Pushy males and choosy females:courtship disruption and mate choice in thelekking great snipe

Stein Are S×ther1*, Peder Fiske1,2 and John Atle KÔlÔs2

1Department of Zoology, Norwegian University of Science andTechnology, N-7491 Trondheim, Norway2Norwegian Institute for Nature Research,Tungasletta 2, N-7485 Trondheim, Norway

We studied the e¡ects of male disruptive behaviour on female mate choice and male mating success in thegreat snipe, Gallinago media, a lekking bird. Harassment from neighbouring males, a widespread beha-viour in lekking animals, was the most prevalent cause of females leaving a male territory. Several linesof evidence show that females did not prefer to mate with males able to protect them from harassment.Males that obtained mating success were no less likely to su¡er disruptions and females were no less likelyto be disrupted when with their preferred male. Females returned to the male they later mated with,despite being repeatedly chased away by neighbours. The probability that an individual female returnedand solicited mating from a male was 15 times higher for the male she was chased away from comparedto the neighbour that chased her away. Females returned as often or more to the territory owner afterbeing disrupted, compared to after leaving the territory without being harassed. Our results suggest thatfemale great snipes are extremely choosy, but also that females do not gain direct bene¢ts (harassmentavoidance) by mating with certain males. Females appear to have neither direct nor indirect preferencesfor dominance that could give them such bene¢tsöfemales appeared choosy despite, not because of,harassment. If females gain indirect bene¢ts (genetically superior o¡spring) by being choosy, this is alsolikely to be unrelated to any dominance among males.

Keywords: lek paradox; dominance; harassment; disruption; mate choice; Gallinago media

1. INTRODUCTION

Mating success varies greatly among males in manyanimals having a lek mating system (Bradbury et al. 1985;Wiley 1991; HÎglund & Alatalo 1995; Mackenzie et al.1995). This skew provides strong opportunity for sexualselection. Many lekking species are sexually dimorphicand this has been used as evidence that sexual selection isparticularly strong. Several mechanisms that couldgenerate mating skew on leks have been suggested,including female mate choice, male competition formates, female copying and chance (HÎglund & Alatalo1995; Mackenzie et al. 1995). How much freedom femaleshave to choose males in lekking species is controversial(see Balmford 1991; Wiley 1991; HÎglund & Alatalo 1995;Carbone & Taborsky 1996; Clutton-Brock et al. 1996).Some have argued that female mate choice is free frominterference from male competition for mates (e.g. Brad-bury & Gibson 1983), while others have emphasized thatmale competition and male dominance relationships (e.g.Beehler & Foster 1988) constrain any female choice (atleast within leks) or that females let males decide amongthemselves by inciting ¢ghts. This disagreement may ormay not re£ect variation between species. Separating thee¡ects of female mate choice and male competition onmale mating success might be di¤cult empirically. A

correlation between a male trait and mating success neednot be due to a female preference for the trait, but ratherbecause the trait gives males an advantage in interactionswith other males.

(a) Male competition, and direct and indirect femalemate choice

Teasing apart the e¡ects of female mate choice andmale competition on mating skew may not only be di¤-cult, but in fact impossible. At least two reasons exist forthe dichotomy between mate choice and competitionbeing meaningless. First, females might show direct matechoice based on dominance (but see QvarnstrÎm &Forsgren 1998). Females have been suggested to discrimi-nate between males, e.g. by observing male^male inter-actions (see the references in Trail & Koutnik (1986)).Second, indirect mate choice will set the conditions formale competition (Wiley & Poston 1996). As an example,take the often-claimed (but seldom tested) preference offemales for mating at central positions at a lek or thepreference of female antelopes (Deutsch & Nefdt 1992)for mating at heavily used locations at leks. These femalepreferences will indirectly cause a relationship in malesbetween success in male^male interactions and success inobtaining mates, because males compete over the posi-tions preferred by females. The above arguments alsoapply to sexual selection. Partitioning sexual selectioninto intrasexual and intersexual may be impossibleöthe

Proc. R. Soc. Lond. B (1999) 266, 1227^1234 1227 & 1999 The Royal SocietyReceived 8 February 1999 Accepted 8 March 1999

*Author for correspondence (sas@alfa.itea.ntnu.no).

same trait can be both armament and ornament(Berglund et al. 1996) or female preferences can indirectlycause selection on traits favourable in competitionbetween males (Wiley & Poston 1996).

