Mixed-species Aggregations Research Articles

Collateral damage or a shadow of safety? The effects of signalling heterospecific neighbours on the risks of parasitism and predation.

Although males often display from mixed-species aggregations, the influence of nearby heterospecifics on risks associated with sexual signalling has not been previously examined. We tested whether predation and parasitism risks depend on proximity to heterospecific signallers. Using field playback experiments with calls of two species that often display from the same ponds, túngara frogs and hourglass treefrogs, we tested two hypotheses: (1) calling near heterospecific signallers attractive to eavesdroppers results in increased attention from predatory bats and parasitic midges (collateral damage hypothesis) or (2) calling near heterospecific signallers reduces an individual's predation and parasitism risks, as eavesdroppers are drawn to the heterospecifics (shadow of safety hypothesis). Bat visitation was not affected by calling neighbours. The number of frog-biting midges attracted to hourglass treefrog calls, however, rose threefold when played near túngara calls, supporting the collateral damage hypothesis. We thus show that proximity to heterospecific signallers can drastically alter both the absolute risks of signalling and the relative strengths of pressures from predation and parasitism. Through these mechanisms, interactions between heterospecific guild members are likely to influence the evolution of signalling strategies and the distribution of species at both local and larger scales.

A mechanism mediating inter-individual associations in mixed-species groups

Individuals within groups benefit when they are phenotypically and behaviourally similar. Despite this, mixed-species aggregations are found among a wide range of animal taxa and are known to provide advantages in terms of enhanced foraging efficiency and predator avoidance. However, little is known about individual level interactions within these groups or the mechanisms mediating their structure. Diet-derived chemical cues can mediate within-species associations in fish, but it is not known whether they serve a similar function across species. To investigate this, we created mixed-species groups of sympatric three-spined (Gasterosteus aculeatus) and nine-spined (Pungitius pungitius) sticklebacks and manipulated the diet of the constituent group members. We found that three-spined sticklebacks did not associate more frequently with conspecifics over heterospecifics when all animals received the same diet, suggesting that species-specific cues did not influence association patterns. However, when group members were fed different diets, they interacted with heterospecifics fed on the same diet more than with conspecifics from a different diet treatment. This study demonstrates the importance of chemical cues as a possible mechanism for establishing familiarity, and thereby mediating within-group structure even between individuals in mixed-species aggregations. Understanding these underlying mechanisms has significant implications for our understanding of other social dynamics, including social learning and information transfer. Mixed-species groupings are common among animals, although we have a poor understanding of how these groups are structured, what mediates interactions between group members, and what the function of such groups is. In a study using two co-occurring stickleback species, we show that fish preferred to associate with shoal members fed the same diet as themselves, irrespective of their species. This is most likely mediated by diet-derived chemical cues and may allow fish to avoid detection by predators or forage alongside individuals with similar dietary preferences. Understanding the mechanisms underpinning non-random associations in mixed-species groups has significant implications for our understanding of other social dynamics, including social learning and information transfer.

Sexual differences in responses to cross-species call interference in the green treefrog (Hyla cinerea)

Many species gather in choruses to advertise and search for mates, creating noisy social environments that may impair effective communication. These challenges may be further compounded in mixed-species aggregations, where signals from different species overlap and mate-searching females may perceive heterospecific signals in more attractive relative timing positions. I conducted playback experiments with green treefrogs (Hyla cinerea) to test the effects of cross-species call interference on sexual communication and found that the sexes responded differently to conspecific and heterospecific calls. Females differentiated between call types and preferentially approached the conspecific call, indicating that they were not negatively affected by cross-species call interference. By contrast, males did not differentiate between conspecific and heterospecific calls irrespective of the presented call type and males avoided call overlap and called shortly after the offset of any interfering call. I suggest that the observed sex difference is a function of the time frames that the individual has to evaluate the call before initiating a behavioral response. Slower behavioral responses, like phonotaxis that allows for a repeated sampling of a call during approach, may facilitate finer discrimination. Fast behavioral responses, like timing one’s call relative to the call of a rival, may limit processing and result in higher permissiveness. As a result, similar call timing behavior in response to conspecific and heterospecific signals may be an artifact of strong selection for fast and precise call timing in the conspecific context and may essentially trap males into wasting time and energy interacting with heterospecifics.

