Social influences on territorial signaling in male greater sac-winged bats

Acoustic territorial displays are common among birds but comparatively rare among mammals. An exceptionally vocal mammal well-known for its elaborate territorial displays is the polygynous greater sac-winged bat, Saccopteryx bilineata. Male S. bilineata are often philopatric and establish small territories in their birth colony in which females can roost during the day. During territorial defense, males produce complex territorial songs that are learned through vocal imitation. Territorial songs are mainly produced at dawn and dusk. We studied social influences on male vocal activity and the occurrence of vocal signatures in territorial songs of 27 male S. bilineata from 12 different-sized colonies in Panama. Males produced significantly more territorial songs when they had more territorial neighbors or when they had females roosting in their territories, indicating that male vocal activity rises with increasing male–male competition. Territorial songs are multisyllabic vocalizations with low-frequency buzz syllables being most prominent. We found statistical evidence for a pronounced individual signature encoded in the buzz syllables of territorial songs that could facilitate individual recognition among rival neighbors. Additionally, we found a vocal group signature in territorial songs, suggesting that young males may learn territorial songs from more than one tutor male. Resident male S. bilineata appear to cooperatively defend their colony against male intruders, making a group signature in territorial songs potentially advantageous.     

Experimental evidence that bright coloration is not important for territory defense in purple martins

Summary I tested the hypothesis that bright breeding plumage in territorial males acts as a badge of fighting ability or aggressive motivation to intimidate intruders. Territorial male purple martins (Progne subis) whose iridescent blue plumage was lightened to mimic the appearance of subadult males did not suffer an increase in intruder pressure or loss of territory compared with control males. Bright plumage color itself did not deter intruders and was not important for successful territory defense. Furthermore, a bright coloration of owners was not associated with an increased level of aggression toward intruders. Results from parallel studies on this species suggest that bright coloration is important in territory acquisition. The effectiveness of badges of fighting ability and aggressive motivation in territory defense is limited by whether intruders benefit from assessing these traits in owners. Differences in signaling systems between species are due in part to differences in floater tactics and the mode of territory acquisition.     

Acoustically mediated neighbor recognition in the North American bullfrog,Rana catesbeiana

Summary Playback experiments were conducted to determine whether territorial male bullfrogs (Rana catesbeiana) were capable of discriminating between advertisement calls of neighbors and strangers. Territorial males adjacent to subject males were removed and replaced with a speaker which broadcast calls of a stranger or the removed male. Ten of 11 males responded more strongly to calls of strangers than to calls of neighbors. When advertisement calls of neighbors were broadcast to subject males from positions within the removed neighbor's territory and from positions opposite the subject male, all 9 males tested responded more strongly to calls of a neighbor broadcast from a new position than to playbacks of the same call broadcast within the removed neighbor's territory. Because male bullfrogs recognize familiar calls and associate these calls with a particular direction or location, these data provide the first evidence for acoustically mediated neighbor recognition in frogs.     

Mating strategies of a nocturnal,desert rodent (Dipodomys spectabilis)

Summary The mating system of a nocturnal, desert rodent, the banner-tailed kangaroo rat (Dipodomys spectabilis) was studied through direct observation, live-trapping, and radiotelemetry over a 13-month period from August 1986 to August 1987. Mating behavior varied from exclusive matings between male and female neighbors to competitive mate searching and direct male competition. In summer matings and early in a November to May breeding season, males located receptive females and mated exclusively with them without disturbance from other males. As the operational sex ratio changed in favor of males, multiple males converged on an estrous female's territory and competed for access to her. However, an older, experienced male usually monopolized the matings of the same one to two close female neighbors for the entire breeding period, and females mated with the same male neighbor over several estrous cycles. Monopolization of females by neighbor males was facilitated by female relaxation of individual territorial defense. Dominant males spent considerable time in the territories of the females they monopolized before and during mating. This relaxation in territorial defense was seen in dyadic encounters in which females tolerated all males but allowed significantly more contact by neighbor than stranger males. Neighbor recognition, therefore, seems important in coordinating the mating interactions of this solitary rodent.     