Nevertheless, it is of interest (i) to learn how freefemales are to choose among the males at leks, (ii)whether females show direct preference for dominantmales, and (iii) whether females show any indirect prefer-ences (e.g. for territory positions or safety from harass-ment) that eventually cause dominance to be related tomating success.

(b) Direct and indirect bene¢ts of choiceIf females show direct or indirect preferences for domi-

nant males, it is conceivable that females might gaindirect bene¢ts from mate choice at leks, e.g. by avoidingharassment from subordinate males. These bene¢ts,although likely to be small, could outweigh the smallcosts of mate choice at leks. These costs are thought to besmall, since comparing many potential mates in a shorttime may be relatively easy at leks. This scenario of `smalldirect bene¢ts^small costs' has been suggested to providea solution to the lek paradox (Reynolds & Gross 1990).Mate choice at leks (or in other systems where femalesreceive no material bene¢ts from males) appears paradox-ical because female preferences will be expected to disap-pear if preferences are for heritable traits. This is becausegenetical variation in male traits preferred by femaleswill be expected to be lost and, hence, the reason formaintaining female preferences (indirect, genetic bene¢ts)will also be lost. The lek paradox has been suggested asresolved by arguing that (i) females are not choosy afterall, matings being instead determined by male inter-actions, (ii) mechanisms exist that maintain variationdespite selection (Pomiankowski & MÖller 1995; Rowe &Houle 1996), (iii) the bene¢ts of choice are not genetic(indirect) but instead a¡ect the female directly (Reynolds& Gross 1990; Kirkpatrick & Ryan 1991), or (iv) prefer-ences vary among females (Brown 1997; Jennions &Petrie 1997;Widemo & S×ther 1999).

(c) Disruptive behaviour, mate choice and the lekparadox

One common aspect of male competition in lekkinganimals is disruptive behaviour, where males intrude andterminate female courtship visits to other males (Foster1983). This is an interesting behaviour since it is `the onedirect means of thwarting female choice that is availableto the males of lek species' (Trail 1985a, p.778) asopposed to causally more indirect, di¤cult-to-observeand vaguely de¢ned behaviour (in a territorial system)such as `dominance'. In some lekking ungulates, femalesmating at leks may su¡er less disruptions and harassmentthan outside leks (Nefdt 1995) and these direct bene¢tsmay explain the evolution of lekking itself in ungulates(Clutton-Brock et al. 1993). If females have direct orindirect preferences for dominant males, we expect malesachieving mating success to be less likely to su¡er disrup-tion and mating success should be negatively related tothe likelihood of su¡ering disruption. If females havedirect preferences for dominant males, individual femaleswill be expected to avoid males they are being disruptedfrom and possibly to prefer disrupters. Likewise, if

females gain direct bene¢ts from mating with particularmales that can protect them from harassment, femalesshould prefer such males and we should expect to ¢nd anegative relationship between male mating success andthe tendency to su¡er disruptions.

The present investigation aimed at understanding thein£uence of male^male competition on female matingbehaviour and male mating success in the lekking greatsnipe (Gallinago media). We show that, though common,disruptive behaviour by neighbouring males does notalter the mate choice of individual females and does notcause males su¡ering disruptions to be less successful. Weargue that this provides clear evidence for the importanceof direct female choice on male mating success andevidence against direct bene¢ts of mate choice in the formof protection from harassment. Hence, direct bene¢ts areunlikely to explain the lek paradox in this species.

