Lek Mating System Research Articles

Skewed paternity distribution in the extremely size dimorphic Musk Duck (Biziura lobata)

Although most species of Anseriformes form long-term or seasonal pair-bonds and breed monogamously, some are thought to be polygynous. The Musk Duck (Biziura lobata) is unique among Anseriformes in that it has been suggested to have a lek mating system. Musk Ducks also display extreme size dimorphism and many secondary sexual traits whose functions are not clearly understood. We studied paternity in a resident population of Musk Ducks in order to explore the genetic mating system and to investigate the role of different male secondary sexual traits. We obtained blood samples from seven males, five breeding females and seven ducklings from six broods on Lake Wendouree, Ballarat, Australia, during the 2003 breeding season and used microsatellite markers to assign paternity to ducklings. Two of the seven sampled males fathered all of the ducklings in the five broods for which we could assign paternity. Both of these males were territorial and heavier, had larger lobes and displayed more frequently than the remaining males. They also produced a large amount of musk. Our results provide the first unequivocal genetic demonstration of polygyny occurring in a wild anseriform population. Discovery of polygyny in Musk Ducks corresponds well with previous field studies suggesting that they have a lek mating system. The skewed paternity distribution towards more ornamented and larger males also suggests that these traits may have evolved under sexual selection.

Predicting fate from early connectivity in a social network

In the long-tailed manakin (Chiroxiphia linearis), a long-lived tropical bird, early connectivity within a social network predicts male success an average of 4.8 years later. Long-tailed manakins have an unusual lek mating system in which pairs of unrelated males, at the top of complex overlapping teams of as many as 15 males, cooperate for obligate dual-male song and dance courtship displays. For as long as 8 years before forming stable "alpha-beta" partnerships, males interact with many other males in complex, temporally dynamic social networks. "Information centrality" is a network connectivity metric that accounts for indirect as well as shortest (geodesic) paths among interactors. The odds that males would rise socially rose by a factor of five for each one-unit increase in their early information centrality. Connectivity of males destined to rise did not change over time but increased in males that failed to rise socially. The results suggest that network connectivity is important for young males (ages 1-6) but less so for older males of high status (ages 10-15) and that it is difficult to explain present success without reference to social history.

LEKKING BEHAVIOR OF ANASTREPHA FRATERCULUS (DIPTERA: TEPHRITIDAE)

Anastrepha fraterculus (Wiedemann) (Diptera: Tephritidae) displays a lek mating system. Males form groups in which they simultaneously display signals (acoustical, visual, or chemical) to attract females with the purpose of mating. Females visit the lek and choose among signaling and courting males to mate. Scarce information is available in A. fraterculus about the main factors involved in female choice and the behavior of displaying males. This information could be important within the context of pest control programs with a sterile insect technique (SIT) component, because departures from normal sexual behavior caused by artificial rearing could affect males’ performance in the field. In this study we assessed A. fraterculus male behavior within the leks and analyzed the importance of behavioral and morphological traits on their copulatory success. The existence of preferred places for lek formation was evaluated in field cages with trees inside and analyzed by dividing the trees in sectors according to a 3-dimensional system. Males were individually weighed, marked, and observed every 15 min. Morphometric and behavioral characteristics of successful and unsuccessful males were compared. Most successful males grouped in a region of the tree characterized by the highest light intensity in the first 2 h of the morning. Results showed that pheromone calling activity is positively associated with copulatory success. Copulations were more frequent for males calling inside the lek, indicating that pheromone calling activity and presence in the lek are key factors for copulatory success. A positive association between copulatory success and eye length was found; some characteristics of the face were also associated with copula duration and latency.

Kin selection does not explain male aggregation at leks of 4 manakin species

In lek-mating systems, males aggregate at display arenas and females visit solely for the purpose of mating. This breeding system is characterized by high variance in male mating success with one male often receiving most copulations. High reproductive skew among males has led to question why males join leks when their chances of reproductive success are so low. Kin selection has been invoked as a mechanism to explain the evolution of lekking behavior, whereby nonreproducing but genetically related males gain indirect inclusive-fitness benefits. Evidence for kin selection among lek-mating birds is, however, mixed. Here, we show that kin selection is unlikely to be an important explanation for evolution of lekking behavior in manakins (Aves: Pipridae). We found that for 4 species chosen from several major clades within Pipridae, males within leks were not significantly more related than expected from random assortment of males in the population. This means that nonreproducing males do not gain indirect inclusive-fitness benefits by joining leks. This result suggests alternative mechanisms must be invoked to explain the evolution of lek-mating systems in manakins.

