Showing papers in "Ethology in 2005"

Behavioral Causes and Consequences of Sexual Size Dimorphism

Abstract: (Invited Article) Abstract Sexual size dimorphism (SSD) is widespread and variable among animals. According to the differential equilibrium model, SSD in a given species is expected to result if opposing selection forces equilibrate differently in both sexes. Here I review the factors that affect the evolution of SSD specifically as they relate to behavior. Taking the approach that SSD results as an epiphenomenon from separate but related selection on male and female body size, the advantages and disadvantages of large size in terms of the standard components of individual fitness (mating success, fecundity, viability, growth, foraging success) are discussed to help guiding future research on the subject. This includes a discussion of intra-SSDs. The main conclusions are: (1) Evidence for disadvantages of large body size is still sparse and requires more research. In contrast, evidence for sexual or fecundity selection favoring large body size is overwhelming, so these mechanisms do no longer require special attention, but need to be documented nonetheless to acquire a complete picture. (2) Some hypotheses suggesting that small size is favored are not well investigated at all, because they apply only to some species or restricted situations, may be difficult to study, or have simply been disregarded. Evidence for these cryptic hypotheses is best revealed using experiments under multiple environmental (food, temperature, etc.) stresses with particularly well-suited model species. (3) The evolution of SSD ultimately depends on processes generating variation within as well as between the sexes, so studies should always investigate and report effects on both sexes separately, in addition to size-dependent effects within each sex; within sexes the key issue is whether small individuals under, over- or perfectly compensate their general fitness disadvantage. (4) Tests of several hypotheses should be integrated in case studies of well-suited model species to investigate selection on body size comprehensively. For example, all episodes of sexual selection (mate search, competition, pre- and post-copulatory choice) should be addressed in conjunction. Investigations of size-selective and sex-dependent predation should take the viewpoint of the prey rather than the predator to permit integration of effects throughout prey ontogeny generated by various predators with differing preferences. Comparative studies should also test multiple alternative hypotheses at the same time to permit stronger inference. (5) Experimental behavioral studies of sexual and natural selection should provide selection differentials using the available standard methods. This would allow integration with phenomenological studies of selection and facilitate subsequent meta-analyses, which are very valuable in evaluating general patterns. (6) Comparative phylogenetic studies identifying patterns and phenomenological and experimental studies of model species that investigate particular mechanisms should be integrated, so that macro-evolutionary patterns can be linked to micro-evolutionary processes, which is the central paradigm of evolutionary ecology. (7) A major problem is the general difficulty of separating causes generating a particular body size and SSD over evolutionary time and its consequences for behavior and ecology today, i.e. today's researchers cannot completely avoid this ‘ghost of SSD evolution past’.

Dominance, Status Signals and Coloration in Male Mandrills (Mandrillus sphinx)

Abstract: Where individuals contest access to a resource, escalated physical fighting presents a risk to all involved. The requirement for mechanisms of conflict management has led to the evolution of a variety of decision rules and signals that act to reduce the frequency of aggression during competitive encounters. We examined strategies of conflict management in male mandrills (Mandrillus sphinx) living in two semi-free-ranging groups in Gabon. Adult male mandrills are large (31 kg), with long canines, making the costs of conflict potentially very high. We found that males formed dominance hierarchies, but that male-male relationships were characterized by avoidance, appeasement and ignoring. Fights were rare, but could result in death. Examination of the relationship between dominance and signaling showed that males use facial and gestural signals to communicate dominance and subordinance, avoiding escalated conflict. Male mandrills also possess rank-dependent red coloration on the face, rump and genitalia, and we examined the hypothesis that this coloration acts as a 'badge of status', communicating male fighting ability to other males. If this is the case, then similarity in color should lead to higher dyadic rates of aggression, while males that differ markedly should resolve encounters quickly, with the paler individual retreating. Indeed, appeasement (the 'grin' display), threats, fights and tense 'stand-off' encounters were significantly more frequent between similarly colored males, while clear submission was more frequent where color differences were large. We conclude that male mandrills employ both formal behavioral indicators of dominance and of subordination, and may also use relative brightness of red coloration to facilitate the assessment of individual differences in fighting ability, thereby regulating the degree of costly, escalated conflict between well-armed males.

Differential Behavioural Effects of Silent Bared Teeth Display and Relaxed Open Mouth Display in Chimpanzees (Pan troglodytes)

Abstract: This study examines the behavioural consequences of the silent bared teeth display (SBT) and the relaxed open mouth display (ROM) in the chimpanzee, and discusses functional similarities with smiling and laughing (respectively) in humans. Rates of affinitive behaviour increase (in relation to baseline levels) following SBT, suggesting that SBT is a signal of affinity. ROM is observed primarily during play, and dyadic play bouts are significantly longer when ROM is bidirectional, indicating that it may be a signal of play. Rates of affinitive behaviour also increased after ROM, suggesting that both displays may have a similar ultimate (evolutionary) function – social bonding; this could explain convergence of the two displays in humans.

