October 1991] ShortCommunications 969 Natural Environment ResearchCouncil grant GR3/ LINDEN, M., & A. P. MOLLERß 1989ß Cost of repro- 7249. duction and covariation of life history traits in birds. Trends Ecol. Evol. 4: 367-371. LITERATURE CITED NUR, N. 1984. The consequencesof brood size for breeding Blue Tits I. Adult survival, weight ASKENIVIO,C. 1979. Reproductiverate and the return change and the cost of reproduction. J. Anim. rate of male Pied Flycatchers.Am. Nat. 114:748- Ecol. 53: 479-496ß 753. 1988a. The consequencesof brood size for COHEN,J. 1988. Statistical power analysis for the breeding Blue Tits III. Measuring the cost of re- behavioral sciences,second ed. New Jersey,Law- production: survival, future fecundity and dif- rence Erlbaum Assoc. ferential dispersalßEvolution 42: 351-362ß DESTEvEN,D. 1980. Clutch size, breeding success ß 1988b. The costof reproduction in birds: an and parental survival in the Tree Sparrow (Iri- examination of the evidenceß Ardea 76: 155-168. doprocnebicolor). Evolution 34: 278-291. --. 1990. The costof reproduction in birds, eval- DIJKSTRA,C., A. BULT, S. BIJLSMA,S. D^AN, T. MEIJER, uating the evidence from manipulative and non- • g. ZIJLSTRA.1990. Brood size manipulations manipulative studies. In Population biology of in the Kestrel (Falco tinnunculus):effects on off- passerinebirds, an integratedapproach (J. Blon- spring and parent survival. J.Anim. Ecol.59: 269- del, A. Gosler,J. D. Lebreton,and R. McCleery, 285. Eds.).Berlin, Springer-VerlagPressß FLEISS,J. L. 1981. Statistical methods for rates and ORELL,M., & K. KOIVULA. 1988. Costof reproduction: proportions, second ed. New York, J. Wiley and parental survival and production of recruits in Sons. the Willow Tit Parusmontanus. Oecologica 77: 423- FORBES,L.S. 1990. A note on statisticalpower. Auk 432. 107: 438-439. PETTIFOR,R. A., C. M. PERRINS,& R. H. McCLEERY. GUSTAFSSON,L., & W. J. SUTHERLAND.1988. The costs 1988. Individual optimization of clutch size in of reproduction in the Collared Flycatcher Fice- Great Tits. Nature 336: 160-162. dula albicollis. Nature 335: 813-815. REID,W. V. 1987. The cost of reproduction in the HARRIS,M.P. 1970. Breedingecology of the Swal- Glaucous-wingedGull. Oecologica74: 458-467ß low-tailed Gull Creagrusfurcatus. Auk 104: 470- ROSK•Fr,E. 1985. The effect of enlarged brood size 480. on the future reproductive potential of the Rook. HEGNER,R. E., & J. C. WINGFIELDß1987. Effects of J. Anim. Ecol. 54: 255-260. brood-sizemanipulation on parental investment, SOK•L, R. R., & F. J. ROHLF. 1981. Biometry, second breeding success,and reproductive endocrinol- ed. San Francisco, W. H. Freeman and Co. ogy of House Sparrows.Auk 104:470-480. TOFT,C. A., & P. J. SHEA. 1983. Detecting commu- KORPIM;(m,E. 1988. Costsof reproductionand suc- nity-wide patterns: estimating power strength- cessof manipulated broods under varying food ens statistical inferenceß Am. Nat. 122: 618-625. conditionsin Tengmalm'sOwl. J.Anim. Ecol.57: 1027-1039. Received19 September1990, accepted26 May 1991. Courtshipof Ducklingsby Adult Male Chiloe Wigeon(Arias sibilatrix) GWEN BREWER1 JamesFord Bell Museum of NaturalHistory, University of Minnesota,10 Church Street SE, Minneapolis,Minnesota 55455 USA Unlike mostbirds with seasonalpair bonds,many lead them away from other birdsßWhen femalesshow waterfowlpair muchin advanceof the next breeding their preferencefor one male and rejectionof others season(Rohwer and Anderson1988). For example,in by giving Inciting displays,temporary associations Holarcticdabbling ducks (Anatini), courtship and pair between males and females are formed. As bonds formationoccur up to 8 monthsbefore breeding be- strengthen, the members of a pair maintain close gins (Hepp and Hair 1983).During the early period proximity, synchronize their activities, repel rivals, of bond formation,males court femalesand try to and perform displays that reinforce the bond (Mc- Kinney in press). Pair bonds continue to be tested during spring migration and after arrival on the •Present address:Department of Biology, Frost- breedinggrounds, although most birds are pairedby burgState University, Frostburg, Maryland 21532USA. this time. 970 ShortCommunications [Auk, Vol. 108 Several hypothesesexist to accountfor the early binations of these characteristics. I identified broods timing of pair formation in the Northern Hemisphere throughout study periodsby comparingthe size and (reviewedby Rohwerand Anderson1988). Generally, age of the ducklings,the locationof the brood, and the balancebetween benefits from pairing to both the plumagecharacteristics of parents(both male and sexesand coststo malesis of major importance.Al- female attend broods)with previous information and though participatingin courtshipmay be energeti- sketchesof