Individual Male Calling Pattern and Male Mating Success in the European Treefrog (Hyla arborea): Is there Evidence for Directional or Stabilizing Selection on Male Calling Behaviour?

AbstractIn anurans, call properties are commonly classified based on within‐male variability as being either static or dynamic. Numerous playback experiments in the laboratory have indicated that female preferences based on dynamic call properties are usually strongly directional, while female preferences based on static call properties are often stabilizing or weakly directional. However, there are only few studies demonstrating that female preferences for high values of dynamic call properties indeed exert directional selection on male calling behaviour in natural populations. Moreover, field studies investigating whether female preferences for values of static call properties around the mean of the population lead to currently operating stabilizing selection on male calling patterns in natural populations are completely lacking. Here I investigate for two consecutive breeding seasons male calling patterns and male mating success in a population of individually marked European treefrogs (Hyla arborea), a hylid frog with prolonged breeding season and a lek mating system. Individual male calling pattern as analysed in terms of seven temporal and spectral call properties did not differ between males that survived from one breeding season to the next and those not surviving. None of the seven call properties investigated differed significantly between mated and unmated males, indicating that there is no strong directional selection on male calling behaviour in the study population. However, in one study season males that produced calls with a number of pulses around the mean of the population were significantly more likely to obtain matings than males that produced calls with a number of pulses at the low or high end of the distribution. Thus, this study provides preliminary evidence for the operation of stabilizing selection on a static call property (i.e. the number of pulses per call) in a natural population of an anuran amphibian.

Reproductive biology of Scinax fuscomarginatus (Anura, Hylidae) in south‐eastern Brazil

The present study describes the reproductive biology of Scinax fuscomarginatus in a remnant of Cerrado in south‐eastern Brazil. Observations were made between September 2002 and March 2004 at Estação Ecológica de Itirapina, State of São Paulo, south‐eastern Brazil. Breeding activities occurred in lentic and temporary bodies of water during the rainy season. Scinax fuscomarginatus exhibited a prolonged breeding pattern and a lek mating system. Males were smaller than females and defended individual calling areas through acoustic and physical interactions. Resident males consistently won encounters, but did not differ in size or mass from intruder males. Satellite behaviour was observed, but no female or amplected pair interception was registered. Scinax fuscomarginatus exhibited low operational sex ratios and the general reproductive mode in which eggs are laid in the water and tadpoles are aquatic. Amplexus was axillary and the eggs were deposited at the bottom of temporary ponds. Details on oocytes, egg masses, and eggs are included.

Sexual selection in the lek-breeding European treefrog: body size, chorus attendance, random mating and good genes

Variation in male reproductive performance and success was studied over 2 years in a population of individually marked European treefrogs, Hyla arborea , a hylid frog with prolonged breeding season and a lek mating system. Reproductive success in males was not related to body size, age or growth rate, and there was no evidence for size- or age-assortative mating. Male mating success was significantly correlated with chorus attendance, that is, the number of nights spent calling at the breeding site. There were no significant differences with regard to body size, age or growth rate between males surviving to the next breeding season and those not surviving. However, surviving males showed a significantly higher chorus attendance than nonsurviving males, which is a novel finding for lekking anurans. Furthermore, males that survived from the previous breeding season spent significantly more nights calling at the breeding site than males that were observed for the first time. Since calling in frogs is costly, these results suggest that chorus attendance reflects male quality. The distribution of male mating success did not differ from a Poisson distribution, indicating a random mating pattern. Since male quality is related to chorus attendance, females that mate randomly are likely to mate with high-quality males and thereby gain indirect genetic benefits without incurring costs of extended mate searching and mate assessment. We suggest that a similar mating pattern is found in many lek-breeding hylid frogs in which male mating success is mainly determined by chorus attendance.

