Spatial and temporal dynamics at manakin leks: reconciling lek traditionality with male turnover

Leks, display grounds where males congregate and females visit to copulate, are typically traditional in location, despite often high turnover of individual males. How leks can persist in face of male turnover is not well understood, in part due to a lack of detailed field data allowing for a clear understanding of lek dynamics. We followed the fate of individual males at 11 to 15 leks of the blue-crowned manakin Lepidothrix coronata across four breeding seasons to gain insights on how leks are formed and changed in space and time. Between years, leks were traditional in location despite changes in territory ownership due to male disappearance and recruitment. New males were equally likely to recruit by taking over existing territories or by establishing new territories. Recruitment was influenced by age, as recruits were more likely to be adults than subadults. Lek size did not affect the probabilities of a male recruiting or persisting at a territory, and vocalization rate, a correlate of mating success in this population, did not affect male persistence. We used our field data to model changes in lek size and composition over longer periods of time (100 years) to understand how lek traditionality can be reconciled with high male turnover. Our simulations showed that leks in our population rapidly stabilize in size despite changes in territory ownership and that rates of male recruitment and disappearance compensate each other, such that leks have the potential to persist for several decades after the original males have disappeared from them.     

Uganda kob mating success does not increase on larger leks

One explanation for the movement of sexually receptive females to clusters of male territories in lek-breeding species is that larger clusters provide females with higher-quality mating partners, as would be the case if males were distributed between leks in an ideal free distribution for unequal competitors. This ideal free model of lek evolution predicts that male competitive ability and mating success will be greater on larger leks than smaller ones. I tested these predictions by comparing the mean number of males on 19 different Uganda kob leks with the sex ratio, the availability of oestrous females, mating rates, male fighting rates and male turnover rates. Contrary to the predictions of the model, numbers of females, receptive females and fights increased proportionally with lek size, but were no greater per male on larger leks. Multivariate analyses of male and female numbers on leks showed that male numbers were associated with female numbers, female numbers in the past, and a variety of habitat variables which may have related to the costs of holding a lek territory, but female numbers varied only with male numbers and female density in the area. These data do not provide evidence that females gain access to superior males by mating on larger leks, though they do support the possibility that lekking may be promoted by a tendency for larger leks to retain females longer.     

Costs and consequences of variation in the size of ruff leks

Summary We studied 13 ruff leks in a small region on the island of Gotland (Sweden) to investigate the effect of lek size on the costs and benefits of lekking for individual males. Male ruffs occur in two behaviourally and morphologically distinct forms, independents (residents plus marginals) and satellites, whose costs and benefits we have assessed separately. These ruff leks had from 1–10 resident (territory-holding) males and were visited daily by satellites, marginals and females from 5–25 May, when most copulations occurred. We used the average number of independent males, counted during censuses taken every 5 min during 2-h observation periods at each lek, as an index of mean lek size. Per independent male, the numbers of both satellites and females increased significantly with mean lek size. Female arrival rate and attendance (total female-minutes) also increased significantly with mean lek size as did the average per capita rate of mating success for resident males (that of satellites was not quite significant). Thus, the dispersion of both of these male categories did not appear to fit an ideal free distribution with respect to mating success. In addition, the number of independent-independent fights per independent and the rate of satellite-resident dyad formation per resident increased significantly with mean lek size. These results suggest that ruffs on larger leks enjoy higher mating success than those on smaller leks but also that costs increase with lek size. We suggest that independent males distribute themselves so as to maximize their own net benefits and that this factor can account for both the occurrence of ruff leks and the variation in their size. Correspondence to: J. Höglund     

Female defence polygyny in the bumblebee wolf,Philanthus bicinctus (Hymenoptera: Sphecidae)

Summary In the digger wasp Philanthus bicinctus the first adult males emerge about a week before the first females. The sex ratio of emerging wasps is near unity. Females appear to mate once and do so when they first start to nest, not when they first emerge.Males defend mating territories in a large area of female ground nests. Territoriality begins when females first start to nest and throughout the season coincides with the digging activities of females initiating rests. During the day territoriality occurs only when females are engaged in digging activities.Males compete for certain territory sites within the resting area; the most frequently occupied male territories are in areas where the density of nests is highest. About half of the males are excluded from nesting area territories. Some of these males defend areas among the flowers of snakeweed where females occasionally forage; this appears to be a loser tactic of males unable to obtain nesting area territories.Although there was no significant difference in the sizes of males on nesting area and snakeweed territories, within the nesting area larger males usually occupy territories with the higher nest densities.     