Testing Problem Solving in Ravens: String-Pulling to Reach Food

Abstract: The aim of our study was to re-examine the acquisition of problem-solving behaviour in ravens: accessing meat suspended from a perch by a string. In contrast to a previous study, here we: (i) controlled for possible effects of fear of the string, competition by dominants, and social learning and (ii) devised a mechanically equivalent but non-intuitive task to test for the possibility of means– end understanding. One-year-old ravens confronted with meat on a string for the first time tried several ways to reach the food. However, five of six birds suddenly performed a coherent sequence of pulling up and stepping on loops of string, essential for solving the problem. Those five birds were also successful in the nonintuitive task where they had to pull down the string to lift the meat. A second group of birds with similar exposure to strings but without any experience in pulling up meat failed the pull-down test. These results support the idea that the ravens behaviour in accessing meat on a string is not only a product of rapid learning but may involve some understanding of cause–effect relation between string, food and certain body parts.

Evolution of Classical Polyandry: Three Steps to Female Emancipation

Abstract: In classical polyandry, sex roles are reversed and a female reproduces with several males, each of whom raises his offspring with little or no help from her. This mating system occurs in some fishes and birds, and it is of great interest in relation to parental investment, sex role and sexual selection theory. The evolution of classical polyandry, however, is debated and not well understood. It is here suggested to generally take place in three main steps. (1) First evolves male care for eggs, for reasons that differ between fishes and birds. (2) Second, a female becomes able to lay more eggs than a male can accommodate. This can happen, for example, by evolution of male pregnancy or smaller body size, or by female production of more or larger eggs, made possible by larger female body size or more food. Polyandry in several taxa is associated with shift to a habitat rich in food during the breeding season, to novel specialised foraging methods, or to both. A favourable food situation may be crucial for evolution of classical polyandry. (3) In step three, females compete to lay two or more clutches in sequence for different males. Successful polyandrous females obtain more offspring, spreading traits that enhance success in competition over males. Step three may be most likely in species with small body size, for reasons of reproductive constraints and seasonality. Evolution of classical polyandry appears to have followed these steps in shorebirds, coucals and pipefishes, but the reasons why certain species differ from their close phylogenetic relatives in being polyandrous are far from clear. Behavioural and ecological studies of additional species, and detailed phylogenies of taxa with diverse mating systems including polyandry, are needed for testing these ideas.

Consistency in Context-specific Measures of Shyness and Boldness in Rainbow Trout, Oncorhynchus mykiss

Abstract: Shyness and boldness has been considered a fundamental axis of human behavioural variation. At the extreme ends of this behavioural continuum subjects vary from being bold and assertive to shy and timid. Analogous patterns of individual variation have been noted in a number of species including fish. There has been debate on the nature of this continuum as to whether it depends on context. That is, whether it is domain-general (as in humans), or context-specific. The purpose of our study was to test if shyness and boldness depends on context in rainbow trout, Oncorhynchus mykiss and to this end we estimated boldness in five different situations. Our data provide evidence of a shy-bold behavioural syndrome in rainbow trout. Bold trout tended to be bold in four situations when the context was similar (when the context concerned foraging). However, in a different context, exploring a swim flume, the ranking was entirely different. We suggest that shyness and boldness depends on context in rainbow trout.

Intra‐ and Intersexual Selection for Multiple Traits in the Peacock (Pavo cristatus)

Abstract: Animal communication involves a multitude of signals ranging from morphological to behavioural traits. In spite of the diversity of traits used in animal signalling, most studies of sexual selection have focused on single male traits. Moreover, the two forces of sexual selection (male–male competition and female preference) may target different traits and favour the diversification of male signalling. Still, little is known on the combined effects of intra- and intersexual selection on the evolution of multiple signals. The peacock is often cited as one of the best examples of the strength of sexual selection in producing exaggerated traits. Here, we investigated traits under intra- and intersexual selection in a population of free-ranging common peafowl. Peacocks with longer trains and tarsi were more likely to establish a display territory in a central position within the lek and had a higher number of intrusions and agonistic interactions. These traits appeared therefore to be under intrasexual selection. Female selection was assessed as the number of copulations. Mating success was positively correlated with behavioural traits (display activity) and with train ornamentation (number and density of ocelli) suggesting that females use multiple cues during mate selection. Therefore, intraand intersexual selection seem to operate on different sets of traits. Overall, our results stress the role of multiple receivers on the evolution of multiple signals.

