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The Auk 118(2):404-411, 2001

LEK-LIKE SYSTEM OF THE MONOGAMOUS BLUE-BLACK GRASSQUIT

JULIANA B. ALMEIDA1'3 AND REGINA H. MACEDOTM •Departamentode Ecologia,Universidade de Brasilia,70910-900 Brasilia, Brazil; and 2Departamentode Zoologia,Universidade de Brasilia, 70910-900 Brasflia, Brazil

ABSTRACT.--Inthis study, we investigatedthe role of and mating systemof the little known NeotropicalBlue-black Grassquit (Volatinia jacarina). Males form aggregations and executea highly conspicuousdisplay, resembling traditional leks. Number of displaying malesdeclined throughout the study period, thoughdisplaying intensity during the season showedno variation. Individual maleshad significantlydifferent displayingrates and also defendedterritories of very different sizes,ranging from 13.0 to 72.5 m2, but we found no associationbetween sizes and the averagedisplaying ratesof the residentmales. There alsois no associationbetween displaying rates of malesand size and vegetationstruc- ture of their territories. Four of seven nests were found within male territories and obser- vationsindicated that both sexesinvest equally in caring for nestlings.Results suggest that the Blue-blackGrassquit does not fit into the traditionallek ,contrary to what hasbeen proposed in the scarceliterature available. However, it is clearthat theseapparently monogamousbirds behavelike a lekking species.We speculateabout the possibilitythat aggregationof nesting territoriesin this speciesmay be due to sexualselection pressures, and suggestthat the Blue-blackGrassquit may be an ideal candidateto test Wagner's(1997) hidden-lek hypothesis.Received 2 August1999, accepted17 October2000.

SEXUALSELECTION in lekking species has and 1979), females do not nest within been the object of much attention during the male territories,but may dependupon resourc- last decades.A lek can be broadly defined as es within them. It is possiblethat in somespe- any aggregationof malesvisited by femalesfor cies, male aggregationsfunction like typical mating purposes(see review in Ht•glund and leks: individuals form a monogamouspair Alatalo 1995). Lek mating systems--where bondwhile displayingin a lek closeto thenest- males are clustered but still maintain fairly ing site (Ht•glund and Alatalo 1995). large territories--are sometimescalled explod- In this study,we addressedquestions related ed leks (Emlen and Oring 1977), as opposedto to the lek-like mating systemand functionof classicalleks, where malesare tightly clumped. the conspicuousdisplay exhibitedby a little- Males may chooseto display at sitesassociated studied,small, Neotropical , the Blue-black with resourcesused by females.For example, Grassquit (Volatiniajacarina). This common epaulatedbats court femalesfrom within ter- specieshas a geographicalrange extending ritories with resources females need, but do not from Mexico throughoutmost of SouthAmer- controlaccess to theseresources as a way to ob- ica. It typically occursin open savannagrass- tain females (Bradbury 1981, 1985). In cases where resources are located within male terri- lands,usually involvingsome degree of human disturbance.During the breeding season,adult tories,it is possiblethat femalechoice is based males are easily distinguishedfrom brownish upon the quality of resources,and not upon quality of the male. Thus, differencebetween a females and juveniles by their glossy black lekking speciesand one with territorial polyg- and white wing underparts.They yny may be difficult to discern,for in certain are easily spottedin the field due to their dis- species,such as some (Stiles tinctivedisplay, which consists of repeatedver- tical flights of about 50 cm, from elevated perches.During theseshort vertical flights, the 3Present address: Ecology, Evolution and Conser- vation BiologyProgram/314, University of Nevada, males exposethe white underwing area and Reno, Nevada 89557-0013,USA. E-mail: jaimeida@ emit a shortbuzzing vocalization("teez-wee"). unr. nevada.edu Males are generally found executingtheir dis- 4Address correspondenceto this author.E-mail: playsin a clusteredmanner, quite similarin ap- [email protected] pearanceto leks.

