July2000] ShortCommunications 799

sonIII, andtwo anonymousreviewers. Funding was L. S. Hall, S. K. Robinson, S. I. Rothstein, D. C providedby theGlobal Climate Change program of Hahn, and T. D. Rich,Eds.). Studies in Avian Bi- theU.S. Fish and Wildlife Service, the BBIRD pro- ology No. 18. gramof theU.S. Geological Survey, the National Fish GOGUEN,C. B.,AND N. E.MATHEWS. 2000. Local gra- andWildlife Foundation, and the University of Wis- dientsof cowbirdabundance and parasitism rel- consin at Madison. ative to livestockgrazing in a western land- scape.Conservation Biology 14: in press. LITERATURE CITED GUSTAFSON,E. J., AND t. R. CROW.1994. Modeling the effectsof forestharvesting on landscape COKER,D. R.,AND D. E. CAPEIN.1995. Landscape-lev- structureand the spatialdistribution of cowbird el habitat use by Brown-headedCowbirds in parasitism.Landscape Ecology 9:237-248. Vermont.Journal of Wildlife Management59: MAYFIELD, H. E 1965. The Brown-headed Cowbird 631-637. with old andnew hosts. Living Bird 4:13-28. FINCH,D. M. 1991.Population ecology, habitat re- ORTEGA,C. P.1998. Cowbirds and other brood par- quirements,and conservation of Neotropicalmi- asites.University of Arizona Press,Tucson. gratory birds. United StatesForest Service Gen- RAIM, A. 1987. A radio transmitter attachment for eral TechnicalReport RM-205. smallpasserine birds. Bird-Banding 49:326-332. FRIEDMANN,H. 1929.The cowbirds:A studyin the ROBINSON,S. K., S. I. ROTHSTEIN,M. C. BRITTING- biologyof socialparasitism. C. Thomas,Spring- HAM, L. J. PEtit, AND J. g. GRZYBOWSKI.1995. field, Illinois. Ecologyand behavior of cowbirdsand their im- GATES,J. E., AND D. R. EVANS.1998. Cowbirds breed- pacton host populations. Pages 428-460 in Ecol- ing in the centralAppalachians: Spatial and ogyand management of Neotropicalmigratory temporalpatterns and habitat selection. Ecolog- birds: A synthesisand review of critical issues ical Applications8:27-40. (T. E. Martin and D. M. Finch,Eds.). Oxford Uni- GOGUEN,C. B. 1999. Brown-headed Cowbird move- versity Press,New York. ments,habitat use, and impactson hostsin a ROTHSTEIN,S. I., J. VERNER,AND E. STEVENS.1984. grazedand ungrazedlandscape. Ph.D. disser- Radio-trackingconfirms a uniquediurnal pat- tation, University of Wisconsin,Madison. ternof spatialoccurrence in theparasitic Brown- GOGUEN,C. B.,AND N. E. MATHEWS.1998. Songbird headedCowbird. Ecology 65:77-88. communitycomposition and nestingsuccess in THOMPSON,E R. III. 1994.Temporal and spatial pat- grazedand ungrazedpinyon-juniper woodlands. terns of breeding Brown-headedCowbirds in Journalof WildlifeManagement. 62:474-484. the midwestern United States.Auk 111:979-990. GOGUEN,C. B., AND N. E. MATHEWS.1999. Review of VERNER,J., AND L. V. RITTER. 1983. Current status of the causesand implicationsof the association the Brown-headed Cowbird in the Sierra Nation- betweencowbirds and livestock. Pages 10-17 in al Forest. Auk 100:355-368. Researchand management of theBrown-headed Received26 February1999, accepted 24 November1999. Cowbirdin westernlandscapes (M. L. Morrison, Associate Editor: S. I. Rothstein

TheAuk 117(3):799-802,2000

FemaleDominance and Aggressive Behaviors in HouseSparrow Flocks JODIEM. JAWOR• BiologyDepartment, Ball State University, Muncie, Indiana 47306, USA

Somebird speciesdisplay intersexual dominance male dominance,year-round male dominance,and at foodresources (e.g. Bekoff and Scott 1989, Piper alternatingdominance wherein females dominate in and Wiley 1989,Tarvin and Woolfenden1997). Such thebreeding season and males in thenonbreeding interactionsfall into threepatterns: year-round fe- season(Smith 19'80). Although Smith found alter- natingdominance to be themost common pattern in birds,she suggested that year-roundfemale domi- • Presentaddress: Department of Biology,Univer- nanceshould occur in sociallymonogamous, non- sity of Dayton, 300 CollegePark, Dayton,Ohio territorialspecies. In suchspecies, no advantage 45469,USA. E-mail:[email protected] would accrue to males who exhibit dominance in the 800 ShortCommunications [Auk, Vol. 117 nonbreedingseason in preparationfor territory ac- TABLE 1. Number and outcome of intersexual in- quisitionfor the breedingseason. teractionsinitiated by House Sparrowsat three House Sparrows(Passer domesticus) are socially feedersand at threelevels of aggression. monogamousand defend only small territories Number won Number not around their nest cavities(Lowther and Cink 1992). Initiator (%) won (%) Total This makesthem a candidatefor year-roundfemale dominance.Dominance