Genetic Variability of Polish Population of the CapercaillieTetrao urogallus

The Capercaillie is one of the most seriously endangered bird species in Poland. It currently numbers around 650 individuals that live in four isolated populations (Lower Silesian Forest, Janów Lubelski Forest, Carpathians, Augustów Forest). This study investigated genetic variability based on the polymorphism of six microsatellite loci in the surviving Polish populations of the Capercaillie and compares the results with the analogous variability in two large, contiguous populations in Russia. The following parameters were estimated: mean number of alleles per locus, allelic richness, mean effective number of alleles per locus, heterozygosity in each of the populations investigated. Differentiation between pairs of populations was assessed using FST. The results show that despite some inevitable reduction in genetic variability, most of the Polish populations retained a substantial level of microsatellite polymorphism. Only in the population from Janów Lubelski Forest was there a significant reduction in variability, probably due to long isolation and the recent decline. That this population has long been isolated was also confirmed by the pronounced genetic differentiation from the other Polish populations. The Carpathian population of the Capercaillie was found to be genetically structured, and in the Lower Silesian Forest population heterozygosity was low, possibly as a result of the lek mating system and also the dramatic reduction in numbers.

Female choice and male humoral immune response in the lekking great snipe (Gallinago media)

Parasites and diseases constitute major evolutionary forces in many natural populations, and thus having an efficient immune defense to resist infections is crucial for many organisms. Properties of the immune response may also influence mate choice decisions in many animals. Theory predicts several advantages for females when choosing males with superior immune systems. These benefits can be both direct (e.g. increased paternal care and reduced disease transmission) and indirect (good genes). We have investigated female choice with respect to antibody response to two novel antigens in males of a lekking bird, the great snipe (Gallinago media). Because of the lek mating system, female choice probably mainly incurs indirect (genetic) rather than direct benefits. Males responded to vaccination with diphtheria and tetanus toxoids by producing specific antibodies to both antigens. Triggering the immune system had no negative impact on display activities or survival. Males that were chosen by females as mates had on average higher antibody response to the tetanus antigen than their neighbors. We did not, however, find any covariance between the strength of the antibody response and male mating success. (Less)

Thresholds or Comparisons: Mate Choice Criteria And Sexual Selection in a Periodical Cicada, Magicicada Septendecim (Hemiptera: Cicadidae)

AbstractMany insects possess life history characteristics that make them unlikely to use the kinds of relative mate choice criteria implicit in theoretical discussions of leks; thus, many insect mating aggregations are treated differently, as 'swarms' or 'choruses.' Yet periodical cicadas (Magicicada spp.) seem strong candidates for participating in lek mating systems. We present a series of observations and experiments designed to reveal whether there are mating biases in periodical cicadas and whether any biases are most consistent with flexible ('best-of-N 'choice) or fixed (threshold choice) mating criteria. We rule out postcopulatory choice by demonstrating that most females mate once, after which they become sexually unreceptive. In our study, patterns of mating success among actively chorusing males are indistinguishable from random mating, and we uncover no consistent differences between unmated and mated males on the basis of size and song pitch, two criteria that have been associated with Magicicada mating biases in other contexts. Because our results are most consistent with a fixed-threshold choice mechanism, we suggest that Magicicada mating aggregations do not function in a manner similar to vertebrate leks even though they fulfill Bradbury's (1981) lek criteria. Instead, features of Magicicada behavior suggesting female selectivity may arise incidentally from males' and females' unequal tendencies to mate multiply, the resulting superabundance of sexually receptive males, and the high frequency at which females are courted at the onset of mating readiness.

Females lay fewer eggs for males with greater courtship success in a lekking Drosophila

The evolutionary basis for female mate choice in lek mating systems has been a common subject of research in animal behaviour. Because males apparently provide only gametes to females in lekking species, most research has focused on possible indirect (genetic) benefits that females might gain by discriminating among males. Despite the emphasis on indirect benefits, it has been recognized that females in non-resource-based systems such as leks could potentially gain direct benefits via mate choice if males varied in fertilization abilities, for example. Previous evidence has shown that females of a lekking Hawaiian Drosophila, D.grimshawi, vary in fecundity when mated to certain males, and that females possess preferences for vigorously courting males. This study tests the hypothesis that D.grimshawi females gain direct benefits by preferentially mating with more sexually vigorous males. Male courtship vigour (performance of wing and head-under-wing displays) and the consequences of female choice on offspring production were evaluated separately using different females. Unexpectedly, matings involving more vigorously courting males resulted in fewer offspring being produced. Reduced offspring number resulted because females laid fewer eggs when mating with males having greater courtship success. These results are discussed in light of sexual conflict and possible multiple mating by females. Females also demonstrated considerable variation in mating behaviour and behavioural variation was correlated with mating benefits. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.

