblingducks(tribeAnatini)basedoncomparativemor- phology.Auk,108:471–507.
Livezey,B.C.1996.Aphylogeneticanalysisofmodernpochards
(Anatidae:Aythyini).Auk,113:74–93.
McNeil, R., Drapeau, P., and Goss-Custard, J.D. 1992. The occur- rence and adaptive significance of nocturnal habits in waterfowl. Biol.Rev.Camb.Philos.Soc.67:381–419.
Michot, T.C., Moser, E.B., and Norling, W. 1994. Effects of weather and tides on feeding and flock positions of wintering Redheads in Chandeleur Sound, Louisiana. Hydrobiologia,
279/280:263–278.
Morgan, N.C. 1982. An ecological survey of standing waters in North West Africa: III. Site descriptions for Morocco. Biol. Conserv.24:161–182.
Navarro, J.D., and Robledano, F. (Coordinators). 1995. La Cerceta Pardilla Marmaronetta angustirostris en España. Instituto Nacional para la Conservación de la Naturaleza – Ministero de Agricultura, Pesca y Alimentación (ICONA-MAPA) Colección Técnica, Instituto NacionalparalaConservacióndelaNaturaleza,Madrid,Spain.
Nudds, T.D. 1983. Variation in richness, evenness and diversity in divinganddabblingduckguildsinprairiepotholehabitats.Can. J.Zool.61:1547–1550.
Nudds, T.D. 1992. Patterns in breeding waterfowl communities.In Ecology and management of breeding waterfowl. Edited by B.D.J. Batt, A.D. Afton, M.G. Anderson, C.D. Ankney, D.H. Johnson, J.A. Kadlec, and G.L. Krapu. University of Minnesota Press,MinneapolisandLondon.pp.540–567.
Nudds, T.D., and Wickett, R.G. 1994. Body size and seasonal co- existenceofNorthAmericandabblingducks.Can.J.Zool.72:
779–782.
Nudds, T.D., Sjöberg, K., and Lundberg, P. 1994. Ecomorpho- logicalrelationshipsbetweenPalearcticdabblingducksonBal- ticcoastalwetlandsandacomparisonwiththeNearctic.Oikos,