Male Iberian rock lizards may reduce the costs of fighting by scent matching of the resource holders

Animals should adopt strategies to minimize the costs of intraspecific aggressive interactions. For example, individuals should be able to identify resource holders in advance and avoid fighting with them because residents are generally more likely than intruders escalate aggression. It has been suggested that scent marks function mainly to allow competitor assessment by conveying the costs of entering a scent-marked area. Individuals may identify territory owners by comparing the scent of substrate marks with the scent of any conspecific they encounter nearby, assessing whether these two scents match or not, a mechanism known as scent matching. Here, we examined the response of male Iberolacerta cyreni lizards to areas scent-marked by other males and the potential role of scent matching in agonistic interactions. We designed a laboratory experiment where we allowed a male to explore the scent-marked substrate of another male, and then we immediately staged agonistic encounters in a nearby clean neutral area with either the male that had produced the scent marks (matching treatment) or with a different non-matching individual male. The higher chemosensory exploratory rates of substrate scent marks in comparison to clean substrates suggested that males detected and spent more time exploring scent marks to obtain information on the donor male. Moreover, this information was later used to decide the fighting strategy. Intruding males delayed time until the first agonistic interaction, reduced the intensity of fights and the number of aggressive interactions, and won less interactions with males which scent matched that of scent marks (because they would be considered as the territory owners) than with other non-matching individuals. Our results show that male I. cyreni lizards use scent matching as a mechanism to assess the ownership status of other males, which could contribute to modulate intrasexual aggression, reducing costs of agonistic interactions.     

Exploitative compensation by subordinate age-sex classes of migrant rufous hummingbirds

Summary The three age-sex classes of rufous hummingbirds (Selasphorus rufus) that directly interact on southward migratory stopovers in our California study system differ in territorial ability and resource use. Immature males are behaviorally dominant to adult and immature females and defend the richest territories. Here, we test the hypothesis that the territorially subordinate age-sex classes compensate exploitatively for their exclusion from rich resources. Our results show that females were able to accumulate energy stores at rates comparable to males despite their subordinate territorial status. Territorial females gained body mass at the same rate and in the same pattern as males, and resumed migration at the same body masses. Moreover, during periods when birds were nonterritorial and used dispersed resources, adult and immature females maintained or gained body mass, whereas immature males lost mass. We suggest that females may be energetically compensated by (1) lower costs of flight incurred during foraging and defense, resulting from their lower wing disc loading, and (2) greater success at robbing nectar from rich male territories, resulting from duller coloration (immature females), experience (adult females), and, possibly, hormonal differences. In the future, experiments will be necessary to distinguish the various hypotheses about the mechanisms involved in compensation. Correspondence to: F.L. Carpenter     

The reproductive behavior of Anthidium manicatum (Hymenoptera: Megachilidae) and the significance of size for territorial males

Summary Males of the wool-carder bee, Anthidium manicatum, patrol clumps of garden plants. Females of this species visit these plants for pollen, nectar, and pubescence; they also mate there. Females are polyandrous, with intervals between copulations as short as 35 s. Patrolling males defend their territories (0.1–1.3 m²) against other males and against other species of flower-visiting insects. Honey bees may be rendered unable to fly by the attacks of A. manicatum.Territory owners perform exploratory flights to other males' territories, changing territories often (median ownership 4–7 days; maximum 30 days) and flying up to 450 m to establish new territories. Territorial usurpations are nearly always by larger males.Female visitation rate is significantly correlated with number of flowers on a territory. The head size of territory-owner males shows significant correlation with territorial quality (measured by number of flowers, not area) and thus with number of female visits and copulatory opportunities. Some males fail to maintain territories and instead attempt to forage and copulate in other males' territories while the owners are otherwise occupied. Nonowner males are significantly smaller than owners, forage less often and from fewer flowers, and achieve significantly fewer copulations than owners. Females, however, do not reject smaller, nonowner males at a higher rate than they do larger, owner males; their choice for male size appears to be indirect, based instead on choice of food resource.The interval between a copulation and the male's next attempt with a different female is not shorter than that involving the same female. Males do not escort just-mated females about their teritories, as observed in Anthidium maculosum. Territorial behavior in this species most likely evolved through intrasexual competition for reproductive success which led to sexual dimorphism. The defense of a resourcebased territory is the mechanism used by a male to maximize his reproductive potential.     