2. METHODS

(a) Field methodsThe great snipe is a relatively rare shorebird inhabiting

mountainous marsh areas (in Scandinavia) or £ood marshes (inthe Baltic, Poland and former USSR), being formerly morewidespread in Europe. The study site was in GÔvÔlia (62817'N,98 36'E), Norway (see LÖfaldli et al. 1992). The study populationoccupies several leks where snipes have been caught in mist-netsand individually marked. The data presented here werecollected in 1994 (leks 2, 5 and 12), 1995 (leks 2, 5 and 12) and1996 (leks 2, 5 and 10) from mid-May to mid-June. One to fourobservers (depending on the number of males present) madeobservations at these leks from 23.00 to 02.30, the time whenfemales visit leks (KÔlÔs et al. 1995). Usually, no unoccupiedspace exists between male territories in this species and a maleterritory occupies ca. 100m2 on average (Fiske et al. 1994). Thenumber of males at a lek is usually between ten and 25, butvaries somewhat during the mating season and between leks(S. A. S×ther, P. Fiske and J. A. KÔlÔs, unpublished data). Eachobserver continuously surveyed all visits by females to anassigned subset of the males, noted all copulations and solicita-tions by females and paid particular attention to when and howfemales departed a territory. These courtship visits could beterminated in one of the following ways: (i) the female walkedout of the territory and into another male's territory or out ofthe lek; (ii) the female £ew out of the territory; (iii) the maleterritory owner chased her out of the territory; (iv) anotherfemale chased her away; (v) the female disappeared to theobserver in the Carex/Salix vegetation and the mode of departurewas thus unknown; or (vi) another male chased her out of theterritory. We call cases of this last category disruptions. Thesewere usually caused by immediate neighbours of the territoryowner intruding the territory and approaching the female.Often these attempts were put to a halt by the owner and onlythose attempts that caused the female to leave the territory areconsidered as disruptions here. In addition, it can be noted thatseveral cases were observed when intruders were unsuccessful, inthat a female refused to take o¡ but instead squeezed herselfdown in the vegetation. Usually, the territory owner would soonarrive and chase away an intruder. However, neighbours oftenmanaged to chase away a female even if the male owner wasnearby. A male intrusion was often followed by a ¢ght withinthe territory and, if the female had not already been chased o¡,she often was during such ¢ghts. Disruptions seemed to be

1228 S. A. S×ther and others Pushy males and choosy females in a lekking bird

Proc. R. Soc. Lond. B (1999)

directed at one speci¢c female (or sometimes several) and,consequently, was not simply a side-e¡ect of males intrudingterritories for other reasons. Since females that departed by£ying away and in particular by being chased away wereunlikely to go unnoticed, most cases of females disappearing inthe vegetation probably involved females that eventually walkedout of the territory.

Female great snipe solicit copulation by adopting an easilyrecognized squatting posture. Disruptions of soliciting femaleswere rare (27 out of 1143 solicitations observed in 1994^1998,irrespective of whether the female left the territory whendisrupted and including unidenti¢ed females). Because of thescarcity of such disruptions they were not dealt with furtherunless the disruption caused the female to leave the territory.

(b) MaterialIn this study, we pooled observations from leks and years and

analysed relationships on a bird-year basis, counting each indi-vidual once a year. The study populations in 1994, 1995 and1996 consisted of 86, 82 and 70 marked males, respectively, and47, 44 and 39 marked females, respectively (238 male-years and130 female-years).We made 815 observations of identi¢ed femalevisits to male territories in 1994^1996, involving 92 female-years(68 individual females). These observations lasted on average13.8 min (s.d.�19.3, median� 7, range�1^162, n� 734). For444 out of these 815 observations, we knew how the visit wasterminated and in the rest of the cases the females disappearedin the vegetation.

(c) AnalysesWe analysed the e¡ect of disruptions on males and females in

three basic ways.

(i) First, we analysed whether the probability that malessu¡ered disruption was related to their mating success. Thisprobability was based on the number of female visits to amale terminated by disruption from third-party males,divided by the total number of female visits to the male.Only visits by marked and identi¢ed females were includedin this and all subsequent analyses. Since individual femalesoften mate several times in a mating season (Fiske & KÔlÔs1995) we did not simply sum up the total number of matingsa male received as a measure of mating success. Instead, wetried to estimate the number of individual females thatmated with the male. This was done by combining therecords for identi¢ed females with the minimum number ofdi¡erent unmarked females mating with the male. Thislatter number was calculated by the criteria that anunmarked female could mate on three consecutive nights(Fiske & KÔlÔs 1995). We could sometimes keep track ofseveral unmarked females and, thus, distinguish betweendi¡erent unmarked females mating on the same night, butnot across nights. However, most females were marked. Wecalculated mating success only for males that were observedterritorial on at least ¢ve nights. A successful male is herede¢ned as a male that obtained at least one mating in thespeci¢c season. Some females were only seen to solicit copu-lation and not actually to copulate. These females were alsoincluded in a male's mating success since they had probablymated with that male (Fiske &KÔlÔs1995).