4O4 April 2001] Matingand Displays in Grassquits 405

Very little information is available concern- surementsof each individual (weight; and bill, tar- ing the Blue-blackGrassquit's mating systemor sus,right wing, and tail lengths). Behavioral observations.--Observations were con- the males' attention-callingdisplay. A descrip- ducted between the second week of November and tion of the display is provided by Sick (1997), third week of April, almostalways between 0600 and and early observationssuggested that the dis- 1100h (GMT-3 h). After this time period, displaying play could be related to pair formation (Alder- activity markedly declined until late afternoon, ton 1963). Some experimental work concerning when displayingresumed in a more subduedform. the acousticpart of the display was done by Observations were made with binoculars, at distanc- Wilczynski et al. (1989). The display rate is ap- es ranging from 15 to 20 m from grassquits,which proximately12 to 14 leapsper minute (Carval- did not disturb their displaying. Display perches ho 1957) at a speed of 1.13 m/s (Weathers used by males were marked with an identifying tag 1986). On the basis of very short field obser- to allow the demarcation of territorial boundaries. vations (3-4 days), Murray (1982) and Webber Other observationsincluded agonisticdominance in- teractions among males, feeding, courtship, and (1985) suggestedthat the Blue-blackGrassquit nesting. Three categoriesof were con- had a lek mating system,solely on the basisof sidered: (1) visitation, which is the number of times the fact that males display in aggregations. the adult entered the nest; (2) permanence,which is Bradbury (1977, 1981, 1985) specified four the time the adult spentinside the nest;and (3) prox- criteria for distinguishing traditional lekking imity, which is the time the adult spentwithin a 2 m speciesfrom those using alternative lek-like radius of the nest. Observations also included 5 min mating systems.These criteria are: (1) no pa- focalsamples of bandedmales to recordthe number ternal care; (2) the aggregationof males in an of display leaps executed(at least two samplesper arena, to which females come for mating; (3) male). To analyze how number of displaying males the arena contains no resources for females varied within the breeding season,we calculated a display sightingrate, that is, the number of displays other than the males themselves(e.g. no food, countedin a week divided by the total time spent in nesting sites, water, etc.); and (4) females are the field that week (number of displays divided by free to choosea mate when visiting the arena. sum of minutes in the field). That rate reflects the fre- In this study we analyzed male territorial dis- quency with which grassquitswere encounteredin persion, habitat preferences,and nesting be- display,because the time spentin the field involved havior of the Blue-blackGrassquit to see how both focal observationsand time spentsearching for well Bradbury's(1977, 1981, 1985) criteria for individuals. A different measure assessed the vari- characterizinglekking behaviorwere satisfied. ation in intensity with which males displayedalong the season,and that was calculatedby taking into ac- countonly the 5 min focalperiods, disregarding time METHODS spent between focal observations(number of dis- plays divided by sum of minutes of focal observa- Study site and generalmethods.•Our study took tions). We also registered the causesof display inter- placeat an experimentalfarm belongingto the Univ- ruption, which could be due to factors considered ersidadede Brasflia(Fazenda •gua Limpa)located neutral, suchas leaving the territory without appar- approximately30 km from Brasfiia,Brazil (15ø56'S ent reason and interruption by external elements and 47ø55'W). The study site comprised an area of (suchas carsor people on the road), or agonisticfac- typical "cerrado" vegetation,which varied from a tors, suchas the intrusion of other males.Displaying low savannagrassland sparsely covered with bushes maleswere occasionallyinterrupted by other males, to a denser form of "cerrado", consistingof grass- often causingthe resident to approachthe intruder land, bushes, and small trees. This area was divided and, sometimes,to pursue him. When a female ap- into a grid (100 x 50 m) of 50 quadrants of 100 m2 proacheda male,he continuedhis displaywhile get- each, with the 66 intersectionpoints marked with ting closer to the female. was only ob- identifying flags. The grid was boundedon one side servedonce because most of the time, after courtship by a dirt road, by a cultivatedarea on its secondside, was initiated, the pair flew to the ground beneaththe a small cliff on the third side,and shrubbygrassland vegetationand was lost to sight. on the fourth side. Vegetationstructure and resource availability.--We as- The study was conductedwithin the rainy season, sessedlocal vegetationstructure, which could be as- from September1995 to April 1996. From mid-No- sociatedwith suitability of the area for nesting,and vember 1995 until early April 1996, we captured 66 also availability of food (grasslandseeds) in territo- male and 38 female grassquitswith mist netswithin ries identified within the grid. That was done by ex- the study plot, marked them with unique combina- tending two perpendicular tapelines within each tions of coloredplastic bands, and took severalmea- grid quadrant, producing four identical 25 m2 406 ALMEIDAAND MACEDO [Auk, Vol. 118