Mixed-host aggregations and helminth parasite sharing in an East African wildlife–livestock system

Parasitic infections transmitted between livestock and wildlife pose a significant risk to wildlife conservation efforts and constrain livestock productivity in tropical regions of the world. Gastrointestinal helminths are among the most ubiquitous parasites, and many parasites within this taxon can readily infect a wide range of host species. Factors shaping bidirectional transmission of parasites in wildlife–livestock systems are understudied. In this study, we investigate the prevalence and diversity of helminth infections in an East African community of wild and domestic ungulates. We also identify pairs of host species between which transmission may be possible based on shared parasite taxa, and explore the role of multi-host aggregations in shaping patterns of parasite sharing. Helminth taxa detected included Trichostrongylus, Trichuris, Paramphistomum, Skrjabinema, Strongyloides, Strongylus spp., and other strongyle-type nematodes. We found that nearly 50% of individuals harbored at least one species of helminth, but certain species, such as zebra and impala, exhibited higher prevalence than others. High canopy feeders, like giraffe, had lower prevalence than hosts feeding at medium and low foraging heights. For helminths, patterns of parasite sharing likely emerge from shared space use, which is mediated in part by mixed-species aggregations. The frequency with which host species associated together in mixed-species aggregations was positively correlated with the number of parasite taxa shared. We suggest that variation among species in their tendency to form mixed-species aggregations creates heterogeneity in transmission opportunities, and consequently, parasite sharing across ungulate species. These results enhance our understanding of the role of spatiotemporal relationships among host species in shaping parasite communities in mixed wildlife–livestock grazing systems.

Evaluation of a fishing captain's ability to predict species composition, sizes, and quantities of tunas associated with drifting fish-aggregating devices in the eastern Pacific Ocean

Abstract Experiments were conducted to evaluate a fishing captain's ability to predict species composition, sizes, and quantities of tunas associated with drifting fish-aggregating devices (FADs), before encirclement with a purse-seine net. Operating in the equatorial eastern Pacific Ocean, during 11 May–23 July 2011, Captain Ricardo Diaz detected small quantities of bigeye (Thunnus obesus) and yellowfin (Thunnus albacares) tunas within large FAD-associated aggregations dominated by skipjack tuna (Katsuwonus pelamis). The captain's predictions were significantly related to the actual total catch and catch by species, but not to size categories by species. His predictions of species composition were most accurate when estimates of bigeye and yellowfin tuna were combined. If purse-seine captains are able to make accurate predictions of the proportion of bigeye and yellowfin tunas present in mixed-species aggregations associated with FADs, managers may wish to consider incentives to fishers to reduce the fishing mortality on those species.

Molecular Tools for Species and Sex Identification in the Mixed-Species Flocks of Bean Geese and White-Fronted Geese

Genetic studies on protected species can be difficult, particularly when they form a mixed-species flock with other species. The bean goose (Anser fabalis), which is internationally recognized as a threatened species, was observed to form overwintering foraging flocks with white-fronted goose (Anser albifrons) at agricultural lands to feed on the grains in Korea. Non-invasive samples such as feces and feather that are readily available in their foraging ground can be useful for understanding the structure and composition of populations, but they often require specific experimental conditions due to small amount or low quality of DNA. In this study, we designed sets of primers that would allow efficient molecular identification of species and sex of individuals of bean geese and white-fronted geese. Species-specific primers (WFG-F/BG-F and G-R), developed from ND2 region of mitochondrial DNA, produced PCR products with different sizes which allow easy species identification without further sequencing. Based on published CHD 1 sequences, we designed internal primers (Gsex-F and Gsex-R) for sex determination that can be used in nested PCR after applying P2/P8 primers, and our methods clearly showed high success rate of molecular sexing from non-invasive samples. These molecular tools open the possibilities for genetic studies using non-invasive samples collected from a mixed-species aggregation containing bean geese and white-fronted geese.

Costs and Benefits of Foraging Alone or in Mixed-Species Aggregations for Forster's Terns

Abstract Forster's Terns (Sterna forsteri) often forage alone or within mixed- species foraging aggregations. We investigated the relative costs and benefits of these two foraging strategies. Metrics used to assess differences in strategies included the number of attempts for prey (both successful and missed), capture efficiency, and capture rate. Forster's Terns foraging socially cue on presence and behavior of other aggregating species, especially Snowy Egrets (Egretta thula). Joining aggregations significantly increased their capture rate, but not their capture efficiency, compared to solitarily foraging terns. However, total aggregation size, influenced primarily by the two most abundant species, Laughing Gulls (Larus atricilla) and Snowy Egrets, affected tern behavior. For example, diving terns often collided with Laughing Gulls, causing frequent missed attempts for socially foraging individuals. Thus, large aggregation sizes had a negative effect on foraging success, perhaps because of interference ...