The paradoxical social system of the DuskyBush-Tanager (Chlorospingus semifuscus): lekking in a nine-primaried oscine?

We studied the behavior of the Dusky Bush-Tanager (Chlorospingus semifuscus; Thraupinae) in southwestern Colombia, where it seems to exhibit singing assemblages resembling leks. A lek mating system would be paradoxical in a genus noted for its active participation in mixed-species flocks, largely insectivorous diet, and stable pair bond. We used the bird's behavior and the relations between fruit availability, its diet, and its participation in mixed flocks to try to explain the social system. We found males singing in dense linear assemblages, regularly spaced along ridgetops, during early morning and late afternoon hours during much of the year, with a peak from May through August. Singing males occupied small circular territories, which usually were reoccupied the next year by the same males. The critical resource is likely the males themselves, although fruit availability may permit them to remain on territories for long periods; nesting areas are apparently far from the ridgetops. Participation in flocks occured year-round but was somewhat reduced during the singing season and in the singing hours. The evidence of pair bonds in this species, in which males participate at least in nest-site selection and feeding of young, excludes the possibility of a lek mating system in the strict sense. Nevertheless, the system of singing linear assemblies appears to have been superimposed upon the typical social system of the genus. This social system is unique in the entire nine-primaried oscine assemblage.

Measures of breeding inequality: a case study in southern elephant seals

Inequality in distribution of resources is a key aspect of evolutionary biology particularly in relation to distribution of mates and copulations. Notwithstanding its important role, inequality is not easily defined, and its measurement is complicated by theoretical and methodological issues. Although the formal treatment of inequality has been mostly limited to the evolution of lek mating system, a methodologically correct approach to measurement of inequality is generally valid for the study of any kind of mating system. In this paper, we analyze inequality in a large set of southern elephant seal (Mirounga leonina) harems. The observed distribution of fertilizations was significantly different from both the expected distribution with equal shares of resources and the expected distribution with equal propensities to acquire resources. We calculate and compare various measures of inequality, observing a wide variation particularly among unbounded and bounded indices. We check the effect of choosing a specific measure of inequality by considering the effect of two aspects of harem socionomy, the number of females in the harem (i.e., the total amount of resources to be shared) and the number of males associated with the harem (i.e., the number of competitors). The choice of a specific measure of inequality had a strong impact on the results obtained and should be considered a critical step in every study of functional and evolutionary correlates of inequality. Unbounded indices showed a strong relationship with both harem size and number of males, while no effect was evident in the analysis of bounded indices. This demonstrates that, in this species, the despotism of the mating system remains high even in large harems and with many competitors, i.e., the worst conditions for monopolization.

WHY DO CALLING MEDFLIES (DIPTERA: TEPHRITIDAE) CLUSTER? ASSESSING THE EMPIRICAL EVIDENCE FOR MODELS OF MEDFLY LEK EVOLUTION

Recent years have seen a proliferation both in theoretical approaches to understanding lek evolution and in empirical work on the lek mating system in the Mediterranean fruit fly. This paper aims to integrate these two lines of research and to identify practical insights of relevance to those engaged in medfly research. We begin by considering the definition of a medfly lek and recognize the existence of male aggregations at two distinct spatial scales: entire trees, or groups of trees within a given habitat; and small areas (ca 30 cm diameter) within the canopy of a given tree. After summarizing the assumptions and predictions of the main candidate models for lek evolution (predation avoidance, hotspot, hotshot and female preferences) we review empirical evidence from previous and ongoing research that is relevant to medfly lek evolution at both spatial scales. Far from being attributable to a single cause, we conclude that the evolution and selective maintenance of lekking behavior in the medfly can be attributed to a complex mosaic of interacting ecological pressures. We recognize that much more empirical work is needed to resolve outstanding questions on medfly lek evolution, and highlight potential benefits from the interaction between pure and applied lines of research on medfly mating behavior.