On the Relationship between Herbaceous Cover and Vigilance Activity of Degus (Octodon degus)

Abstract: A number of studies demonstrate that plant cover provides prey animals with refuges to decrease vulnerability to predators. However, others suggest plant cover to visually obstruct detection of predators or conspecifics. We suggest these seemingly conflicting results can, to some extent, be resolved if overhead vs. lateral cover are distinguished. We recorded seasonal variation in vigilance activity of a natural population of degus (Octodon degus), a diurnal, semi-subterranean and social rodent from central Chile. We used these data to determine whether cover provided by herbaceous vegetation is mostly obstructive. The height of herbaceous vegetation in the habitat of degus varied seasonally, and the ability of degus (estimated from human observers) to detect potential predators decreased when herbaceous vegetation was high. This effect was more important for degus using quadruped postures and when dealing with terrestrial simulated predators. Accordingly, degus adjusted the quality rather than the quantity of their vigilance activity: male and female degus allocated similarly more time to bipedal vigilance when the height of herbs was high. Such increase in bipedal vigilance seemed to occur at the expense of quadruped vigilance instead of foraging time. Collectively, these results support the hypothesis that cover of herbaceous vegetation is mostly obstructive to degus when active above ground, a finding that contrasts with previous evidence supporting that shrub cover provides refuges against predators. The differential effects of shrubs and herbs on degu vigilance are likely linked to differences in the costs and benefits associated with each cover type. For degus, shrubs may provide more overhead (protective) than lateral (obstructive) cover.

How to Repair Relationships – Reconciliation in Wild Chimpanzees (Pan troglodytes)

Abstract: Reconciliation appears to repair the relationships of former opponents after being disturbed by aggressive interactions. Despite a consensus about the benefit of reconciliation, how former opponents achieve this benefit remains unclear. Variation within reconciliation is evident in many species, but understanding what causes the variation has been mostly neglected until now. We collected 178 events of reconciliation of both sexes in a community of wild chimpanzees (Pan troglodytes) in the Tai National Park, Cote d'Ivoire. Our data provide evidence for the relationship-repair function of reconciliation, as aggression disturbed tolerance levels among former opponents and reconciliation restored tolerance to normal levels again. Partners with highly beneficial relationships reconciled more often compared with partners of low mutual benefit. Latency and duration of reconciliation varied in combination, such that short reconciliations were initiated soon after the conflict, while long reconciliations were initiated later. Latency increased with the risk of further aggression, while duration decreased when costs were incurred from interruption of beneficial activities. In contrast, the complexity of reconciliation varied according to the intensity of the preceding conflict, such that reconciliation was more complex after more intense conflicts. Our results suggest that relationships between opponents are increasingly disturbed with increasing conflict intensity and reconciliation repairs all relationships independent of their relationship value. We propose that the function of reconciliation is to reduce the disturbance created by aggression, but the more frequent the reconciliation, the more beneficial it is for former opponents.

Memory of Social Partners in Hermit Crab Dominance

Abstract: We investigated the possibility that invertebrates recognize conspecific individuals by studying dominance relationships in the long-clawed hermit crab, Pagurus longicarpus. We conducted three sets of laboratory experiments to define the time limits for acquiring and maintaining memory of an individual opponent. The results reveal two characteristics that make individual recognition in this species different from standard associative learning tasks. Firstly, crabs do not require training over many repeated trials; rather, they show evidence of recognition after a single 30-min exposure to a stimulus animal. Secondly, memory lasts for up to 4 d of isolation without reinforcement. A third interesting feature of individual recognition in this species is that familiar opponents are recognized even before the formation of a stable hierarchical rank. That is, recognition seems to be relatively independent of repeated wins (rewards) or losses (punishments) in a dominance hierarchy. The experimental protocol allowed us to show that this species is able to classify conspecifics into two 'heterogeneous subgroups', i.e. familiar vs. unfamiliar individuals, but not to discriminate one individual of a group from every other conspecific from 'a unique set of cues defining that individual'. In other words, we demonstrated a 'binary' - and not a 'true' - individual recognition. However, 1 d of interactions with different crabs did not erase the memory of a former rival, suggesting that P. longicarpus uses a system of social partner discrimination more refined than previously shown.

Females Mated without Sperm Transfer Maintain High Sexual Receptivity in the Wolf Spider Schizocosa malitiosa