relationships in HouseSpar- Feeder One rowshave been investigated with conflictingresults. Male 48 (66) 25 (34) 73 Watson (1970) found that males in small captive Female 90 (79) 24 (21) 114 flockswere dominant year-round, whereas Kalinoski Feeder Two (1975)noted that femaleswere dominantonly dur- Male 105 (56) 84 (44) 189 ing winter.Cink (1977),working with free-ranging Female 179 (75) 61 (25) 240 flocks,found that maleswere dominantduring the Feeder Three nonbreedingseason and femalesduring the breed- Male 97 (70) 42 (30) 139 ing season.Hegner and Wingfield (1987) found that Female 101 (82) 22 (18) 123 femalesin small captive flockswere dominant dur- ing the nonbreedingseason, but neither sex was Low-level aggression dominantduring the breedingseason. Finally, a re- Male 32 (42) 44 (58) 76 cent summaryof dominancepatterns in HouseSpar- Female 73 (72) 28 (28) 101 rows concludedthat femalesare dominant during Mid-level aggression springand summerand males during fall and winter Male 132 (72) 52 (28) 184 (Lowtherand Cink 1992).Because the claim of alter- Female 202 (80) 51 (20) 253 nating dominancein House Sparrowsis in opposi- High-level aggression tion to the patternthat would be predictedby Smith Male 86 (61) 55 (39) 141 (1980), I addressedsex-biased dominance in winter Female 95 (77) 28 (23) 123 interactionsof free-ranging flocks of House Spar- rows. Methods.--I observed interactions at three feeders durinõ the winter (Novemberto February)of 1997- aggression(see Summers-Smith1963). Aggression 98 in Muncie, Indiana. Feederswere separatedby at levels were describedas low, mid, or high corre- least 3 km, and sparrowspresumably were from spondingto threats,lunges, and attacks,respective- threedifferent flocks (typical home ranões separated ly. An individualwas considered to havewon the in- by lessthan 2 km; Lowtherand Cink 1992).Winter teraction if it caused the other individual to leave the temperatureswere typical for southeasternIndiana, feeder. An individual was considered not to have althouõh snowfall was below averaõe(Ball State won the interaction(=no win) if the otherindividual WeatherStation). Thus, the interactionsI observed did not leavethe feeder,or if it displayedback at the likely werenormal for the studyarea. House Spar- initiator, who then left. I analyzedpatterns in inter- rows often use feedersin this area and may not be actionsusing chi-square tests, with eachinteraction adverselyaffected by snowcover when it occurs. consideredindependent of the others. I observed interactions for one hour in the morn- Results.--Overall, I observed 187, 429, and 262 in- inõs (one hour after sunrise)from a blind set near tersexual interactionsat the three feeders(Table 1). eachfeeder. I madeapproximately 27 h of observa- Females initiated more interactions with males than tion at feeder one, 25 h at feeder two, and 29 h at feed- vice versa at feeder one (X2 = 8.99, df = 1, P < 0.005) er three. Birds in the three flocks were not banded, and two (X2 = 6.06, df = 1, P < 0.025)but not at feed- but I assume the data at each feeder can be treated as er three (X2 = 0.98, df = 1, P > 0.10;Table 1). An in- an independent random sample for two reasons. dividual that initiated an interaction was likely to First, flockswere larõe, with approximately20 in- win that interaction,regardless of sex(initiator won dividuals(mean of pointcounts every 5 min) of each 71% of interactions).Females won moreof the inter- sex in each flock. Second,I frequently witnessed actionsthat they initiatedthan did malesat feeder multipleinteractions that involved different individ- two (X2 = 16.3,df = 1, P < 0.001)and three(X 2 = 4.73, uals. Thus, the data reportedhere are not attribut- df = 1, P = 0.029).The pattern also occurred at feed- able to a small number of individuals in each flock er one, but the differencewas not significant(X 2 = but ratherreflect samplinõ from a varietyof individ- 3.35, df = 1, P = 0.067).Note, however,that the two uals of each sex in each flock. feeders where females won more interactions were For each intersexual interaction I recorded the sex not the same two feeders at which females initiated of the initiator, whether the initiator won the inter- more interactions(i.e. in no casewere data from one action,and the type of aõõressionused. House Spar- feederclearly "different" from thoseat theother two rows use three stereotypic aõõressivedisplays feeders). (threat,lunõe, and attack)that I usedto cateõorize Basedon the aboveresults, I pooleddata from the