Effects of gear characteristics on the presence of bigeye tuna (Thunnus obesus) in the catches of the purse-seine fishery of the eastern Pacific Ocean

Abstract Lennert-Cody, C. E., Roberts, J. J., and Stephenson, R. J. 2008. Effects of gear characteristics on the presence of bigeye tuna (Thunnus obesus) in the catches of the purse-seine fishery of the eastern Pacific Ocean. – ICES Journal of Marine Science, 65: 970–978. Overfishing of bigeye tuna in the eastern Pacific Ocean has motivated a search for a practical means of reducing the catch of bigeye tuna in mixed species aggregations. To explore the effects of gear characteristics on the catch of bigeye tuna, a classification algorithm for the presence/absence of bigeye tuna catch in purse-seine sets on floating objects is developed, using the tree-based method, random forests. Although the location of the set was the strongest determinant of bigeye tuna catch with these data, bigeye tuna in some areas were more likely to be caught on floating objects with greater underwater depths and with deeper purse-seines. Misclassified sets that caught bigeye tuna were concentrated within certain vessels, suggesting the existence of additional vessel effects. Results indicate that fishers may avoid catching bigeye tuna in some areas by changing the depth of the material hanging from the floating object and the actual fishing depth of the purse-seine, or by moving to other fishing areas. Nonetheless, given the complexity of configuring a purse-seine, and the difficulties associated with monitoring compliance with gear regulations, fishery-wide gear restrictions would be problematic.

Mixed-species aggregations in birds: zenaida doves, Zenaida aurita, respond to the alarm calls of carib grackles, Quiscalus lugubris

Aggregating with heterospecifics may be particularly beneficial for a species that is able to exploit the antipredator behaviour of another. Territorial zenaida doves vigorously exclude conspecific intruders from their territory, but forage with, and acquire novel foraging techniques from, carib grackles. Given that doves associate with no other conspecific than their mate and they have no vocal alarm signals of their own, they might benefit from attending to the conspicuous alarm calls of carib grackles. In the present study, we found that zenaida doves suppressed foraging both in response to a model predator and in response to the sound of grackle alarm vocalizations. Although doves' responses to the predator model also involved moving away from the immediate vicinity, their responses to grackle alarm vocalizations consisted of remaining alert and tail flicking. Together, these results strongly suggest that doves attend to the antipredator behaviour of carib grackles. These findings extend earlier work demonstrating that doves obtain foraging benefits from their association with grackles, to show that they may also obtain predator avoidance benefits.

ANALYSIS OF PATTERNS OF AGGREGATION UNDER COVER OBJECTS IN AN ASSEMBLAGE OF SIX SPECIES OF SNAKES

Use of cover objects for hiding is a well developed behavior in reptiles, including snakes. Snakes sometimes aggregate under cover objects, which may reflect a shortage of suitable cover, very favorable conditions, social attraction, or simply chance. However, most studies of aggregation behavior have been conducted in the laboratory. In this study, I investigated the tendency of six species of snakes to aggregate under rocks in the field in southern Ontario, Canada. Most snakes under rocks were by themselves, but I found single- and mixed-species aggregations of up to four snakes. Although all species were involved in mixed-species aggregations, I did not find all possible combinations of species; no aggregations involved more than two species. Goodness-of-fit tests suggested that the pattern of aggregation sizes was well described by a geometric distribution, implying a nonrandom tendency toward aggregation. Nonetheless, because data were pooled over time, random occurrence of aggregation cannot be ruled out. However, aggregations were clearly nonrandom in another sense: individuals in aggregations tended to be the same size, perhaps indicating size-specific choice of rock and/or fellow snake. Careful field experimentation will be required to test these ideas.