14 TABLE1. Average display rates, agonisticinterrup- tions,and territory sizesof Volatiniajacarina males. 12 Average Agonistic Territory displays interruptions size 10 Male per minute per minute (m2)

ß ß M1 4.8 0.1 72.5 M2 5.2 0.1 51.0 M3 7.2 0.1 49.0 M4 8.0 0.2 -- M5 3.4 0.1 21.0 M6 6.2 0.0 -- M7 6.4 0.1 36.0 M8 10.8 0.1 39.0 M9 9.3 0.0 61.5 M10 6.1 0.0 55.0 0 i i i Mll 12.3 0.0 34.0 M12 5.7 0.1 -- 1 2 3 4 5 6 7 M13 1.8 0.0 -- Weeks M14 -- -- 22.0 M15 -- -- 13.0 FIG. 1. Weekly variation in the intensity (solidcir- M16 -- -- 46.5 cles)and sightings(open circles) of displaysin Blue- black Grassquits.Weeks in 1996:1 = 5 to 11 Febru- ary; 2 = 12 to 18 February;3 = 26 to 29 February;4 = 11 to 17 March; 5 = 18 to 24 Marcl•; 6 = 25 to 31 perchesusually were tree branchesor shrubs March; 7 = 1 to 7 April. locatedwell abovethe surroundinggrassland vegetation.Display activity initiated at around 0600 h (averageof 8 displaysper rain), peaked squares.Along the tapeline we determinedthe per- at 0945 h (averageof 11 displaysper min) and centcover of differenttypes of substrate:(1) exposed practicallyceased by 1100h (lessthan 1 display soil; (2) herbaceous(excluding savanna grassland); per min; countstaken during 17 days). (3) "campo sujo" (savannagrassland sparsely cov- There was a significantnegative relationship ered with bushes);(4) tall savannagrassland (>30 betweenthe display sightingrate with regard cm); and (5) low savannagrassland (<30 cm). Thus, to the weeks of observation (r =-0.87, n = 7 each25 m 2square had the vegetationalong two of its weeks, P = 0.012;Fig. 1), indicatingthat fewer sidesassessed. With that we extrapolatedthe percent grassquitswere displaying as the seasonpro- of eachvegetation type for each25 m 2square. To de- termine the percent cover of each vegetationtype gressed.On the other hand, intensity of dis- within territories,we multiplied the percentagesof plays did not vary with the season(r = 0.03, n each vegetation type by the area each respective = 7 weeks, P = 0.95), even when leaving out squareoccupied within a territory. For comparison week 6, where only one display sighting oc- purposes, areas of each vegetationcategory within curred (r = 0.58, n = 6 weeks,P = 0.23;Fig. 1). territorieswere convertedto percent of territory. A total of 13 individuals were observed with- in the grid for at leasttwo, 5 min focal samples. RESULTS A one-way ANOVA was used to compare the displaying rates (number of displaysper rain) Displayseasonality, individual rates, and inter- among these individuals. Averagedisplaying ruptions.--Thefirst sightingof grassquitsin the rates were significantly different between study area occurred on 30 September1995, males (F = 4.38, df = 12 and 95, P < 0.001; Ta- when we observed three males, only one of ble 1). During the 5 min focal observationsof which had already acquireda completeblack these males, display interruptionscaused by . On 4 October 1995, we observeda intruding males were also noted. A one-way group of 15 individuals; however,it was not ANOVA showedthat the number of interrup- until mid-December,after the rainy seasonwas tions per minute did not vary significantly well underway, that we observeddisplaying amongthese individuals (F -- 1.35,df = 12 and males.By the end of December,a large number 95, P = 0.20; Table 1). of displaying males occurredwithin the study Territorysize and quality.--We identified 12 plot, sometimesseparated by only2 m. Display territorieswithin the grid area,9 of which were April 2001] Matingand Displays in Grassquits 407