Abstract: The mating of the Neotropical lycosid Schizocosa malitiosa is long and complex, involving intense genital stimulation and copulatory courtship. This suggests functions other than just insemination. Previous data indicated that mated females of this species are less sexually receptive than virgins. We hypothesise that copulatory characteristics presented by males during prolonged copulations could be responsible for subsequent female sexual reluctance, and may be selected by cryptic female choice. Our objective was to examine the influence of copulatory behaviour on subsequent female sexual receptivity in S. malitiosa, isolating it from the effects of sperm transfer per se. For this purpose, we obtained males without sperm in their copulatory organs (palpal bulbs), and prevented them from charging their palps by sealing their genital pores immediately after their last moult (treated males). Virgin females were separated into three groups: (i) females exposed once to normal males, (ii) females exposed twice to normal males, and (iii) females exposed first to treated and second to normal males. The results showed that, 3 d after their first mating, females first mated with untreated males were frequently refractory to remating, whereas all those first mated with treated males were receptive. Copulations performed by treated males showed some differences from those performed by normal males, but maintained the basic behavioural pattern with abundant sexual stimulation. The presence of sperm fluids in the female receptacles appears to be the most likely factor generating female remating reluctance. Males may manipulate female responses using receptivity inhibiting substances in their sperm, like those described for insects. Females would first ensure sperm supply, becoming more choosy afterwards. All females, whether mated once or twice, generated similar numbers of progeny, indicating no relationship between number of matings and number of spiderlings.

Status and Reproduction in Humans: New Evidence for the Validity of Evolutionary Explanations on Basis of a University Sample

Abstract: A strong positive relationship between reproductive success (offspring count) and status (position in the institutional hierarchy) is demonstrated in a contemporary sample of male university employees (n ¼ 2693). Male academics in leading positions have more children than do other male employees. In female university employees (n ¼ 2073), a negative relationship between status and reproductive success was found, but only if childless women were included in the analysis. Although a positive relationship between male status and offspring count has been predicted by evolutionary theory and was found in animal species and traditional human societies, in modern societies most of the studies found no or even a negative relationship between status and reproductive success in males. We suggest that status may be a more important dimension for particular subsamples of modern society than for samples representing entire societies, so that associations might actually differ among subsamples. We suggest that analyses on a small and rather uniform level using modern large-scale hierarchical organizations (such as universities) are candidates for the investigation of appropriate society subsets. Our results may stress the importance of evolutionary predictions and may be of relevance for theoretical and empirical considerations at the levels of economics and administration.

Threat-sensitive responses to predator attacks in a damselfly

Abstract: The threat sensitivity hypothesis predicts that prey species assess and adjust their behavior flexibly in accordance with the magnitude of the threat imposed by a predator. We tested this hypothesis with regard to escape behavior and thanatosis (feigning of death to escape predation) in larvae of the damselfly Ischnura elegans. We manipulated the perceived predation threat of the larvae by changing three factors: lamellae autotomy (an escape strategy where animals sacrifice a body part when grasped by a predator; lamellae present or absent), kairomone type (odors released by predators; control, dragonfly kairomones or fish kairomones), and population of origin (fishpond or fishless pond). We demonstrated that thanatosis increased survival both when confronted with dragonfly and fish predators. We could show, for the first time, costs of past autotomy to be predator-dependent: larvae without lamellae suffered higher predation mortality but only in the presence of a dragonfly predator and not in the presence of a fish predator. This is in accordance with the observed reduced escape speed of larvae after autotomy, which may affect escape probability toward dragonfly predators but not to the very fast fish predators. Unexpectedly, kairomone type did not affect the escape response of the larvae. In accordance with the threat sensitivity hypothesis, after an unsuccessful attack, larvae without lamellae had a higher frequency to enter thanatosis than larvae with lamellae and larvae from the fishpond showed longer thanatosis durations than larvae from the fishless pond. Consistent with the hypothesis, the reaction of the larvae to a simulated attack depended jointly on lamellae status and population. In fishless ponds, larvae with lamellae swam away more frequently than larvae without lamellae; in fishponds both groups almost never swam away and relied mostly upon immobility. Given the obvious benefits of adaptively varying escape responses we hypothesize this threat sensitivity to be widespread. Moreover, we argue that former inconsistencies between studies with regard to escape behavior may have been partly because of such adaptive variation.

Non‐Vocal Shaping of Avian Song Development: Parallels to Human Speech Development

Abstract: Vocal development in young male cowbirds (Molothrus ater) is sensitive to acoustical stimulation from males, but also to social feedback from female cowbirds, even though females do not sing. Juvenile males show different vocal trajectories if housed with local or distant population females. The major goal of the present study was to identify differences in the form and timing of non-vocal cues from females during the period in early spring when juvenile males begin to sing stereotyped song and to finalize their repertoires. We housed juvenile males with either local or distant population females and no adult males. We found significant differences between the two groups of females in the use of wing stroking and in male reactions to wing strokes and gapes. There were also differences between the groups in male song performance. To understand further the potential consequences of these differences, we correlated measures of male and female responsiveness to results reported in Smith et al. (2000) on vocal ontogeny and song potency. We found that wing stroking by females was associated with a faster rate of song development and tended to relate to differences in song potency. The non-vocal shaping seen here may represent a general mechanism for the development of vocal communication, as similar processes influence phonological development in human infants.