The significance of hotspots to lekking topi antelopes (<Emphasis Type="Italic">Damaliscus lunatus</Emphasis>)

Controversy has surrounded the question of why lek-breeding has evolved in certain ungulate species. Can the behavior be explained simply by males mapping onto a female distribution that is determined by factors unrelated to mating? Or are leks created because estrous females distinguish between males and favor males who cluster? Here I address these questions by looking at spatial distribution in lekking topi antelopes (Damaliscus lunatus). Contrary to the predictions of a model assuming male clustering in the zone of maximum female range overlap, territories were highly clustered also within this zone, and lek size correlated positively with population density. In support of models derived from the ideal free distribution of males onto female dispersion, leks were in areas with high female density during the rut. However, models not taking into account both individual variation in male quality and female mate preferences failed to explain the extreme male clumping also within high density areas, which was revealed by a strongly male-biased sex-ratio on leks. Additional support for the female preference-based model came from the finding that estrous females concentrated onto leks. Female preference for clustered males may develop if males initially follow an ideal free distribution of unequal competitors with high quality males slightly clustered at density hotspots; positive feedback between female benefits of preference for clustered males and male benefits of clustering could lead to contraction of the territorial network and lek behavior. Thus only the female preference-based model correctly predicted a negative correlation between male mating rate and resource density.     

Conditional lekking in ruff (Philomachus pugnax)

Summary In our study of ruff, a lekking shorebird, we found that the lek ratio — the proportion of the total population of males occurring on leks was low, averaging 12% over the breeding season (Fig. 1D). Off-lek males spent approximately the same proportion of time as lek males in displaying to females (Fig. 4). We defined three spacing tacties that male ruffs use to position themselves to court females: Following — directly pursuing females, and two types of lekking behavior, Intercepting — waiting for females at resource-rich sites, and True Lekking — waiting for females at places without any resources other than the males themselves. Males switched among these tactics, causing the lek ratio to vary over the season (Fig. 1 D). Lek ratio increased when the number of females present in the study area plummeted at the end of May, and was positively correlated throughout the season with the copulation rate of the preceding day, suggesting that males were tracking the behavior, as well as the number, of females available (Table 1, Fig. 1). Early in the season, males off leks spent most of their time feeding (Fig. 4), and lek ratio was positively correlated with temperature (Table 1), suggesting that some males may have been unable to lek during cold weather. Males on leks mated at significantly higher rates than Followers (Table 4). On average, males at our interception lek were less site faithful and less peristent than males at true leks, and the interception lek itself disappeared after females stopped coming to use its adjacent resource (Table 2, Fig. 5). The most successful individuals in our population were the True Lekking males, rather than the Interceptors.In addition to the conditinal lekking tactics described here, ruff display a dimorphism in behaviorat leks. Independent males defend small courts on leks, while Satellite males share courts and mutually display with independents Both independents and satellites may use all three conditional tactics. We propose that satellites evolved as specialized. Followers, adept at tracking the movements of females among leks.     

Correlates of male mating success in the ruff Philomachus pugnax,a lekking shorebird

Summary Male ruffs (Philomachus pugnax), a lekking shorebird, can generally be divided into two morphs according to behavior and plumage coloration. Predominantly dark-colored, independent male ruffs defend small territories on a lek, whereas lighter colored satellite males are non-territorial and less site-faithful to a particular lek. The traits associated with the mating success of independent male ruffs were studied at two leks during two seasons on the island of Öland, Sweden in May and June of 1985 and 1987. Using multivariate analyses, three characteristics were found to be significantly related to mating success: high frequency of visits by satellites to an independent male's residence, consistency of lek attendance, and low rates of aggressive behavior. In contrast, mating success was unrelated to the degree of darkness of the independent male nuptial plumage, territory location on the lek, or rate of courtship displays. The use of multivariate analyses helped to resolve conflicting conclusions from previous studies which employed simple statistical analyses, or none at all. Experimental manipulations are suggested which will help to further determine the influence of female mate choice in this lekking system.     