High frequency of polyandry in a lek mating system

The adaptive significance of polyandry by female birds in the absence of direct benefits remains unclear. We determined the frequencies of polyandrous mating and multiple paternity in the ruff, a lekking shorebird with a genetic dimorphism in male mating behavior. More than half of female ruffs mate with, and have clutches fertilized by, more than one male. Individual females mate with males of both behavioral morphs more often than expected. Polyandrous mating was more likely following copulation interference, but interference was uncommon. The multiple paternity rate of ruffs is the highest known for avian lekking species and for shorebirds. The general hypothesis that pair-bond constraints are the major selective factor favoring multiple mating in birds does not predict our findings. Active genetic diversification, which has been widely dismissed as a functional explanation for polyandrous mating in birds, may apply with respect to the behavioral polymorphism in ruffs because of a Mendelian genetic basis for male behavioral morph determination and aspects of male—male cooperation and female choice. However, rates of multiple paternity in other species of lekking birds are higher than generally realized, and the potential benefits of diversification in general deserve further consideration.

THE VOCAL BEHAVIOUR OF MALE EUROPEAN TREEFROGS (HYLA ARBOREA): IMPLICATIONS FOR INTER- AND INTRASEXUAL SELECTION

[Calls and calling behaviour were studied over two years in a population of individually marked European treefrogs ( Hyla arborea ), a hylid frog with a prolonged breeding season and a lek mating system. A mean daily air temperature of 4.5°C and a nightly water temperature of 9°C were found to represent lower thresholds for nightly calling activity. Large choruses started calling earlier and showed a longer nightly duration of calling activity than small choruses. Temporal properties of advertisement calls were determined mainly by water temperature, which explained up to 88% of the observed variation. Dominant frequency was determined mainly by male body weight, which explained 20% of the observed variance. Within-bout call rate, call duration, pulse period, number of pulses per call and dominant frequency showed little within-male variability, but overall call activity and the number of calls per call bout varied considerably between different recordings of the same individual males. Statistically significant differences between different males were found for withinbout call rate, call duration, number of calls per call bout, number of pulses per call, and dominant frequency. Observed patterns of variability in call properties are discussed in the context of possible implications for female mate choice and male-male recognition., Calls and calling behaviour were studied over two years in a population of individually marked European treefrogs ( Hyla arborea ), a hylid frog with a prolonged breeding season and a lek mating system. A mean daily air temperature of 4.5°C and a nightly water temperature of 9°C were found to represent lower thresholds for nightly calling activity. Large choruses started calling earlier and showed a longer nightly duration of calling activity than small choruses. Temporal properties of advertisement calls were determined mainly by water temperature, which explained up to 88% of the observed variation. Dominant frequency was determined mainly by male body weight, which explained 20% of the observed variance. Within-bout call rate, call duration, pulse period, number of pulses per call and dominant frequency showed little within-male variability, but overall call activity and the number of calls per call bout varied considerably between different recordings of the same individual males. Statistically significant differences between different males were found for withinbout call rate, call duration, number of calls per call bout, number of pulses per call, and dominant frequency. Observed patterns of variability in call properties are discussed in the context of possible implications for female mate choice and male-male recognition.]

Manakins (Pipridae) in Second-Growth and Old-Growth Forests: Patterns of Habitat Use, Movement, and Survival

AbstractWe used capture and recapture data (1985 to 1994) to examine seasonal variation in habitat use, movements within and among habitats, and survival rates of manakins (Manacus candei, Corapipo altera, Pipra mentalis, P. pipra) in northeastern Costa Rica. Manakins were captured in young and old second-growth woodlands in the lowlands and in old-growth forest at approximately 50, 500, and 1,000 m. Manakin species differed in their use of habitats, with old-growth forest species showing large and predictable seasonal variation in capture rates. Corapipo capture rates in lowland (nonbreeding) habitats were greater during the wet season than during the dry season and were greater in old-growth forest than in second growth. Capture rates at 500 m were higher in the dry season. Pipra mentalis capture rates were high in second growth and old growth. Capture rates were higher in the wet season and were correlated with capture rates of Corapipo, indicating that at least some individual P. mentalis migrate along the elevational gradient. P. pipra capture rates were highest at 1,000 m; few individuals descended to lowlands in the wet season. Manacus capture rates were highest in young second growth and did not vary between wet and dry seasons. Use of second-growth habitats by species typically associated with old-growth forests illustrates the value of maintaining a mosaic of habitats to accommodate seasonal changes in use of habitats. Contrary to expectations based on lek mating systems, there was little evidence that movements within habitats (i.e. recapture distances) varied between sexes. Yet, recapture percentages were higher in all species for adult females than males. Adult survival rates were ∼0.75 for Manacus in young second growth, 0.62 for Corapipo in old-growth forest at 50 m and 0.66 at 500 m, and 0.70 for Pipra mentalis in lowland old-growth forest. Results support the suggestion that geographic variation in survival rates may be common in the tropics and illustrate the need for examining survival rates separately by age and sex.