An investigation of assessment games during fallow deer fights

Abstract: An improved understanding of the decision rules used by competing animals can be achieved by examining both the temporal structure and display rate of competitors during a contest. Current models of animal competition make different predictions regarding the behaviour of competing animals and the present study evaluates the predictions of three such models, the energetic war of attrition (eWOA), the sequential assessment game (SAG) and the cumulative assessment model (CAM) by applying them to the fighting behaviour of male fallow deer (Dama dama L.). There was no difference in rate at which the jump clash and backward push were recorded over fight duration; therefore, in terms of the temporal distribution of behavioural acts within fights, the jump clash and backward push conformed to the predictions of the SAG. There was a difference between winners and losers of fights for the frequency that the jump clash and backward push were recorded consistent with both the SAG and CAM. Analysis of bout duration showed that there was a decrease in the duration of subsequent bouts of fighting; this is only permitted under eWOA. In so far as current assessment models permit interpretation of the data, our results meet only a limited number of predictions of any one model. Given the difficulty in interpreting our data within the context of current assessment models, recommendations for the development of more complex models are presented.

Physiological Costs of Mate Guarding in the Japanese Beetle (Popillia japonica Newman)

Abstract: Males of many insects directly defend their mates from rival males (i.e. mate guard) as a way to avoid sperm competition and thus increase their reproductive success. However, mate guarding may have associated costs for these males. We examined costs of mate guarding in Japanese beetles (Popillia japonica), a pest species which exhibits post-copulatory mate guarding during which the guarding male cannot feed. In this species, food provides both energy and water for thermoregulation. Consequently, we focused on possible thermoregulatory and energetic costs of their mate guarding. In a field study, we found that guarding males had significantly higher thoracic temperatures than non-guarding males, indicating a difference in their ability and/or need to thermoregulate. Paired males had significantly lower water levels than single males in the morning and evening, but not in the afternoon. In the laboratory, we found that mate-guarding duration was significantly shorter at higher ambient temperature than at lower temperature, and males that had been starved guarded for less time than males that had not been starved. Our results suggest that because guarding males are unable to feed, they suffer energetic and thermoregulatory costs that appear to limit the amount of time that they can guard a female.

Ontogeny of Acoustic and Feeding Behaviour in the Grey Gurnard, Eutrigla gurnardus

Abstract: Although sound production in teleost fish is often associated with territorial behaviour, little is known of fish acoustic behaviour in other agonistic contexts such as competitive feeding and how it changes during ontogeny. The grey gurnard, Eutrigla gurnardus, frequently emits knock and grunt sounds during competitive feeding and seems to adopt both contest and scramble tactics under defensible resource conditions. Here we examine, for the first time, the effect of fish size on sound production and agonistic behaviour during competitive feeding. We have made sound (alone) and video (synchronized image and sound) recordings of grey gurnards during competitive feeding interactions. Experimental fish ranged from small juveniles to large adults and were grouped in four size classes: 10–15, 15–20, 25–30 and 30–40 cm in total length. We show that, in this species, both sound production and feeding behaviour change with fish size. Sound production rate decreased in larger fish. Sound duration, pulse duration and the number of pulses increased whereas the peak frequency decreased with fish size, in both sound types (knocks and grunts). Interaction rate and the frequency of agonistic behaviour decreased with increasing fish size during competitive feeding sessions. The proportion of feeding interactions accompanied by sound production was similar in all size classes. However, the proportion of interactions accompanied by knocks (less aggressive sounds) and by grunts (more aggressive) increased and decreased with fish size, respectively. Taken together, these results suggest that smaller grey gurnards compete for food by contest tactics whereas larger specimens predominantly scramble for food, probably because body size gives an advantage in locating, capturing and handling prey. We further suggest that sounds emitted during feeding may potentially give information on the motivation and ability of the individual to compete for food resources.

Sex, rank and age differences in the Japanese macaque (Macaca fuscata yakui) participation in inter-group encounters

Abstract: In many species interactions among group are often characterized by agonistic behaviour. Although animals may participate in inter-group encounters in different ways, depending on their energetic requirements, reproductive tactics, and/or developmental stage, the proximate causes affecting an animal's participation in inter-group encounters are still poorly understood. Indeed, many studies have analysed the behaviour of males and females during inter-group encounters without considering the importance of additional factors (e.g. rank). This study focuses on wild non-provisioned Japanese macaques (Macaca fuscata yakui) living on Yakushima Island, Japan. It aims to determine how monkeys of different sex, age, and rank behave during inter-group encounters and it discusses the implications and consequences of their behaviour on group composition and male dispersal. Males participated significantly more than females in inter-group encounters, by displaying more aggressive or affiliative behaviour. High-ranking and/or adult males were more aggressive than low-ranking and/or subadult males during encounters occurring in the mating season and they also showed more herding behaviour. This trend was not found in inter-group encounters occurring during the non-mating season. Finally, males which then emigrated to new groups were low-ranking and/or subadult individuals. Those males displayed more affiliative behaviour towards foreign males than males which did emigrate. These data indicate that in non-territorial species with male dominance over female and high competition for mating partners males play an active, and often aggressive, role during inter-group encounter while female participation is scarce. Factors such as age, rank and period of the year (in seasonally breeding species) have to be taken into considerations when analysing interactions between groups and their effects on group composition and social behaviour.