July2000] ShortCommunications 801 three feedersto ask questionsconcerning levels of populationsin Cink'sstudy occurred at higherlati- aggressionin interactionsinitiated by onesex or the tudesthan the populationthat I studiedand thus other.Both sexes used mid-level aggression most of- shouldhave had highersize dimorphism. Sexual di- ten (Table1). Males and females,however, differed morphismin northern House Sparrowsmay be in their use of the three levelsof aggression(X 2 = maintainedby severalfactors. First, smallerfemales 9.14, df = 2, P = 0.01). Females initiated low- and may havea reproductiveadvantage' over larger fe- mid-levelaggressive interactions disproportionately, malesby beingable to beginbreeding sooner (Down- whereasmales did so for high-levelaggression (low hower1976). Second, House Sparrows near the pop- vs. high, X2 = 4.24, df = 1, P = 0.039;mid vs. high, ulation mean size (small males and large females) X• = 8.01,df = 1, P = 0.005;Table 1), althoughonly experiencehigher amounts of interspecificcompeti- the mid vs. high comparisonwas significantafter tion and lower overwinter survival (Johnstonand Bonferroni correction. Fleischer1981). Third, smallerfemales may require When comparingfrequencies of initiatedinterac- lessenergy for daily survivalthan larger individuals tionswon at the threelevels of aggression,males did and maybe ableto easilymeet their energyrequire- not experienceconsistent frequencies (X • = 20.3, df ments(see Johnston and Fleischer1981). Smaller fe- = 2, P < 0.001). In particular maleslost more low- malesmay avoidinteractions that they are unlikely levelinteractions than mid- or high-levelinteractions to win owing to their size disadvantageand thus (low vs. mid, X• = 19.0, df = 1, P < 0.001; low vs. may be subordinateduring the winter in northern high, X2 = 6.36, df = 1, P = 0.01).Males lost similar populations. frequenciesof interactionsat mid- andhigh-level ag- Giventhese factors, I predictthat a gradientexists gression(X • = 3.70, df = 1, P = 0.054).Overall, males from year-roundfemale dominance in the climati- won 62% of the interactionsthey initiated.In con- cally milder southernlatitudes of the HouseSpar- trast, femaleswon similar frequenciesof interactions row'srange, to alternatingdominance in the climat- that theyinitiated at all threelevels of aggression(X 2 ically harshernorthern latitudes. Indeed, the same = 2.38, df = 2, P > 0.10) and won 78% of all inter- predictionholds for any nonterritorialsocially mo- actionsthey initiated. nogamousspecies with a broadlatitudinal range. Discussion.--Females were the dominant sex at During intersexualinteractions, both sexesused winterfood resources in thisstudy, as would be pre- mid-level(lunge) aggression preferentially. This is dictedby Smith (1980)but in contrastto Cink (1977). consistentwith the predictionsof Enquist(1985) and Smithcited several cases of specieswith knownyear- the findingsof Popp(1987) that displayingindivid- round female dominance that have a common link of uals use the level of aggressionthat is sufficientfor lowerprebreeding male dominance (compared with securingthe desiredresource without taking on ex- specieswith knownyear-round male dominance or cessive costs. Mid-level aggressionmay be more alternating dominance).Lower prebreedingmale costlythan low-levelaggression in termsof energy dominancemay be a result of lack of territorialbe- expenditureand the potentialfor retaliation,but it haviorduring the breeding and nonbreeding seasons may be moreeffective in demonstratingthe levelof in thesespecies. House Sparrows maintain only a risk an individual is willing to take to obtainor hold smallterritory around their nestsite and do not de- a resource(Enquist 1985). fend foragingterritories at any time. Thus, House With this in mind, displayingindividuals should Sparrowssatisfy a requirementfor exhibitingyear- makelittle useof expensivedisplays that potentially round femaledominance (Smith 1980). couldtrigger retaliation, such as high-level(attack) Cink (1977) found that female HouseSparrows aggression.Males in my study were more willing to weredominant during the breedingseason, the only use high-levelaggression than were females.Males studyof free-rangingflocks that has been conducted mayuse high-level aggression based on their need to at thattime of year.Other studies of HouseSparrows obtainresources. Popp (1987) found that individuals haveeither not addresseddominance relationships demonstratedhigher levels of aggressionbased on duringthe breedingseason, or havefound the sexes