MANAKINS (PIPRIDAE) IN SECOND-GROWTH AND OLD-GROWTH FORESTS: PATTERNS OF HABITAT USE, MOVEMENT, AND SURVIVAL

We used capture and recapture data (1985 to 1994) to examine seasonal variation in habitat use, movements within and among habitats, and survival rates of manakins (Manacus candei, Corapipo altera, Pipra mentalis, P. pipra) in northeastern Costa Rica. Manakins were captured in young and old second-growth woodlands in the lowlands and in old-growth forest at approximately 50, 500, and 1,000 m. Manakin species differed in their use of habitats, with old-growth forest species showing large and predictable seasonal variation in capture rates. Corapipo capture rates in lowland (nonbreeding) habitats were greater during the wet season than during the dry season and were greater in old-growth forest than in second growth. Capture rates at 500 m were higher in the dry season. Pipra mentalis capture rates were high in second growth and old growth. Capture rates were higher in the wet season and were correlated with capture rates of Corapipo, indicating that at least some individual P. mentalis migrate along the elevational gradient. P. pipra capture rates were highest at 1,000 m; few individuals descended to lowlands in the wet season. Manacus capture rates were highest in young second growth and did not vary between wet and dry seasons. Use of second-growth habitats by species typically associated with old-growth forests illustrates the value of maintaining a mosaic of habitats to accommodate seasonal changes in use of habitats. Contrary to expectations based on lek mating systems, there was little evidence that movements within habitats (i.e. recapture distances) varied between sexes. Yet, recapture percentages were higher in all species for adult females than males. Adult survival rates were ∼0.75 for Manacus in young second growth, 0.62 for Corapipo in old-growth forest at 50 m and 0.66 at 500 m, and 0.70 for Pipra mentalis in lowland old-growth forest. Results support the suggestion that geographic variation in survival rates may be common in the tropics and illustrate the need for examining survival rates separately by age and sex.

GEOGRAPHIC SONG VARIATION AND ITS CONSEQUENCES IN THE GOLDEN BOWERBIRD

Abstract Geographic variation in birdsong is known from a variety of taxa, but is especially common and most frequently reported in passerines with resource-based territorial mating systems. To date, relatively little data have been presented on patterns of song variation in species with lek and leklike mating systems. In this paper, we describe geographic song variation in the Golden Bowerbird (Prionodura newtonia) a species with a leklike mating system. We compared recordings of the species advertisement song, collected from five isolated forest blocks from across the species range in northeastern Australia. Golden Bowerbird advertisement song shows marked geographic variation in form. All males within a population sing a song similar to each other, but distinct from that of males from other locations. The song traits important in discriminating between the songs of the different populations were bandwidth, number of peaks, dominant frequency, fundamental frequency, internote interval, and pureness. Dis...

Lek-Like Mating System of the Monogamous Blue-Black Grassquit

AbstractIn this study, we investigated the role of display and mating system of the little known Neotropical Blue-black Grassquit (Volatinia jacarina). Males form aggregations and execute a highly conspicuous display, resembling traditional leks. Number of displaying males declined throughout the study period, though displaying intensity during the season showed no variation. Individual males had significantly different displaying rates and also defended territories of very different sizes, ranging from 13.0 to 72.5 m2, but we found no association between territory sizes and the average displaying rates of the resident males. There also is no association between displaying rates of males and size and vegetation structure of their territories. Four of seven nests were found within male territories and observations indicated that both sexes invest equally in caring for nestlings. Results suggest that the Blue-black Grassquit does not fit into the traditional lek mating system, contrary to what has been proposed in the scarce literature available. However, it is clear that these apparently monogamous birds behave like a lekking species. We speculate about the possibility that aggregation of nesting territories in this species may be due to sexual selection pressures, and suggest that the Blue-black Grassquit may be an ideal candidate to test Wagner's (1997) hidden-lek hypothesis.