Cooperative Breeding and Group Structure in the Lake Tanganyika Cichlid Neolamprologus savoryi

Abstract: As yet, cooperative breeding has been described only for some fish species. However, evidence is accumulating that it is widespread among Lake Tanganyika cichlids. We studied the cooperative breeding system of the substrate breeding cichlid Neolamprologus savoryi. Breeding groups typically consisted of a large breeding male with one to four breeding females and three to 33 helpers (mean group size: 14.3 members). Group size was significantly related to breeding male and female body sizes, and larger males had more breeding females and larger sized male helpers. The size of the largest female in the group was positively related to the number and sizes of secondary breeding females and female helpers. In case of multiple breeding females, these females usually divided the group's territory into sub-territories, each with its own helpers (subgroups). Interspersed between groups, independent fish were detected defending an individual shelter (4.4% of all fish). In 9% of the groups no breeding female was present. All group members participated in territory defence and maintenance, and showed submissive behaviours to larger group members. As expected, the level of between-subgroup conflicts was high compared with the level of within-subgroup conflicts. We compare these results with data available from other cooperatively breeding fishes.

Limits to Male Copulation Frequency: Sexual Cannibalism and Sterility in St Andrew's Cross Spiders (Araneae, Araneidae)

Abstract: Sexual cannibalism is common among orb-web spiders and may limit male copulation frequency. Each copulation by male St Andrew's Cross spiders (Argiope keyserlingi) involves the transfer of sperm from one pedipalp only. Almost half of the males survive their first copulation, but all of the surviving males are cannibalized when they copulate with the other pedipalp. We investigated why males cannot copulate more than twice. Experimentally fatigued males were not cannibalized more frequently than control males. Experimental removal of one pedipalp in virgin males did not increase cannibalism during their first copulation, but the surviving males were unable to copulate with a subsequent female, suggesting they cannot use a pedipalp more than once. Un-manipulated males always inserted their unused pedipalp during their second copulation. Sperm counts from males preserved immediately after copulation and from males maintained for an additional 3 wk show that used pedipalps are not replenished over such a period.

Seasonal Variation in Response to Neighbors and Strangers by a Territorial Songbird

Abstract: Reduced aggression toward territorial neighbors, termed the ‘dear-enemy’ effect, is thought to arise because territorial animals benefit by avoiding contests with neighbors with whom they have already established relationships. The dear-enemy effect has been described in many taxa, but few studies have considered whether or not neighbors’ relationships are affected by changes in the social environment. In this study, I tested whether Carolina wrens, Thryothorus ludovicianus, behaviorally discriminate between neighbors and strangers in two different social environments: in spring when territories have been established for several months, and in fall when an influx of new birds claiming territories might de-stabilize wren neighborhoods. Comparisons of responses of territorial males to playbacks of songs from neighbors and strangers showed that Carolina wrens show the dear-enemy effect in spring, but not in fall in this design. The apparent lack of a differential response to neighbors and strangers in fall might be due to a reduction in aggression toward strangers. This study provides evidence that seasonal changes in the dear-enemy effect coincide with seasonal changes in the social environment.

Correlations between Ontogenetic Change in Color Pattern and Antipredator Behavior in the Racer, Coluber constrictor

Abstract: Differences in snake color pattern have been demonstrated to affect behaviors involved in antipredator defense. Snakes with blotched or banded color patterns are concealed when not moving, and tend to rely on concealment and aggression for defense. In contrast, snakes with uniform or striped color patterns are easily seen when stationary, but their speed and direction are difficult to track when moving. They tend to rely on flight for protection. Some snake taxa exhibit ontogenetic change in color pattern, but the behavioral consequences of this change have not been investigated. I present results of a behavioral study in the racer, Coluber constrictor, which has a blotched juvenile color pattern but is uniformly colored as an adult. Hatchling racers were significantly more likely than adults to show aggressive behavior when confronted with a model predator, whereas adults were more likely to flee. This supports the hypothesis that changes in behavior and color pattern are correlated in this species to provide effective antipredator defense at different stages of life history. I also examined sprint speed, which may be an important factor in antipredator defense. Juvenile and adult racers showed a similar relationship between length and speed, a pattern also seen in other species that lack color change. This result suggests that sprint speed is not a causal factor in the evolution of ontogenetic color change.