L $ I H G F E D C B A 6

lorn

FIG.2. Locationof territorieswithin the studygrid. Territories,identified by the malecodes (see Table 1) are in continuousblack or brokenlines; broken lines indicatespatial overlap. of focalmales (Table 1 and Fig. 2). Territorysiz- There was no significant correlationbetween es varied from 13.0 to 72.5 mL Individual males territory sizesand the averagedisplaying rates did not defend their territoriesthroughout all of their residents(r = -0.094, n = 9, P = 0.805). of the weeks of the study, but remained for Within the grid, we comparedthe vegetation varying periods ranging from three to 22 structureof the 25 m= squaresthat overlapped weeks; two males were present for more than with grassquit territories (n = 89 squares, four months (Fig. 3). The territorieswere clus- mainly betweenlines one and three of the grid) tered betweenlines one and three of the grid, with thosewithout overlappingterritories (n = whereaswithin other grid areas,even encoun- 111, mainly between lines three and six of the tering a grassquit was a rare event (Fig. 2). grid; Fig. 2). We found a significantdifference for the followingvegetation categories: low sa- MI6 I vanna grassland(Mann-Whitney U-test: U = M15 5,963.5,P = 0.011);tall savannagrassland (U = MI4 1 1,900.0, P < 0.001); and herbaceous (U = Mll ll 6,874.0,P < 0.001; Fig. 2). The greatestdiffer-

M10 ll encefound was for the percentageof tall sa-

M9 vannagrassland which, in the areaoccupied by

M8 ll the , accountedfor 45% of ground cover,

M7 ll as opposedto only 14%in the unoccupiedarea.