(ii) A more powerful and informative test of the e¡ects ofdisruptions on male mating success is to analyse disruptionson an individual female basis. In other words, we asked

whether the probability that a female is disrupted isdi¡erent when at the territory of the male she chooses tomate with compared with when at the territory of othermales. We analysed this by computing the probability foreach individual female that she su¡ered disruption when atthe territory of the male she preferred compared with whenat the territory of any other male. A preferred male isde¢ned here as the male a speci¢c female mated or solicitedmating with in the speci¢c season. If a female copulatedwith more than one male, only the male with whom shecopulated the most was classi¢ed as her preferred male.Weexcluded females not seen to solicit mating and females notseen with non-preferred males. First, we made analysessimply using the proportion of visits disrupted when witheach of the two groups of males. Second, it could be arguedthat what matters to a female is the likelihood of su¡eringdisruption per time unit spent at a territory and this candi¡er between the two groups of males. Therefore, we alsomade analyses where, for each female, we divided thenumber of disruptions by the total number of minutes shewas observed within the territories of each group of males.This sample was slightly smaller since, for a few females,we did not have observations where the length of the visitswas known for both groups of visited males.

(iii) `Especially informative will be quantitative data on thesuccess of interfering males following disruption . . .' (Foster1983, p. 69). Therefore, we made a third group of analyseswhere the subsequent behaviour of a female following adisruption was focused upon. For each case of disruption wechecked whether the female returned (later in the matingseason) and, if so, if she also solicited mating. This waschecked for the male that disrupted her, for the male shewas disrupted from and for a randomly chosen neighbour.This neighbour was selected from the neighbours of themale su¡ering the disruption (excluding the disrupter) bymeans of a dice, for each disruption separately. The prob-ability that a female returned (or also solicited) to each ofthese male categories was then calculated for each femaleas the average over all disruptions she su¡ered within amating season. This allowed us to compare the probabilitiesof returning (and soliciting) to the male su¡ering disrup-tion versus returning to the other males. We could also testwhether performing disruptions implied bene¢ts such asredirection of mate choice towards the disrupter (bycomparing disrupter versus random neighbour). Finally, foreach female we calculated the probability that she wouldsubsequently visit (or solicit to) the territory owner aftervisits that were not terminated by disruption. This wasdone in order to compare this with the probability ofreturning to the territory owner after disruptions, to seewhether females avoided males from which they weredisrupted.

All statistical tests were non-parametric, although wepreferred to present mean values and their 95% con¢dencelimits in the ¢gures. The p-values are two-tailed.

3. RESULTS

(a) Causes of female departures from territoriesThe overall proportion of female visits terminated by

disruption was between 32.3% (¢gure 1, all observations)and 59.5% (excluding those with unknown mode of

Pushy males and choosy females in a lekking bird S. A. S×ther and others 1229

Proc. R. Soc. Lond. B (1999)

departure). The true percentage was probably closer tothe former ¢gure since disruptions were less likely to gounnoticed by observers when females went out of sightcompared with the other modes of departure such aswalking out of the territory.

(b) Disruptions of female visits to territories ofsuccessful versus unsuccessful males

We observed 795 courtship visits by 68 identi¢edfemales (92 female years) to identi¢ed males which wereassigned as mating successes. Among males that mated atleast once in a given year (n� 28), 233 out of 694 femalevisits (33.6%) were disrupted by other males. For unsuc-cessful males (n� 29) the proportion of disrupted visitswas 26 out of 101. Analysed on a per male-year basis wefound no signi¢cant di¡erence between successful andunsuccessful males in the proportion of female visits thatwere disrupted (¢gure 2a; Mann^Whitney U-testz�71.47, p� 0.14, only counting males that were visitedat least once in a year). If anything, males that mated hada higher not lower probability of having female visitsterminated by disruption (¢gure 2a). Within the group ofmales that mated, we found no signi¢cant relationshipbetween mating success and proportion of visits disrupted(¢gure 2b; Spearman's r� 0.28, n� 28, p� 0.072). Again,if anything, the relationship was positive.

(c) Disruptions of female visits to territories ofpreferred versus non-preferred males

Individual females were more likely to be disruptedfrom the territory of their preferred male than from terri-tories of other males (¢gure 3a; Wilcoxon's matched-pairs, signed-ranks test z�73.38, n� 51, p50.001).