Overriding the oddity effect in mixed-species aggregations: group choice by armored and nonarmored prey

Because ‘‘odd’’ individuals often suffer disproportionately high rates of predation, solitary individuals should join groups whose members are most similar to themselves in appearance. We examined group-choice decisions by individuals in armored and nonarmored species and predicted that either (1) the oddity effect would result in preference for conspecific groups for solitary individuals of both species, or (2) individuals in the armored species would prefer to associate with groups containing individuals of the more vulnerable species. Armored brook sticklebacks (Culaea inconstans) and nonarmored fathead minnows (Pimephales promelas) have the same predators and often occur together in streams. In mixed-species shoals, yellow perch (Perca flavescens) attacked minnows earlier and more often than sticklebacks. We tested whether solitary minnows and sticklebacks preferred to associate with conspecific or heterospecific shoals under conditions of both low and high predation risk. When predation risk was high, minnows preferred to associate with conspecifics over heterospecifics, as predicted by the oddity effect. In contrast, sticklebacks preferentially associated with groups of minnows over groups of conspecifics when predation risk was high. When predation risk was low, solitary individuals of both species preferentially associated with conspecific over heterospecific shoals. Stickleback shoal choices under low-risk conditions may have been influenced by interspecific competition for food. In feeding experiments, minnows were more efficient foragers than sticklebacks, so it should benefit sticklebacks to avoid minnows unless predationriskishigh.Therefore,forarmoredprey,thebenefitsofassociatingwithmorevulnerablepreyappeartooverridethecosts of both the oddity effect and food competition when predation risk is high. Key words: armor, Culaea inconstans, fathead minnows, mixed-species aggregations, oddity effect, Pimephales promelas, predation risk, sticklebacks. [Behav Ecol 14:334‐339 (2003)]

Mixed species aggregations feeding upon herring and sandlance schools in a nearshore archipelago depend on flooding tidal currents

Tidal rips and jets are common features associated with archipelagos and complex coastlines. In habitats where rips and jets develop, energy flow to piscivorous predators is hypothe- sized to be strongly associated with tidal phase due to interactions between currents, plankton, and schooling planktivorous fishes (the 'tidal coupling hypothesis'). This study tests 1 component of the tidal coupling hypothesis, that the feeding activity of piscivorous predators and the availability of planktivorous fishes are both strongly associated with the same tidal phase. During 1994 to 1997, I made visual counts of actively feeding, mixed-species seabird flocks and hydroacoustic measure- ments of the relative abundance and distribution of schooling fishes. Median feeding activity, median backscatter m -1 transect, and median prey encounter probabilities were greatest during the tidal periods Slow flood 1 and Fast flood. Positive feeding anomalies and positive prey-encounter anom- alies were significantly associated with tidal flood phases, but positive backscatter anomalies were not. The results support the tidal-coupling hypothesis, but suggest that changes in the distribution or behavior of schooling fish are as important as, if not more important than, changes in relative fish abundance when determining prey availability and predator foraging-success. The data show that tidal currents can play an important role in structuring nearshore predator-prey interactions.

Diel Habitat Partitioning by Bull Charr and Cutthroat Trout During Fall and Winter in Rocky Mountain Streams

We used underwater observation to determine diel habitat partitioning between bull charr, Salvelinus confluentus, and cutthroat trout, Oncorhynchus clarki, during fall and winter (0.1‐8.3C) in two Rocky Mountain streams that differed in habitat availability. The majority (> 70%) of both species emerged from concealment cover at night, though bull charr exhibited a greater tendency for nocturnal behavior than cutthroat trout. Differences in day and night counts were most pronounced at temperatures< 3C, when very few fish of either species were observed in the water column during the day, but both species were common at night. Both species used concealment cover of large woody debris and boulder substrate crevices in deep pools during the day. At night, fish emerged from cover and habitat use shifted to shallow water with low cover. Microhabitat partitioning among species and size classes occurred at night, cutthroat trout moving into shallower, faster water that was farther from cover compared to bull charr. Smaller fish of both species occupied focal positions in slower, shallower water closer to the substrate than larger fish. Large, mixed-species aggregations also were common in beaver ponds both day and night. High variation in diel and site-specific winter habitat use suggests the need for caution in developing habitat suitability criteria for salmonids based solely on daytime observations or on observations from a few sites. Our results support the need to incorporate nocturnal habitat use and partitioning in studies of salmonid ecology.