M5 With a multiple-regressiontest, we also ex-

M3 amined the possibility of an associationbe-

M2 tween displayingrate of a territorial male, and

M1 size and vegetationstructure of his territory, but found no significantrelation among these 123412341234123412341234 variables. Nov Dee JanDate Feb Mar Apr Nestingand parentalinvestment.--Seven nests Fxc. 3. Territorial occupationfrom the day each were found during the study period (four with- male was banded until the last day observationsoc- in the grid) in different nestingstages; four of curred (codes as in Table 1). the nestswere observed for periodsthat ranged 408 ALMEIDA AND MACEDO [Auk, Vol. 118 from 3.5 to 12.5 h. In three of these nests, ob- cuted to augmentthe radius of vocalizationre- servations were conducted on a single day ception by other individuals. In our study, (from 3.5 to 5.5 h). In one nest, observationsto- however, perches used by the grassquits taling 12.5 h were spread out over five days. emergedabove the surroundinggrassland veg- Nests are small (diameter approximately 7.5 etation, and displaying males were visible cm) and round, composedmostly of roots,and when resting,but becamemore conspicuousto are attachedto the herbaceousvegetation from us when they executed their displays. It is 10 to 50 cm off the ground.In five of the nests, probable that both the visual and auditory two nestlingswere present.The other two nests componentsof the display are important to in- had onesingle , which had apparentlybeen creaseperception by otherindividuals. deserted.We comparedmale and female pa- Grassquitshad their peak displayactivity in rental investment in the number of visits, time the morning, as is commonfor many other spent within (minutesper hour), and in the birds. The reasonsfor this appear to vary de- proximity of the nest.There was no difference pendingupon the species.Birkhead and Moller in male and femaleparental behavior for any of (1992) suggestthat male singingin the morn- the categoriesmeasured (n = 4 nests):(1) av- ing is relatedto greaterfemale fertility during eragenumber of visits (per hour) for males= this time period, and that singingcould func- 2.06 + SD of 1.72,average number of visits (per tion as a pair-guarding mechanismwhile si- hour) for females = 1.22 ___0.70: t = 0.912, df = multaneouslyattracting other females for cop- 3, P = 0.429; (2) averagepermanence (minutes ulation. In a study of Chiffchaffs(Philloscopus per hour) in the nest for males = 1.40 + 0.62, collybita),Rodrigues (1996) argued that early averagepermanence (minutes per hour) in the morningsinging could be usedby malesto de- nest for females = 4.84 +_ 8.12: t =-0.88, df = termine whether females have survived in- 3, P = 0.442;and (3) averagetime (minutesper creasedpredation risk imposedby nighttime, hour) near the nest for males = 6.66 _+8.11, av- and could facilitateacquisition of a new mate eragetime near (minutesper hour) the nestfor when does occur.To determinerea- females = 11.12 __+9.98: t =-7.68, df = 3, P -- sonsfor the peakin earlymorning display with 0.192. In two nests, the male parents were somedegree of certaintyfor Blue-blackGrass- banded. This allowed us to examine the rela- quits,it would be necessaryto pinpointthe fe- tion between their displaying activities and males' fertile period. The gradual decreasein nesting. In nest #1, found on 30 January1996 displaying throughoutthe seasonreveals that with two nestlings,the male parent (M5) was that activity is moreimportant in thebeginning observedexecuting displays from the second of the seasonwhen males are establishingter- week of November until the fourth week of ritories and determining dominance hierar- March. In nest #7, found on 17 April 1996,dis- chies.On the other hand, display intensity did playing by male M9 lasted from the fourth not vary throughoutthe season,and different week of Januaryto the end of April. males occupiedthe area for varying periods. Consequently,there appearsto be someasyn- DISCUSSION chronousbreeding in the population,possibly allowing malesexcluded from the area in the The role of the Blue-blackGrassquit male dis- initial part of the seasonto obtaincopulations. play may be assessedby analyzingthe context Forsong birds, male competitionfor territory in which it occursand its variation throughout acquisition occurs mostly through singing the day and breedingseason. Wilczynski et al. (Krebs 1977, Krebs et al. 1978, Westcott1992). (1989)proposed that the aerial part of the dis- The intensity, frequency,and quality of the play (i.e. the leap itself) is not associatedwith songare associatedwith territorialparameters, visual conspicuousness,because in their study such as size, resourcequality, or both; addi- the grassquitsused perches lower than the sur- tionally,the physicalcondition and age of the rounding vegetation.Thus, they reasonedthat individual will also affect song components the leap would be visible only to nearby indi- (Westneat1988, Dale and Slagsvoid1990, West- viduals. On the basis of experimentswith vo- cott 1992, Chapman and Kramer 1996). Terri- calizationsbroadcast from speakersat various torial intrusionsare frequentlyexecuted by in- heights,they concludedthat the leap was exe- dividuals occupyinglower quality territories April 2001] Matingand Displays in Grassquits 409