both parents (Brewer 1990). Ducklings cally costly to females as well as males, females are were assignedto one of seven plumage classes(Ia-c, expectedto pair as soon as possiblebecause of the IIa-c, IIIa; Gollop and Marshall 1954)and assignedto benefits(such as enhancedfeeding efficiency)that age groups on the basis of data from 15 known-age they receive when paired. Males must balance the broods(those first sighted within 1-3 days of hatch- benefitsof pairing againstthe costsof mate defense ing). I could determine the sex of ducklings ca. 8 and vigilance, so that the exact timing of pair for- weeks of age (classIIc) from wing patterns (males mation will be determined largely by the male. have darker speculaand bright white upper wing Although the courtship displays of most tropical coverts)and from the presenceof a two-syllablewhis- and SouthernHemisphere dabbling ducks have been tle given only by males (method confirmed in cap- described(Johnsgard 1965), the timing of courtship tivity for 14 ducklings,pets. obs.). Six ducklingswere and pair formation for thesespecies is poorly docu- identified by the unique pattern of down and feathers mented.In theseregions, the timing of pair formation on their heads and bodies. may be influencedby variable or irregular breeding Male courtshipactivity.--In general,male courtship seasonsand the lack of seasonalor molt migrations of ducklingswas similar to male courtshipof adult (McKinney 1985, Oring and Saylet in press).In sev- females (Johnsgard1965; pets. obs.). Males directed eral SouthAmerican species, including the migratory four courtshipdisplays at ducklings (Rakoo,Display Chiloe Wigeon (Anassibilatrix), courtship activity has Shake, Grunt-whistle,and Preen-behind-the-wing; been noted before the end of the breeding season Johnsgard1965, Brewer 1990) and performed Pre- (Weller 1968),but the significanceof this exception- copulatory Head-pumping (Johnsgard 1965) near ally early courtship is unknown. I found that un- them. Group flightswith I-2 juvenile femalesand 2- pairedmales court and form bondswith ducklingsas 8 adult males,similar to courtshipflights described part of a pair formationprocess in Chiloe Wigeon. I for adult American Wigeon (Anasamericana; Wishart know of no previous descriptionsof this behavior in 1983),occurred late in the study period. I identified any waterfowl species. the intendedreceiver of a displayby noting the body Courtshipof ducklingswas discoveredincidentally orientationof the performer(McKinney in press),and during a study of biparental care in Chiloe Wigeon I considerhere only thosedisplays that were unam- (Decemberthrough February, 1985-1988;total 500 h biguouslydirected at ducklings(60 displayswere di- of observation)at five locationsin southernArgentina rectedat paired females;no unpaired femaleswere within 70 km of San Carlos de Bariloche (41ø08'S, present). 71ø15'W)and one location in BuenosAires province For 12 known-agebroods, the age at which duck- (38ø51'S,60ø05'W). Although similar trends in court- lings were first courtedranged from 9 days(class Ib) ship were observedat all six areas,I focusedon data to 33 days (classIIa) (mean [+SD] = 21 + 6.6). The from the three main study areasin southernArgen- number of displayingmales at one locationranged tina: Laguna Los Juncos,Estancia San Ramon, and from oneto 23,with up to sevenmales simultaneously Arroyo Pilcaniyeu (locationsand characteristicsfur- courting one or more ducklings. No male parents ther describedin McKinney and Brewer 1989). Fam- courtedtheir own ducklings,although mostpairs ac- ilies or courting maleswith ducklingswere observed companiedthem until ducklingswere at least6 weeks during 30- to 60-min periodsat all timesof day using old. Male ducklingsor juvenilesdid not courtfemales focal animal sampling (Altmann 1974) to record be- during the study period. havioral interactions and the activities of males, fe- Almostall courtshipdirected at ducklings(2,800 of males,and ducklingsevery 30 s. I observedcourtship 2,810displays) was performedby adult malesjudged during 14 days (45 h of observation)at EstanciaSan to be unpaired becausethey did not associatewith Ramon,35 days(102 h) at Arroyo Pilcaniyeu, 19 days an adult female for at least I h or exhibit behavior (22 h) at Languna Los Juncos,and 25 days (22 h) at seen when pairs are separated.(Courtship of duck- the other three locations. lings did not startuntil after mostbroods had hatched, Although individuals were not marked, all 28 pairs and it was very unlikely that paired maleswould be of parents and their broods, 15 courting males, and away from their own matesfor such long periods.) 6 eight-week-old ducklings were identified consis- These males increasedas a proportion of the local tently by morphologicalfeatures.