Density dependence and habitat quality modulate the intensity of display territory defence in an exploded lekking species

We evaluated the effect of conspecific abundance and habitat quality of leks on the territorial behaviour of males in an exploded lekking species, the Little Bustard (Tetrax tetrax). The hypothesis that males more intensely defend territories with higher conspecific abundance and better habitat quality was evaluated experimentally analysing the agonistic response of experimental males to male decoys placed on their displaying areas. Decoy experiments showed that the intensity of display territory defence by little bustard males is density dependent. The time experimental males took to return to their display sites after decoy placement decreased with abundance of both males and females. The strength of their final response was positively associated to local male and female abundance in the vicinity of their display sites. Habitat quality also influenced males’ display territory defence since the intensity of male response increased with the degree of natural vegetation cover. Habitat quality was particularly relevant in explaining variation of experimental males’ snort call rate, which decreased with the degree in plough cover and increased with the number of fields in the lekking area. Snort call rate decreased with the level of male aggregation and was lowest in males exhibiting the strongest aggressive response to decoys. These results add new evidence for the density dependence of species’ breeding territorial behaviour, supporting density-dependent models of lek formation and reinforcing the role of resources defence in exploded lek mating systems.     

Correlates of copulatory success in a fallow deer lek

Summary We studied the behavior and copulatory success of fallow deer (Cervus dama) males at a lek. We recorded 471 copulations in 3 years. Most males did not copulate. The top three males accounted for between 60 and 90% of copulations each year. Lek attendance time was the major determinant of male copulatory success, but territory location also affected the number of copulations achieved. Copulatory success was correlated with the number of females in a male's territory and possibly with dominance status, but not with fighting success or fighting rate. All males that defended lek territories were 5 years of age or older. Copulatory success may improve with age. Body condition appears to be an important determinant of male copulatory success, because only males in superior condition could defend a lek territory for up to 2 weeks. Males do not feed while defending lek territories. Foraging ability during the year probably determines condition at the onset of the rut. Females appear to choose mates at least partially on the basis of location, preferring males located near traditional routes. Females may ultimately select mates in the best body condition.     

Extra-pair copulations in a lek: the secondary mating system of monogamous razorbills

Summary I studied the mating strategies of razorbills Alca torda, a monogamous colonial seabird, during 1987–1989 in Wales, U.K. The outstanding feature of the study population's mating system was the performance of most copulations in mating arenas outside the colony. Females visited the arenas and sometimes accepted extra-pair copulations (EPCs), and males aggressively competed for EPCs. During the fertilizable period of most females, the arenas resembled leks because they contained no resources except mates, and males contributed only sperm to extra-pair females. Typical of leks, the operational sex ratio was strongly male-biased, and male mating success was highly skewed. To examine the potential for sexual selection to operate in this system, I correlated male EPC success with variables that could be associated with male-male competition and/or female choice. The frequencies of three behaviors (interference of copulation attempts, fights won against other males, and EPC attempts), accounted for 62% of the variance in EPC success and were strongly intercorrelated, with interference explaining most of the variance in a multivariate test. EPC success was not correlated with body size, age, paired status or either of two estimates of the time spent in the arena. The hypothesis that male EPC success was determined by active female choice was tested by examining the relative success (EPCs per attempt) of males. Relative success was not correlated with any of the three behaviors associated with absolute success, or with age, body size or attendance, suggesting that male-male competition, mainly in the form of copulation interference, is the principal correlate of EPC success. These findings in a monogamous species illustrate that EPC is a secondary mating system of razorbills in which sexual selection operates. The existence of this system outside the colony raises the possibility that lekking for EPCs may also occur within the nesting territories of other monogamous, colonial species but is hidden by competition for nests and breeding partners.     