(Matthysen 1990) or by satellite males without Lack of difference in vegetation structure territories (Smith 1978, Westcott 1992). The among territories implies that females are not greatercapture rate of grassquitmales in that choosingamong males on the basisof resource study and Webber's(1985) observation of a 10: parameters.Although femaleswere seen only 1 ratio of males to femalesin the field support with territorial males, thus excludingpart of the idea that the display area is occupiedby a the male population,characteristics other than small percentage of the male population, territorial onesmust be important in determin- whereas many more transient males occur in ing female choice.The expressivepaternal in- the area. vestmentfound may be crucialfor offspringde- Territories vary greatly in size, the largest velopmentand survival, thus limiting female one more than five times the size of the smallest reproductive success.In this case, females one. However, even the largest territory (72.5 would benefitgreatly by being ableto evaluate m2) is exceptionallysmall by most standards. a male'spaternal-care potential. This doesnot Territoriesare unmistakablyused only for re- excludeother phenotypictraits that could be productive purposes--given their diminutive indicativeof overall male quality. sizes,the factthat grassquitswere seldomseen The small territory sizesassociated with con- feeding within them, and that territorial dis- spicuous displays prompted Murray (1982) playspractically ceased at the end of February. and Webber (1985) to consider a lek-mating Within the grid area, grassquitsonly occu- system for the Blue-black Grassquit. In leks, pied areaswith tall savannagrassland, com- males aggregateand display in a given area pletely ignoring the remainingavailable space. and, typically,territories are very small (West- Because some of the nests found were within cott 1992, Andersson1994, HOglund and Ala- territories in the grid, it is possiblethat this talo 1995). Becauseaggregations of type of vegetationis an importantdeterminant may occurfor reasonsother than mating (Ber- of quality in the form of adequatenesting sites. tram 1978,Danchin and Wagner 1997), specific Other more subtle habitat characteristics not criteria have been suggestedto define leks measuredin this study may alsobe important. (Bradbury 1977, 1981, 1985), the most relevant However, there is no relation between display of which are that males do not participate in rate of individuals with the size or specificveg- caringfor offspring,and that the lekking arena etation structure of territories, or both, nor is containsno resourcesneeded by females.In ef- there any difference in vegetation structure fect, upon visiting a lekking arena, females among territories. Hence, females do not must choose a mate on the basis of factors other choose males on the basis of individual terri- than territory quality and paternal care (HOg- tory characteristics.However, territories are es- lund 1989, Westcott 1992, Andersson 1994, tablished only within areas with appropriate Johnsgard1994, Prum et al. 1996). Male traits vegetationcharacteristics, which may limit the that may be used in female choiceare not lim- numberof malesoccupying a given region. ited to plumage or size, for example,but may Female choice may be the result of male- be acoustic or behavioral characters as well. male competition(passive choice), or it may oc- In Blue-blackGrassquits, despite male ag- cur throughactive selectionof somemale char- gregationsbeing very similar in form to lekk- acteristic (Halliday 1983, O'Donald 1983, ing arenas,other characteristics lead us to con- and Halliday 1984). Benefits result- clude that their mating systemis not that of a ing from female choicemay be direct (e.g. ter- typical lek. Females,at least in the casesmon- ritorial resourcessuch as food or nestingsites); itored within the grid, build their nestswithin or indirect, involving geneticquality that will male territories; additionally, some and per- produce attractive and viable offspring (An- haps all males exert parental care. We do not dersson 1994, Moller and Thornhill 1998). The have substantial data to determine whether evidencefrom Blue-blackGrassquits points to males typically continueto display after nest variabletypes of benefitsthat can be gainedby initiation, or whether they dedicate all their femalesthrough their choice:nesting site, pa- time and energy to the nesting attempt.In two ternal care, and, possibly,genetic quality for nests,display activitieswere carried out well offspring.In addition to mate attraction,males before, during, and after nesting activitiesoc- may also use displays