This result indicates that females do not discriminateagainst males whose territories they had been disruptedfrom. Analysed on a per time-unit basis, instead of pervisit, we found no signi¢cant di¡erence in the likelihoodof being disrupted between visits to preferred andnon-preferred males (¢gure 3b; Wilcoxon's matched-pairs, signed-ranks test z�70.75, n� 48, p� 0.47), theobserved di¡erence being in the same direction asbefore.

(d) E¡ects of disruptions on female behaviourA ¢nal approach was to look even more directly at the

e¡ects on individual males of disrupting individualfemales. We computed the probabilities that those indivi-dual females, after a disruption, would return (¢gure 4a)and solicit mating (¢gure 4b) with the disrupting male, anon-disrupting neighbour and the male from which shewas disrupted.

Females did not return (¢gure 4a) or mate (¢gure 4b)with the disrupter more often than with a randomly chosenneighbour. This result strongly indicates that females donot prefer to mate with disrupters and that they do notredirect their mate choice to disrupters. On the contrary,females returned (¢gure 4a) and solicited mating(¢gure 4b) with much higher probability to the male thatthey had been disrupted from, compared to the disruptingmale or the randomly chosen neighbour (Friedman's two-wayANOVA, returns �2�40.2, n� 53, d.f.�2, p50.0001and solicitations �2�34.67, n� 39, d.f.�2, p50.0001).Females were as likely or more likely to return (¢gure 4a),and somewhat more likely to solicit (¢gure 4b; Wilcoxon'smatched-pairs, signed-ranks test z�71.99, n� 35,p� 0.046) with the territory owner after being disrupted

1230 S. A. S×ther and others Pushy males and choosy females in a lekking bird

Proc. R. Soc. Lond. B (1999)

400

350

300

200

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0

50

mode of courtship termination

no. o

f ob

serv

atio

ns

����������unknown

disrupted by neighbourwalks out undisturbedflies out undisturbedchased by territory owner

chased by another female

Figure 1. The frequency of courtship disruption and the otherways in which females depart from male territories. Data arefor identi¢ed females in 1994^1996.

male category

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(a)n = 28

n = 29

male mating success0 5 10 15 20 25

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Figure 2. (a) Probability (mean+ 95% con¢dence limit) offemale visits being terminated by disruption by other malesfor males with and without mating success. The probabilitieswere computed for each male as the proportion of visits thatwere disrupted. (b) Probability of female visits being disruptedby other males in relation to mating success (minimumnumber of di¡erent females mating) for males that obtainedat least one mating.

compared with when they were not disrupted. This lastresult constitutes direct evidence that females do not avoidmales with whom they su¡er disruptions.

4. DISCUSSION

(a) Females are choosy despite being harassed bymales

Disruptions were a common feature at great snipe leks.However, females did not avoid revisiting males theywere chased away from and did not preferentially matewith disrupting males as suggested for another lekkingspecies (Trail 1985b; Trail & Koutnik 1986). On thecontrary, females were much more likely to return andmate with the male they were chased away from ratherthan with the disrupter or with other males. Therefore,we conclude that it is not important in the mate choice ofa female whether she is disrupted or not from a potential

mate. Female great snipe visit the leks for many nightsbefore mating and usually mate with the male on morethan one night (Fiske & KÔlÔs 1995). The females seemedto have decided whom to mate with before actuallymating and were not easily dissuaded by disrupters evenwhen repeatedly disrupted. Thus, females were choosydespite not because of the high levels of harassment. Thisis evidence against direct bene¢ts explaining the lekparadox in this species.

(b) Dominance is not likely to be important in thedistribution of matings within leks

Disruptions may have an impact on female matingpatterns with or without the presence of dominance rela-tionships among males. However, because disruptivebehaviour was so common and did not seem to havemuch impact on female mating patterns, dominance isunlikely to be important in in£uencing male mating

Pushy males and choosy females in a lekking bird S. A. S×ther and others 1231

Proc. R. Soc. Lond. B (1999)

prob

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ing

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r m

inut

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preferred non-preferred

n = 48 females(b)

Figure 3. Probability (mean + 95% con¢dence limit) that afemale is disrupted when at the territory of the male shemated with (her preferred male) compared with when at theterritory of other males. (a) Analysed per visit. For eachfemale these two probabilities were computed as theproportions of her visits to the respective males that weredisrupted, based on 662 observations of courtship visits by 51females (397 visits and 159 disruptions with a female'spreferred male and 265 visits and 53 disruptions with anon-preferred male). Only females observed at least oncewith both their preferred and a non-preferred male areincluded. (b) Analysed per minute the visit lasts. This sampleconsisted of 614 observations of 48 females for a total of8373min.