Effects of Mixed-species Foraging Groups on the Feeding and Aggression of Juvenile Parrotfishes

Many parrotfishes (Scaridae) co-occur in mixed-species aggregations as juveniles, but diverge in resource use and social structure as adults. Focal observations of three juvenile parrotfishes (Scarus coeruleus, Sparisoma aurofrenatum, and Sparisoma viride) were conducted on inshore patch reefs in the Florida Keys to determine how feeding and aggressive interactions vary with group participation. All three species spent more time in groups than alone, most often in groups of less than ten individuals. Feeding rates were significantly higher for S. viride when foraging in groups than when alone. All species fed most often from Halimeda, and overall diet composition was similar for fish whether feeding in groups or alone. The frequency of aggressive interactions varied with group participation. Focal S. aurofrenatum were more aggressive when in groups than when alone, and both S. aurofrenatum and S. viride were attacked more often by damselfishes when they were alone than when in groups. In contrast, feeding rates, diet breadth, and aggressive interactions of S. coeruleus were less affected by group participation. Small mixed-species aggregations of coral reef fishes may be large enough for individuals to assume some of the benefits of group participation while at the same time avoiding the costs of competition realized in larger groups.

Autumn stopover ecology of the Blackpoll Warbler (Dendroica striata) in thorn scrub forest of the Dominican Republic

We used mist-netting, color-banding, resighting, and behavioral observations to study the autumn stopover ecology of migrating Blackpoll Warblers (Dendroica striata) in coastal thorn scrub forest in the area of Cabo Rojo, Pedernales Province, Dominican Republic. Blackpoll Warblers were the most abundant migrant present in this habitat throughout most of October 1997. Warblers stopping over in this habitat were generally young with moderate to large fat stores. No lean birds (fat score = 0) were captured. Our behavioral observations suggest that Blackpoll Warblers are flexible in terms of social organization, with birds associating in single-species flocks and in mixed-species aggregations, but single birds were also recorded. Foraging activity consisted primarily of gleaning from leaves and was focused on lepidopteran larvae, whose high abundance coincided with Blackpoll Warbler arrival. We suggest that most stopover Blackpoll Warblers were not weakened individuals searching for emergency energy stores but were forced down owing to unfavorable weather conditions for migration; others may have been taking advantage of landfall on the south coast of Hispaniola for daytime rest before continuing across the Caribbean Sea to South America. Coastal thorn scrub forest of Hispaniola appears to be a preferred stopover habitat for a variety of migrants, providing a place to rest and replenish energy reserves following transoceanic flight.

Comparative resource use by juvenile parrotfishes in the Florida Keys

Many parrotfishes (Scaridae) co-occur in mixed-species aggregations as juveniles, but diverge in resource use and social structure as adults. Focal observations of 3 juvenile parrotfishes (Scarus coeruleus, Sparisoma aurofrenatum, Sparisoma viride) were conducted on inshore patch reefs in the Florida Keys to examine feeding rates, food type, habitat use, and aggressive interactions. All species overlapped extensively in their use of space and food. Home ranges physically overlapped, and the proportion of microhabitats present within home ranges was similar for all species. Home range size increased with body size for S. coeruleus and S. aurofrenatum. Diets of all species were extremely similar. All fed selectively from the available foods and fed primarily (>50% total bites) on the calcareous macroalga Halimeda opuntia despite its potentially high energetic costs of procurement, low food value, and predicted avoidance. Focal individuals interacted aggressively with conspecifics, other juvenile parrotfishes, damselfishes, and occasionally grunts and wrasses. S. aurofrenatum and S. viride were most aggressive toward conspecifics. Aggressive interactions with adult parrotfishes were rare. Both Sparisoma spp. were chased more often by damselfishes than any other species. These findings support the growing body of evidence that herbivorous fish do not feed randomly from all potential foods. The aggressive interactions observed among juvenile parrotfishes are likely affecting their use of resources and may act as a precursor to subsequent territoriality as adults.