in territorial defense. curred. Although males had significantlydif- 410 ALMEIDAAND MACEDO [Auk, Vol. 118 ferent display rates, the number of interrup- male displays,EPCs, paternal investment,and tions by intruding malesdid not differ among certaintyof paternity. focal males. Thus, displayscan function to at- tract additional copulationsfor males,but that ACKNOWLEDGMENTS doesnot rule out the possibilitythat malesmay use displaysin territory maintenance. For their good-naturedhelp in the field we thank In specieswhere food, nestingsites, or egg- Mauricio Sacramento, Adriana Pinto, Gustavo Ott, Carlos Bianchi, and Celine Melo. We thank Richard laying sitesare locatedwithin male territories, Wagner,Bette Loiselle, and two anonymousreview- lek systemssimply do not apply (H6glund and ers for their thoroughrevision of an earlier version Alatalo 1995).There are other examplesof spe- of the manuscript.Insightful commentswere pro- cies showing complex mating strategiesthat vided by RobertoCavalcanti, Guarino Colli, and Su- defy a clearcutdefinition. In coloniallynesting san Haig. Financial assistancewas granted by Bra- Razorbills (Alca torda),a traditionally zil's Conselho Nacional de Desenvolvimento viewed as monogamouswith biparental care, Cientifico e Tecno16gico(CNPq) in the form of a both sexesattend mating arenasto obtain ex- scholarshipfor J.B.A.and a ResearchFellowship for trapair copulations(EPCs) (Wagner1992). R.H.M. Wagner (1997) proposedthe hidden-lek hy- pothesisto explain how territorial clustering LITERATURE CITED could evolvein monogamousbirds. In essence, ALDERTON,C. C. 1963.The breedingbehavior of the a hidden lek could operatebecause in monog- Blue-blackGrassquit. Condor 65:154-162. amousspecies, only a singlefemale pairs with ANDERSSON, M. 1994. . Princeton the highestquality male within a certainarea. University Press,Princeton, New Jersey. However, other femalescan attempt to obtain BERTRAM,B.C. R. 1978.Living in groups:Predators EPCs from this high-quality male. This would and prey. Pages64-96 in BehaviouralEcology (J. lead to a clusteringof territories becausefe- R. Krebs and N. B. Davies, Eds.). Blackwell Sci- maleswould prefer to sociallypair with those entific Publications, Oxford. males whose territories provided them with BIRKHEAD,T. R., AND A. P. MOLLER.1992. Sperm easieraccess to the high qualitymale. Although Competitionin Birds: EvolutionaryCauses and Consequences.Academic Press, San Diego, a lossof paternity couldensue for thesemales, California. this would still be better than not gaining a BRADBURY,J. W. 1977. Lek mating behavior in the breedingpartner. hammerheadedbat. Zeitschriftffir Tierpsychol- Thus, the hidden-lek hypothesis predicts ogie 45:225-255. that aggregationsin monogamousbirds may BRADBURY,J. W. 1981. The evolutionof leks. Pages occurthrough sexualselection. Although Blue- 138-169 in Natural Selection and Social Behav- black Grassquitterritories are highly clumped, iour (R. D. Alexander and D. W. Tinkle, Eds.). in our study site unoccupiedareas were com- Chiron Press, New York. posedof differentvegetation. However, within BRADBURY,J. W. 1985. Contrasts between and the occupied area territories were homoge- vertebratesin the evolutionof male display,fe- neous for characteristics evaluated. Thus, it is male choice and lek mating. Fortschritte der Zoologie 31:273-289. unclearfrom this systemhow muchaggregated CARVALHO,C. T. 1957. Notas ecol6gicassobre Vola- territories may be the result of habitat con- tinia jacarina(Passeres, Fringillidae). Boletim do straints versus lek mechanisms. Museu Paraense Emilio Goeldi 2:1-10. Nonetheless,existence of pair bonds and pa- CHAPMAN, M. R., AND D. L. KRAMER. 1996. Guarded ternalcare in Blue-blackGrassquits is surprising resources: The effect of intruder number on the consideringthe energy-consuming and conspic- tactics and success of defenders and intruders. uous display of males in aggregations,which Behaviour 52:83-94. leads to the suspicionthat EPCs may occur. DALE, S., AND T. SLAGSVOLD. 1990. Random settle- Shouldthat be the case,it wouldbe enlightening ment of Pied Flycatchers,Ficedula hipoleuca: Sig- nificanceof male territory size. Animal Behav- to identify whethermore attractivemales obtain iour 39:231-243. a greater proportion of EPCs, a situationap- DANCHIN, E., AND R. H. WAGNER. 1997. The evolu- proachingthe hidden-lekhypothesis. Addition- tion of coloniality:The emergenceof new per- ally, this speciesprovides promising circum- spectives.Trends in Ecologyand Evolution12: stancesin which to exploreinterplay between 342-347. April 2001] Matingand Displays in Grassquits 411

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