Costs and benefits of territorial defense in wild golden lion tamarins,Leontopithecus rosalia

Summary The costs and benefits of territorial defense were examined in a group of five wild golden lion tamarins, Leontopithecus rosalia, at Poco d'Antas Biological reserve, Rio de Janeiro, Brazil. I examined the effects of both interference and exploitative competition between groups of tamarins by comparing their use of space, time budgets and foraging success in different contexts of intergroup interactions and in quadrats shared and not shared by other groups. Tamarins spent more time moving and vocalizing, and less time feeding, foraging, and resting during intergroup encounters than in non-encounter contexts. Irrespective of intergroup distance, the group spent more time in overlapping areas of the range periphery than expected on the basis of quadrat availability. In those areas, however, foraging success per unit of foraging effort was lower than in exclusive areas of the range center. This suggests that access to high payoff central areas depended on costly defense (by both interference and exploitation) of the range periphery. Time and energy invested by the resident group in territorial defense (1) increased the availability of food in the range center, and (2) minimized food loss to neighboring groups in the range periphery. These benefits are likely to justify the costs of defense for an animal which depends on easily-depletable food supplies, such as prey in microhabitats and small concentrations of fruits and nectar.     

An experimental study of male adornment in the scarlet-tufted malachite sunbird: II. The role of the elongated tail in mate choice and experimental evidence for a handicap

Summary Scarlet-tufted malachite sunbirds (Neetarinia johnstoni) are endemic to the high altitude zones of East African mountains. On Mount Kenya the males are resident and territorial all year. The females arrive over an extended period at the beginning of the breeding season, after spending the non-breeding season in nomadic flocks at slightly lower elevations. Males are bright iridescent green with elongated central tail feathers, which are displayed during courtship. We examined the role of the tail in mate choice using natural variation and investigated the influence of tail length on male time budgets by experimental manipulation. Territorial males that paired had longer tails than territorial males which remained unpaired. Males with naturally long tails started breeding earlier, resulting in fledglings being produced earlier in the season when the weather was more clement. Birds which bred together in one year were paired together in the next year if they both survived. Thus the male's tail may only be involved as a cue in the formation of new pairs. Males which were already paired were subjected to one of three experimental treatments — having their tail elongated, shortened, or manipulated but kept at the same length. Males with experimentally shortened tails spent more time in flight and hawked for flying insects with a higher efficiency than control males. Both control and elongated tail males reduced the amount of time in flight and had a lower hawking efficiency after manipulation. These results suggest that the long tail of male scarlet-tufted malachite sunbirds is a handicap. The factors influencing the reproductive success of a pair are discussed. Offprint requests to: M.R. Evans     

Resource-holding power asymmetries,the prior residence effect,and reproductive payoffs in male northern elephant seal fights

The effect of resource-holding power (RHP) and prior residency asymmetries on fight outcome and subsequent seasonal copulatory success was analyzed for fights between marked male northern elephant seals (Mirounga angustirostris). RHP asymmetries were measured as differences in estimated mass and prior residency asymmetries were measured as differences in beach tenure prior to the fight. The principal results were: (a) Neither differences in mass nor differences in beach tenure had any effect on fight outcome as separate factors. (b) Mass and tenure differences had an interactive effect on fight outcome; fight winners were either heavier males present for shorter periods (intruders) or lighter males present for longer periods (prior residents). (c) Winners of fights copulated more often than losers after a fight throughout the breeding season; this difference was smallest for low-ranking males, larger for high-ranking males in short fights, and greatest for high-ranking males in long fights. (d) Prior resident males who won long fights obtained significantly more copulations after a fight than the males they defeated, but this was not true for intruder males who won long fights. These results suggest that male northern elephant seals will incur greater contest costs (i.e., fight for longer periods and/or against heavier males) for higher reproductive payoffs. They also imply that, at least for males in long fights, differences in prior residence represent payoff asymmetries, with higher reproductive payoffs for winning prior residents than for winning intruders.     