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n = 74 females

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territory owner disrupter neighbour

(b)

Figure 4. The e¡ect of courtship disruption on subsequentfemale behaviour. (a) The probabilities (mean+ 95%con¢dence limit) that females returned to di¡erent categoriesof males after a courtship disruption. Also shown is theprobability of returning to the territory owner when thefemale visit was not terminated by disruption. DV, disruptedvisits; NDV, non-disrupted visits. The values used are themeans for each female (to avoid pseudoreplication) and onlythose visits where the female was later (on a subsequent,separate visit) observed at least once are included in thecalculation of these probabilities. (b) As in (a) for theprobability of females returning to solicit. Only those caseswhere the female was subsequently seen on at least one visit tosolicit are included here.

success. We do not think dominance is an importantaspect of the behaviour of lekking great snipe males. Wefound no evidence that `dominant' males can control`subordinate's' reproduction, since the tendency to su¡erdisruption was higher for males obtaining mating success.Nor is there any evidence that females prefer centralterritories or speci¢c locations at the lek that males could¢ght over (HÎglund & Robertson 1990; Fiske et al. 1994;S. A. S×ther, P. Fiske and J. A. KÔlÔs, unpublished data).

Neither the presence or absence of dominanceprecludes female choice on the basis of indirect bene¢ts.An absence of dominance does preclude indirect bene¢tsmediated by direct or indirect choice of dominantmales, but not indirect bene¢ts in general. We arguethat the data suggest that there are no dominance rela-tionships between males. Although that may not betrue, if we assume that the tendency to su¡er disruptionis related to dominance, then the results at least indicatethat females do not prefer dominant males and, there-fore, do not obtain indirect bene¢ts in this way. Whetherthey obtain indirect bene¢ts in other ways is still anopen question.

The existence of some sort of dominance hierarchyshould not be taken for granted in any lekking species.We question its existence in the great snipe, although anearlier study (HÎglund & Robertson 1990) claimed to¢nd a linear dominance rank hierarchy using theoutcome of ¢ghts to calculate dominance relationships.However, this is ambiguous because males are terri-torial. Asymmetries in ownership will thereforeconfound relationships between dominance rank basedon ¢ghts and mating success. As acknowledged byHÎglund & Alatalo (1995), this is precisely the case inthis species because `. . . males often visited by femalesremained in their territories while unpopular males lefttheir territories to attack males when the successfulmales had female visits' (p. 69). We think our approachaddressing the e¡ects of disruptions on female behaviourprovides a more direct and reliable way of testingwhether any dominance relationship can be important.In short, the results suggest that (i) females do not havedirect preferences for dominant males, (ii) females donot have indirect preferences for dominant males withinleks, (iii) the distribution of matings within leks is notin£uenced much by male competition for mates, and(iv) females are highly choosy and may possibly havedirect preferences unrelated to dominance, for indirectbene¢ts.

However, this is not to say that male competition formates is unimportant in the distribution of matings inthis species. There is an additional way in whichindirect female mate choice may restrict their set ofpotential mates, although in a more trivial sense. Somemales visit leks without establishing territories and thismay be related to male^male competition (Gratson etal. 1991; HÎglund & Alatalo 1995). In this way indirectfemale choice (Wiley & Poston 1996), because of apreference for mating at leks, may in£uence the distri-bution of matings by setting the conditions for competi-tion.

Nevertheless, among those males that establish a terri-tory and maintain it, there is apparently not much scopefor third-party males to interfere with female mating

decisions, apart from delaying matings. The availableevidence also suggests that female mating decisions arenot based on male competitive behaviour. On thecontrary, we think direct female choice of mates hasseldom been so clearly demonstrated as in this species:despite frequent disruption of females' courtship visits,females returned to their preferred male and mated.

(c) Why do males disrupt?The above arguments prompt the question, what is the

bene¢t for males of performing disruptions? We willbrie£y mention four possibilities. We note from the outsetthe problem that even small bene¢ts, which are di¤cultones to detect, can make the behaviour worthwhile if thecosts are low.