Females prefer larger leks: field experiments with ruffs (Philomachus pugnax)

Summary Preference by females for choosing mates at male aggregations has been hypothesized as the primary selective pressure favoring the formation of leks, but alternative hypotheses account for lek formation without invoking female preference. Observational studies to determine whether male mating success increases with lek size, as predicted under the female preference hypothesis, have produced inconsistent results, possibly due to covariation of lek size with other variables or to male-male or intersexual conflict over lek size. We tested whether females prefer larger leks in a field experiment with ruffs (Philomachus pugnax), a lekking sandpiper, in which male group size, composition, and location were controlled. Wild females chose the larger of two adjacent groups often enough such that males in larger groups had significantly higher per capita rates of female visitation (Table 3). Such behavior would probably lead to higher per male mating rates at larger leks, which is generally considered a necessary condition for female choice to select for lek display (Fig. 2). Lek size in nature will reflect both female preference for larger leks and competition among males, which may favor smaller lek size. All else being equal, however, female ruffs preferred to visit larger groups strongly enough to maintain lekking by males.     

Sexual selection and cues for female choice in leks of Jackson's widowbird Euplectes jacksoni

Summary Sexual selection through female mate choice was investigated in the lekking Jackson's widowbird by applying multivariate selection analysis to observational data from four leks. Males perform a stereotyped jump display on small display courts (dance rings) constructed by the males in open grassland. Females visit the lek solely for mating and nest on their own, away from the lek area. Few cases of interference during courtship and absence of position effects on mating success indicated that female choice within the leks was not pre-empted by male-male competition. In a set of 11 male traits with mating success as the dependent fitness measure, significant selection differentials (covariances) were found for the length of the conspicuous tail and the rate of the jump display, suggesting sexual selection of these traits. They also showed the largest selection gradients (partial effects) and thereby seem to be the cues on which females base their choice. The success of males in obtaining copulations appears to depend on two components: display rate and lek attendance affect the number of female visits, whereas tail length seems to primarily influence the chance of copulating with a visiting female. Tail length was positively related to a measure of body condition, which is of interest with regard to the suggestions that sexual ornaments may serve as indicators of male viability.     

The evolution of leks through female choice: differential clustering and space utilization in six sympatric manakins

Summary The degree to which lekking and non-lekking male manakins select display sites in order to maximise proximity to females was examined by contrasting movements of females with male dispersion. Data on female visiting patterns, male courtship disruption, and mating skew were also collected over three successive breeding seasons. For the five lek-breeding species, female home-ranges were 3–7 times larger than those of adult males. Female movements were concentrated around leks, fruiting places and stream bathing sites. None of the females monitored by radio-tracking expanded her normal range in order to visit males on leks. On the contrary, feeding bouts of females frequently preceded a visit to potential mates at neighboring leks. Despite small sample sizes, significant correlations were found between female home-range size and male clustering (distances between neighboring leks and distances between neighboring males), as predicted by the female choice model and the hotspot model. Adult and immature male home-range sizes were not significantly correlated with male dispersion or female ranges. On the other hand, males and females of the only non-lekking species exhibited similar use of space and home-range size. Male settlement at sites with high levels of female traffic showed that the hotspot model is adequate to explain differences in male dispersion among sympatric lekking species. Comparisons with other studies suggest that apparent female choice could be overidden by past and present male-male interactions or female mate-comparison tactics. In fact, both the hotspot model and the attractiveness hypothesis appear to shape male dispersion on leks: males appear to settle under hotspot conditions with despotic rules generated through bias in female choice or male-male interference. It is proposed that the evolution of leks is ecologically motivated by the spatio-temporal distribution of trophic resources, initially leading to a dispersed male-advertisement polygyny. Following this, a foraging ecology that promotes high mobility by females and the magnetic effect of mating skew in particular males may have favored clustering on exploded leks. Later, the development of male-male interference and the increasing female home-range size could have led to the evolution of classical leks.     