Cultural transmission of predator recognition in fishes: intraspecific and interspecific learning

Individuals that live in groups may have the opportunity to learn to recognize unfamiliar predators by observing the fright responses of experienced individuals in the group. In intraspecific trials, naive fathead minnows, Pimephales promelas, gave fright responses to chemical stimuli from predatory northern pike, Esox lucius, when paired with pike-experienced conspecifics but not when paired with pike-naive conspecifics. These pike-conditioned minnows retained the fright responses to pike odour when tested alone, indicating that learning had occurred, and transmitted their fright responses to pike-naive minnows in subsequent trials. Brook stickleback, Culaea inconstans, are found in mixed-species aggregations with fathead minnows and are also vulnerable to predation by northern pike. In a series of interspecific tests, pike-naive brook stickleback gave fright responses to chemical stimuli from northern pike when paired with pike-experienced minnows but not when paired with pike-naive minnows. Pike-conditioned stickleback also retained the fright responses when tested alone and subsequently also transmitted the fright responses to pike-naive minnows. Individuals may benefit from observations of the fright responses of conspecifics or heterospecifics by (1) being alerted to the immediate presence of unfamiliar predators and (2) learning to recognize unfamiliar predators as a potential threat.

The Phenology of Four Species of Sargassum at Magnetic Island, Australia

The seasonal variation in density, length, biomass and reproduction for four species of Sargassum living on reefs at Magnetic Island, Queensland, Australia was quantified monthly for a period of 21 months. All our species showed seasonal peaks in size and reproduction. Sargassum tenerrimum, S. fissifolium and S. oligocystum all showed biomass and length peaks in summer (December-February) followed by a late summer peak in reproduction (March-May) while S. linearifolium had earlier peaks in both size (June-September) and reproduction (September-January). Density of adult plants in mixed species aggregations varied unpredictably with no obvious seasonal pattern. Tagging of adult plants suggests that individuals may persist for one of more seasons. Causal hypotheses to explain the observed temporal fluctuations for these species of Sargassum are discussed.

Reproductive behavior of Aplysia californica Cooper: diel patterns, sexual roles and mating aggregations

Reproductive behavior of Aplysia californica Cooper was studied in the field and laboratory. Distinct diel patterns of behavior were found in the field. During the summer > 1 2 of A. california observed at 0300 and 0900 were engaged in reproductive behaviors (precopulatory behavior, copulations, egg-laying); feeding behavior predominated at 1500 and 2100. Relatively little time was spent crawling or being sedentary. This diel behavior pattern was similar during two time periods spanning the sumer peak in A. californica reproduction. A. californica mate in aggregations, which were larger at 0300 and 0900 than at 1500 and 2100. Larger aggregations and aggregations with eggs were more likely to persist to the following day than were small or egg-less aggregations. Despite the relatively high persistence of mating aggregations, individual turnover within the aggregations was high - only ≈ 1 3 of the observed individuals were present in the same aggregation on the following day. Individuals usually joined mating chains as the terminal male, but left from either end or the middle. Mixed-species aggregations of A. californica and the sympatric A. vaccaria Winkler often formed, suggesting that the two species share a common sexual pheromone; however, the two species did not interbreed. A. californica are simultaneous hermaphrodites. The sexual role chosen by an individual was not a function of its mass, relative size compared to its partner, or immediate feeding history. Individuals of some Aplysia species have been reported to specialize in one or the other sexual role; A. californica did not. Egg-laying was associated with subsequent reproduction as a male; reproduction in either role was associated with subsequent egg-laying. The benefits of mating in aggregations probably drive A. californica diel behavior cycles and patterns of social interaction. Major differences in the behavior of different Aplysia species remain to be explained.

Sexual behavior among parasitic Megarhyssa wasps (Hymenoptera: Ichneumonidae)

Male wasps of three sympatric species of Nearctic Megarhyssa (Hymenoptera: Ichneumonidae) typically form mixed-species (61.7%) aggregations composed of up to 28 males over sites of female emergence. Observations of 107 aggregations over two seasons in New York state revealed two male mating strategies: postemergence copulation on the tree surface and preemergence insemination accomplished by male abdominal insertion into the female emergence hole. Insertions by one or more males (as many as ten consecutively but not more than two simultaneously) occurred at 88% of the aggregations, with each inserting for an average of 24.8 min. Insemination as a result of preemergence insertion had a success rate of 83% while postemergence copulation attempts were successful 30% of the time (average duration 61.9 s). Individual male reproductive success was very low and not correlated with size, arrival order at emergence sites, or tenacity at the site. Males frequently aggregated at sites of male emergences as well as those of nonconspecifics, though conspecifics to the emerger ultimately played the major role at aggregations. Male-male aggression in aggregations was not apparent, though jostling occurred during the insertion period and during postemergence copulation attempts.