Prior Residence Influences Contest Outcome in Flocks of Non-Breeding Birds

Abstract: We sought to determine whether early arrival was a determinant of contest outcome in loosely organized, non-breeding flocks of birds. In White-throated Sparrows (Zonotrichia albicollis) arrival date during autumn migration, i.e. within-year prior residence, was a significant determinant of contest outcome for those birds that were not present on the study site in previous years. To determine whether the advantage of early arrival was due to prior residence per se, as opposed to some correlate of arrival date (e.g. condition), we experimentally delayed the arrival of 60 migrants. We found a significant effect of the delay: the outcome of contests between naturally arriving (control) birds and experimentally delayed birds was significantly related to the difference between the control bird's natural arrival date and the experimental bird's delayed arrival date. Thus, prior residence per se, and not some correlate of arrival date, had a significant effect on a naive individual's ability to win contests. Interestingly, arrival date had no effect on contest outcome among birds that had wintered on the site in previous years. Because a prior residence advantage accumulates in a time-dependent manner, our results suggest that fighting ability or perceived resource value increases with site familiarity. Thus, there may be selection on arrival date and site-faithfulness as behavioral strategies to increase access to resources.

Testing the Functions of Detritus Stabilimenta in Webs of Cyclosa fililineata and Cyclosa morretes (Araneae: Araneidae): Do They Attract Prey or Reduce the Risk of Predation?

Abstract: Spiders of the genus Cyclosa often add prey remains and other debris to their orb-webs. The function of silk decorations is generally associated with defense against predators or with the attraction of prey, but few studies have focused on stabilimenta containing detritus. In this study, we used artificial webs with and without the detritus stabilimenta of two species of Cyclosa to investigate whether these structures increase the number of insects intercepted. Artificial models of spiders and stabilimenta were used to compare the frequency of attacks against different shapes. We also conducted choice experiments in laboratory to determine whether detritus columns attracted Drosophila melanogaster (Diptera: Drosophilidae) and Trigona angustula (Hymenoptera: Apidae, Meliponinae) to the webs. The frequency of interception in artificial webs with a stabilimentum was similar to that of webs without such structure. The taxonomic composition and biomass of insects were also similar in both types of artificial webs. The choice experiments showed no significant tendency in attraction to webs with a stabilimentum. However, models of spiders were attacked at a higher frequency than those simulating detritus columns and silk decorations. These findings argue against the prey attraction hypothesis and suggest that the addition of stabilimenta to webs of Cyclosa could reduce the intensity of predation, possibly by disrupting the image of the spider's outline.

Snake Species Discrimination by Wild Bonnet Macaques (Macaca radiata)

Abstract: Wild bonnet macaques (Macaca radiata) were studied in southern India to assess their ability to discriminate non-venomous, venomous and predatory snakes. Realistic snake models were presented to eight troops of bonnet macaques at feeding stations and their behavior was video-recorded 3 min before and 3 min after snake exposure. Snakes presented were: (1) venomous Indian cobra (Naja naja) displaying an open hood with 'eyespots'; (2) venomous common Indian krait (Bungarus caeruleus); (3) non-venomous green keelback (Macropisthadan plumbicolor); (4) non-venomous rat snake (Ptyas mucosus); and (5) Indian python (Python molurus) which preys on macaques. Latencies to detect and react to the snakes were evaluated to determine initial responsiveness. Longer-term assessment was measured as the percentage of time individuals looked at the snakes and monitored the activity of nearby individuals before and after snake detection. All snake models engendered caution and maintenance of a safe distance. Alarm calling occurred only during python presentations. The cobra engendered a startle response or running in the largest percentage of individuals after its detection, whereas the rat snake and python elicited bipedal standing or ambulating to monitor the snakes. We also examined the influence of age on snake recognition. Juveniles and subadults looked at the cobra, krait, and python for a larger percentage of time than adults did; albeit, adults looked at the python substantially longer than at the other snakes. Age differences in behavior suggest that, with the exception of the python, repeated experience with snakes in the wild moderates excitability, consistent with the likely threat of envenomation.

Light‐Dependent Shift in Bullfrog Tadpole Magnetic Compass Orientation: Evidence for a Common Magnetoreception Mechanism in Anuran and Urodele Amphibians

Abstract: Previous studies have demonstrated the presence of a light-dependent magnetic compass in a urodele amphibian, the eastern red-spotted newt Notophthalmus viridescens, mediated by extraocular photoreceptors located in or near the pineal organ. Newts tested under long-wavelength (‡500 nm) light exhibited a 90� shift in the direction of orientation relative to newts tested under full spectrum (white) or short-wavelength light. Here we report that bullfrog tadpoles Rana catesbeiana (an anuran amphibian) exhibit a 90� shift in the direction of magnetic compass orientation under long-wavelength (‡500 nm) light similar to that observed in newts, suggesting that a common light-dependent mechanism mediates these responses. These findings suggest that a lightdependent magnetic compass may have been the ancestral state in this group of vertebrates.