Bat predation and the evolution of leks in acoustic moths

Theories of lek evolution generally invoke enhanced mating success experienced by males signalling in aggregations. Reduced predation has also been acknowledged as a potential factor driving lek formation, but its role is more ambiguous. Although lekking is a complex behaviour, few empirical studies have investigated the role of both claims. We studied the potential pressures imposed by mating success and predation in an acoustic moth, Achroia grisella, in which males gather in leks and broadcast a calling song attractive to females. We exploited the ability to manipulate the distribution of singing males in laboratory arenas to create different-sized leks and tested female preferences for these aggregations. Because A. grisella are vulnerable to predation by bats while in flight and on the substrate, we also tested the responses of a potential predator, Rhinolophus ferrumequinum, a bat species that feeds on moths, to the experimental leks. We found that the per capita attractiveness of A. grisella males to females rose with increasing lek size. R. ferrumequinum also oriented toward experimental A. grisella leks, but this attraction did not increase at larger leks. Thus, a male’s per capita exposure to predation risk declined as more moths joined the lek. A. grisella males appear to benefit from advertising in larger leks in terms of both increased mate attraction and reduced predation risk. Our results support the idea that multiple factors operating simultaneously may maintain lekking behaviour.     

Imperfect female choice and male mating skew on leks of different sizes

We present a model of error-prone female choice on leks, and investigate the effects of different degrees of error on the distribution of mating success among males present at leks of different sizes. At higher levels of error, the best male is predicted to gain a smaller share of matings, while low-ranking males gain a larger share. Males who are of high rank but not the most desirable on the lek do best at intermediate levels of error, since the top-ranked male does not then claim all the matings, but assessment is still sufficiently accurate for females to discriminate between high-ranking and low-ranking competitors. The effects of error are shown to be more pronounced on larger leks, due to smaller expected differences in mating value between males of adjacent ranks. This interaction between lek size and error suggests that observed negative relationships between lek size and mating skew need not be attributed solely to intrasexual competition, as previously suggested, but could also be a result of imperfect choice. Received: 20 February 1998 / Accepted after revision: 25 October 1998     

Mate choice in the yellow-shouldered widowbird: correlates of male attractiveness

Recent investigations of male ornaments in sexual selection have used experimental manipulation of tail length in three widowbird species, but only for one of these have correlates of male reproductive success been reported. I examined correlates of male attractiveness to nesting females over two breeding seasons for the polygynous yellow-shouldered widowbird, Euplectes macrourus, in order to discover which cues females may be using to select mates. The black, long-tailed ( 10 cm) males defend large territories and build nest frames, or cock's nests, which females then line and use for nesting. I examined various aspects of male morphology, five behavioral displays, territory characteristics, and the number of cock's nests that males built. Few correlates of mating success were found. The best predictor was the number of cock's nests that a male builds, though one courtship display also correlated with male mating success in 1 year, as did average grass height. Tail length did not correlate with male mating success. A partial correlation analysis confirmed that cock's nests and, in 1 year, grass height, were the primary contributers to male success. Females may choose where to nest primarily on the availability of suitable nesting sites. Long tails may be used by females seeking extra-pair copulations or in male-male competition for territories.     

Mate sampling behaviour of black grouse females (Tetrao tetrix)

We studied female mate sampling behaviour in lekking black grouse (Tetrao tetrix). Females mainly visited males occupying territories in the centre of the lek with relatively large territories. They were also more likely to visit males that had high attendance. The same factors were also correlated with male mating success. A multiple regression model including these factors explained more of the variance in female visits per male (53%) than in mating success (33%). The pattern of female sampling conformed with a pool comparison (best-of-n) tactic. Such a tactic is expected if the costs of sampling are low. Females of high body mass visited more males than lighter females, however, which indicates that females may vary in their search tactics and suggests that there may be search costs. The existence of costs is further suggested by the fact that if the mate from a previous year was still present, females always mated with the same male in the following year. Though search costs were not measured directly, our findings suggest that some costs are negligible (e.g. energetic exhaustion or predation) whereas others (timing of mating) may be more important.     