the importanceof the resourcein question.Subor- to be equallydominant in captivestudies during the dinateAmerican Goldfinches (Carduelis tristis) pref- breedingseason. By combiningthe findingsof Cink erentiallyused high-levelaggression against domi- (female breeding-seasondominance) and of my nant finches when the subordinates had been de- study (femalenonbreeding-season dominance), I ar- prived of food. FemaleHouse Sparrows may be able gue that femalesare dominant year-roundin the to enforcetheir dominanceto a point that malesbe- populationthat I studied. comedesperate for accessto the food resourceand Yet,discrepancies exist between the nonbreeding- resortto costlyhigh-level aggression to acquireit. seasonresults of Cink and mine. Severalfactors may Femaleswere as likely to win an interactionusing account for these differences. Sexual size dimor- low-level aggressionas using mid-level aggression. phismhas been reported in HouseSparrows, with an Why they usedmid-level aggression more often is increasein the extentof dimorphismat morenorth- not clear.I did not know agesof birds or numbersof ern latitudes(Johnston and Selander1973). All of the juvenileswithin flocks,and femalescould have used 802 ShortCommunications [Auk,Vol. 117 low-levelaggression against young males while em- variation in choice of behavior. Animal Behav- ploying mid-level aggressionagainst older males. iour 33:1152-1161. Both sexesused mid- and high-levelaggression HEGNER,R. E., AND J. C. WINGFIELD. 1987. Social sta- against a same-sexopponent preferentially (Jawor tus and circulatinglevels of hormonesin flocks 1998).This may indicate that separate dominance hi- of HouseSparrows, Passer domesticus. Ethology erarchies exist for the sexes, and for intersexual in- 76:1-14. teractions,and that differentstrategies exist for com- JACKSON,W. M. 1991.Why do winnerskeep win- petingwithin thesehierarchies, as has been observed ning?Behavioral Ecology and Sociobiology28: in otherspecies (e.g. Enoksson 1988, Bekoff and Scott 271-276. 1989, Lahti et al. 1996). JAWOR,J. M. 1998. Aggressive interactionsand be- Femaledominance also may accountfor the high haviors in House Sparrow (Passerdomesticus) frequency of male loss during male-initiated low- flocks.M.S. thesis,Ball StateUniversity, Muncie, level intersexual aggression.Low-level aggression Indiana. may not be an effectivedisplay for malesbecause fe- JOHNSTON, R. E, AND R. C. FLEISCHER.1981. Over- malesare unwilling to recognizeit asa threatto their winter mortality and sexual size dimorphismin dominancestatus. Another possibility is that males the HouseSparrow. Auk 98:503-511. uselow-level aggression against females that are the JOHNSTON,R. F., AND R. K. SELANDER.1973. Evolu- samesize or larger.In suchcases, a femaleshould not tion in the HouseSparrow. III. Variationin size respondto low-levelaggression by leavingthe feed- and sexualdimorphism in Europeand North er. One couldtest the hypothesisthat lossesin male- and South America. American Naturalist 107: initiated intersexualinteractions depend on the fe- 373-384. male's responseby examining male-male interac- KALINOSKI,g. 1975.Intra- and interspecificaggres- tions. Specifically,the initiator in male-maleinter- sion in House Finchesand House Sparrows. actions should win the interaction more often than Condor 77:375-384. not (seeJackson 1991). In any case,the questionof LAHTI, K., K. KOIVULA, M. ORELL, AND S. RYTKONEN. why malesuse a levelof aggressionin interactions 1996. Social dominance in free-living Willow that they often lose will be better answeredwith Tits Parus montanus: Determinants and some im- banded individuals of known size in flocks with plicationsof hierarchy.Ibis 138:539-544. known histories of interactions. LOWTHER,P. E., AND C. L. CINK. 1992. House Spar- Acknowledgments.--Ithank Randall Breitwisch, row (Passerdomesticus). In The birds of North Gary Dodson,Aaron Holbrook, and Keith Tarvin for America, no. 12 (A. Poole,E Stettenheimand E help with the researchand producingthe manu- Gill Eds.). Academyof Natural Sciences;Phila- script.I alsothank the people who let mewatch feed- delphia, and AmericanOrnithologists' Union, ersin theiryards, Wild BirdsUnlimited for donation Washington,D.C. of bird seed,and BetteLoiselle and two anonymous PIPER, W. H., AND R. H. WILEY. 1989. Correlates of reviewersfor suggestionson a previousdraft of the dominancein winter White-throatedSparrows: manuscript. Age, sexand location.Animal Behaviour37:298- 310.

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