The Brief Piping Signal of the Honey Bee: Begging Call or Stop Signal?

Abstract: For over 40 yr, investigators have recognized that the brief piping signal plays a role in the foraging operation of a honey bee colony. The function of this signal, however, remains uncertain. The main objective of this study was to determine whether, under normal foraging conditions, bees following waggle dancers produce brief piping signals to beg nectar samples from the dancers. We made observations on waggle dancers and their followers in an undisturbed colony whose foragers gathered nectar and pollen from flowers. We found that waggle dancers do often receive brief piping signals, that the bees producing these signals are generally dance followers, and that these signals increase a waggle dancer's tendency to stop dancing. We also found, however, that the brief piping signal is clearly not a begging call; 0 of 41 waggle dancers that received a piping signal from a dance follower gave a nectar sample to the bee that produced the signal. Our results support the hypothesis that the brief piping signal is a stop signal; it serves to shut off waggle dancing. But why some dance followers pipe the dancer they are following, thereby inhibiting her dancing, remains unclear and warrants further investigation.

Predicting Herbivore Feeding Times

Abstract: An understanding of animal time budgets is crucial to behavioural biology. Although many studies have analysed time budgets of individual species, only a few have made interspecific comparisons. Here we take an interspecific look at one part of the time budget, feeding time. We hypothesize that feeding time can be predicted by the amount of time an animal needs to reach satiation. This time should be equal to the ratio of handling time to digestion time. For 19 herbivorous species from insects to mammals, we calculate this ratio and compare it to the observed feeding time. The mean difference between calculated and observed values is small (a half hour per 24 h-day), indicating that herbivore feeding times can often be approximated by the ratio of handling time to digestion time. We make three points concerning the time allocated to feeding in herbivores based on this interspecific comparison. First, our analysis suggests that herbivores often feed to satiation, which could mean that they are often released from time constraints. It is also possible, however, that while herbivores have enough time to reach satiation, they do not necessarily have sufficient time to choose the most desirable diet. Wilson's principle of stringency theoretically supports the former interpretation. It suggests that animals experience periods in their life in which they are time-constrained but that these periods are the exception rather than the rule. Most optimal foraging studies have assumed the opposite. The second point of this paper is therefore a recommendation: to consider the possibility that animals may often be released from time constraints. The third and final point is that feeding time is independent of body mass in our analysis. This is because handling time scales with body mass according to a parameter that is similar to the one for digestion time, and feeding time can be approximated by the ratio of handling time to digestion time.

Wall Lizards Modulate Refuge Use through Continuous Assessment of Predation Risk Level

Abstract: Prey species might use several possible ways to assess predation risk when encountering a predator. Animals may consider the risk level estimated in a first encounter to remain unchanged across subsequent encounters (fixed risk response), or they may update and change their responses across encounters in accordance with short-term changes in risk levels (flexible risk response). We examined in the field how wall lizards assess risk level by analyzing time spent in refuges after simulated predator attacks. We first examined how risk was assessed when multiple consecutive sources of risk were present simultaneously. The results suggest that wall lizards assess risk based on multiple cues, such as approach speed, directness, and persistence (measured as the distance of the predator to their refuge after an attack). When risk was high lizards remained longer in their refuges. The first decision to appear partly from the refuge depended on both approach speed and persistence, whereas the decision to emerge completely depended only on persistence and not on approach speed. This suggests that wall lizards update information on predator threat and adjusted their emergence accordingly. In a second experiment, we analyzed how short-term changes in risk level of successive attacks affected refuge use. Successive emergence times varied as a function of current risk level of each repeated attack, independently of the risk level of previous attacks. This indicated that lizards could track short-term changes in risk level through time and modify their initial responses when required. Fine adjustments of refuge use may help lizards to minimize costs of refuge use in unfavorable and variable environments where antipredatory responses are costly.

German Yellowjacket (Vespula germanica) Foragers Use Odors Inside the Nest to Find Carbohydrate Food Sources

Abstract: Prior work has shown that yellowjacket wasps remember food odors and use them as cues when foraging. There is also evidence they have mechanisms to recruit nest mates to highly rewarding food sources, as naive individuals are more likely to go to food sources with scents similar to those visited by nest mates. We asked whether recruitment requires behavioral stimulation by returning foragers, as in honey bees, or if sampling the food source inside the nest is sufficient. We tested this by eliminating the behavior of returning foragers by inserting a scented sugar solution directly into a Vespula germanica nest. Exiting foragers were given a choice of the test scent and a control scent. Wasps were more likely to choose the test scent. We conclude that behavioral interactions with returning foragers are not necessary to stimulate nest mates to associate an odor with a food source and search for a resource bearing that odor, and that experience with the scented reward inside the nest is sufficient to achieve this result.