Dispersion of displaying male sage grouse

Summary The degree to which male sage grouse select lek sites and females select nesting sites to maximize proximity to the other sex was examined by contrasting male dispersions with the dispersions and movements of females in the months preceeding incubation. Wintering females exhibit highly overlapping ranges due to shared use of central refuging areas. In late winter and early spring, females move an average 9 km from wintering areas to select nest sites and males begin occupying leks. Pooled evidence suggests that females select nest sites independently of male dispersion whereas males adjust lek occupation so as to maximize proximity to females. Relevant observations include females visiting nest sites before leks, moving further to select a nest site than to select a lek, and increasing their distance to leks as a result of selecting nest sites. In addition, males avoid leks until females have moved to within 5 km of the arenas, abandon early season leks as local female densities drop, and exhibit dispersions in which mean ratios of females/male are similar across leks. Contrasts between predicted and observed dispersions of males showed that hotspot settlement models are adequate to explain male dispersions on very coarse scales (2 km or greater); on finer scales, habitat preferences of males and tendencies for males to cluster tightly must be invoked in addition to hotspots to explain specific lek sitings.     

Neighbours, strangers and male-male aggression as a determinant of lek size

Interactions between males on leks may play an influential role in lek formation and the regulation of lek size. In this paper I present the results of a playback experiment that simulated de novo settlement at sites adjacent to currently existing display territories of the ochre-bellied flycatcher, Mionectes oleagineus. In the study population, males displayed both solitarily and at small leks. A large proportion of males held no display territory at all. A stranger's song was played to both solitary and lekking males from 10 m outside their territorial boundaries. In separate playbacks, lekking males were also played neighbour's song. Both lekking and solitary territorial males reacted to the playback by decreasing their song rate, approaching the playback speaker and, on occasion, attacking the model. Solitarily displaying males responded more aggressively to playback of stranger's song than did lek males. Lek males were able to distinguish between their neighbour's and a stranger's song and did so irrespective of whether it was played from the neighbour's territory or from outside the lek. In addition to distinguishing between neighbours and strangers, lek males modified their responses to these different playbacks depending on where the playback originated. These results suggest that male-male interactions can be influential in structuring leks. In M. oleagineus, interactions between males are aggressive and act to limit rather than augment lek size. Received: 6 March 1996 / Accepted after revision: 9 December 1996     

Spacing of leks in relation to female home ranges,habitat requirements and male attractiveness in the great snipe (Gallinago media)

Summary In an attempt to examine three main hypotheses on the evolution of leks, data on female home ranges, distance between leks and male site fidelity in the great snipe (Gallinago media) were obtained. In a 30 × 40 km area in central Sweden, the locations of 12 leks were identified. Six were within the study area (7 × 11 km) in which probably all leks were known. In the study area, nearest neighbor distances between leks were longer than the predicted drawing area (diameter of female home ranges plus the detection range of leks). Furthermore, in only 1 of 13 radio-tracked females did the estimated home range enclose many leks. These data do not fit the prediction from the hotspot hypothesis on the dispersion of leks, namely, that the distance between leks should be less than the drawing area and hence an average female home range should enclose more than one lek. The observed distance between leks was about the same as predicted by the female preference hypothesis. This hypothesis also predicts females visit mainly one lek; however, we found they sometimes visit two and nest close to a third. We propose that males may first settle according to hotspot rules, but females will resettle according to preferences for certain males and/or larger leks. In this way some hotspot leks are abandoned, and the distance between leks is increased as males become more tightly clumped. However, when all males and females have settled, the leks still existing would be on hotspots. In the female preference hypothesis, males are assumed to aggregate on leks because females prefer clustered males as they can be more easily compared than if they are dispersed. Alternatively, in the attractiveness hypothesis, it is suggested that females prefer certain males, and hence unattractive males surround the attractive are forced to join leks in order to come close to females. Our data on male site fidelity support the attractiveness hypothesis because successful and dominant males return to the same lek and territory, both within and between years, whereas unsuccessful males move to other leks. Attractiveness of certain males may explain why according to hotspot rules in this species males are more clumped than expected. Offprint requests to: J. Höglund