(i) Females may sometimes ¢nd the delay caused bydisruption in mating with the preferred male toocostly. Hence, male interference might constrainfemale choice by introducing time costs. However,this seems unlikely to be very important, sincefemales spend several days at the lek and usuallymate more than once, although choosiness may belower late in the season or vary among females.Disruptions seem to have a rather low in£uence onthis potential trade-o¡ between the costs of delayingbreeding and mating with the preferred male, sincefemales show a remarkable resoluteness to returnafter being disrupted. The potential bene¢t to disrup-ters of a small number of females mating withanother male than her preferred may very well haveto be shared with other non-disrupting males. Yet, itmay pay o¡ as long as females do not actively avoidprevious disrupters. This may indeed be the casesince there were no signi¢cant di¡erences betweenthe disrupter and the randomly chosen neighbour.Disrupters seem to be neither discriminated againstnor favoured by females, simply ignored in mostcases.We point out that the small numbers of femalessoliciting matings from their disrupters or neighbours(¢gure 4b) should not be interpreted as femaleshaving redirected their choice to these males. Inthese cases it could simply be that the female wasbeing disrupted when at the territory of a non-preferred male.

(ii) Another occasional bene¢t may occur for males ifdisruptions are actually attempts at forced copula-tions. Only limited anecdotal evidence exists on thepossibility of males mating with non-solicitingfemales in this species: one female disrupted by aneighbour was pursued and got stuck in the vegeta-tion, but managed to free herself as the male wasseemingly about to attempt copulation. Males oftenpursue disrupted females out of the lek area for sometime before returning to their territories. Althoughseeing what happens outside the lek can be di¤cult,we have no indications that females solicit matingsoutside lek territories.

(iii) A related possibility is that disruptions may beattempts at copulation with females soliciting to theterritory owner. Interruption of solicitations is infre-quent (see ½ 2(a)) but we have four observations ofmales managing to mate with females inside other

1232 S. A. S×ther and others Pushy males and choosy females in a lekking bird

Proc. R. Soc. Lond. B (1999)

males' territories. In two of these cases the disruptingmale physically displaced the territory owner fromthe back of the female and copulated with the stillsoliciting female. However, since most disruptionsinvolved females not soliciting mating, this seemsinadequate as an explanation.

(iv) A ¢nal possibility (which was suggested by a referee)is that the bene¢t lies not in mating with the femaledisruptee but, rather, in removing any opportunity tocopy among females, who may otherwise be attractedto males with many females present. However, thisseems unlikely since females may also be attracted bythe increased activity caused by disruptions. Based onthe distribution of matings in time, Fiske et al. (1996)argued that copying is unlikely to be important ingreat snipe mate choice.

Some questions remain. Why are visits to moresuccessful males more likely to become disrupted? Whyare females more likely to be disrupted when with theirpreferred male? Why are females more likely to solicitmating from the male after being disrupted than whennot being disrupted? The answer to all these questionsmight be that, for some reason, the disrupting males aremore interested in disrupting fertile females. If fertilefemales have ¢nished mate sampling, they will bespending most of their time (when at the lek) with theirpreferred male. This will create a bias in the likelihood offemales being disrupted with respect to both overall malemating success and status as preferred by the individualfemale. We suggest the reason why males are more inter-ested in disrupting fertile females is that these females aremore sensitive to time costs, as explained above.

(d) ConclusionsScenarios where females obtain good genes from high-

quality males by preferring dominant males directly donot seem to apply to the great snipe. Other studies haveshown that such indirect bene¢ts do not come fromindirect preferences of dominance either (such as centralpositions or speci¢c locations within leks; Ho« glund &Robertson 1990; Fiske et al. 1994; S. A. S×ther, P. Fiskeand J. A. KÔlÔs, unpublished data). It thus appears to bea con£ict between female preferences and male competi-tion for mates, in contrast to the more harmonious viewthat females might somehow use male competition toselect genetically high-quality males (see also QvarnstrÎm& Forsgren 1998).However, the results presented also strengthen the

possibility that female great snipes choose mates forgenetic (indirect) bene¢ts for their o¡spring rather thandirect bene¢ts. Our results suggest that the lek paradox isnot solved by direct bene¢ts of harassment avoidance inthis species.

Thanks are due to F.Widemo, P. T. Smiseth and the referees forcomments and to those who helped us in the ¢eld in 1994^1996,in particular T. Bretten, J. M. Gjul, S. KÔlÔs, P. T. RintamÌkiand S. L. Svartaas.

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