Risks and benefits of lethal male fighting in the colonial,polygynous thrips Hoplothrips karnyi (Insecta: Thysanoptera)

Summary Males of Hoplothrips karnyi (Hood) (Insecta: Thysanoptera), a colonial fungus-feeding thrips, fight each other in defense of communal egg mass sites, where they mate with females that come to oviposit. Fighting males stab each other with their enlarged, armed forelegs and hit each other with their abdomens. Escalated fights occur between large males of similar size. Fights are often lethal; males that died during observations fought more frequently than other males, were stabbed more often and more severely than other males, and were relatively large, but somewhat smaller than their opponents. Large males tend to win fights and guard egg masses, and they secure about 80% of last matings before ovipositions. Guarding males apparently assess female reproductive condition by putting their forelegs partially around females' abdomens; guarding males, but not nonguarding males, mate preferentially with females that have yet to oviposit. Non-guarding males mate with females away from egg masses, sneak matings at egg masses, and occasionally challenge guarding males. Challenges tend to follow matings by non-guarding males at egg masses. Each of four observed or inferred takeovers was followed by the death of the guarding male that lost. Male fighting strategies are discussed in terms of the consistency of lethal fighting with game theory models. Guardin males appear to pursue a classical hawk strategy of escalate until injured or victorious. This strategy may be advantageous because only large males become guarders, the mating success of guarders greatly exceeds that of non-guarders, and high population viscosity ensures that benefits from killing an opponent accrue directly to gaurders. The occurrence of challenges by large non-guarders implies that fighting ability and resource value asymmetries between males change over time; such changes may result from the energetic costs of guarding, injury to guarding males, or depletion of guarding males' supply of sperm.     

Territorial defence in the great tit (Parus major): Do residents always win?

Summary I removed resident pairs of great tits from their territories for short periods and released them after replacement pairs had occupied the spaces. When two pairs are manipulated in this way into occupying the same territory an escalated contest ensures. Contests between residents and replacements are longer, more likely to involve physical fights and longer fights or displays than contests between established neighbours or residents and intruders. The degree of escalation between residents and replacements is an increasing function of replacement time. It rises to a peak and then diminishes again. The probability that the replacement will defeat the former resident is an increasing function of replacement time, reaching 90% after several days. These results are consistent with the hypothesis that territorial residents win in contests against intruders because of an asymmetry in payoff rather than an asymmetry in resource holding potential or an arbitary convention. A possibly asymmetry in payoff in the great tit is the cost of defending the territory against neighbours. The cost is higher for replacements than for residents.     

The effect of prey consumption on territorial defense by harriers: differential responses to neighbors versus floaters

Summary Food consumption may reduce fighting intensity of territory owners by decreasing resource value (additional food cannot be consumed) and/or increasing fighting costs (food in the digestive tract may raise injury risks). A territorial harrier's (Circus cyaneus, adult females) decision to reduce its level of aggression should depend upon whether or not the intruder was a competitor for individual prey items (as are smaller male floaters) or for the territory proper (as are female floaters and especially female neighbors). Accordingly, following meals, aggressive intensity of owners was strongly reduced towards male floaters (more were ignored), slightly reduced towards female floaters (more were called at than chased), and remained unchanged towards neighbors (virtually all were chased). Hence, alterations in aggressive behavior of territory owners following food consumption may depend upon the type of intruder and the resource under contest (a food item or a territory).     

Adaptation,compromise, and constraint: the development,morphometrics, and behavioral basis of a fighter-flier polymorphism in male Hoplothrips karnyi (Insecta: Thysanoptera)

Summary Males of the colonial, wing-polymorphic thrips Hoplothrips karnyi (Hood) fight each other with their forelegs in defense of communal female oviposition areas. In this study, males were reared individually under varying conditions of food deprivation to investigate the developmental cues used in morph determination and the relationships between wing morph, developmental time in each instar, propupal weight, and five adult morphological characters associated with fighting ability and dispersal ability. Males deprived of food for five days midway through the second (final) larval instar had smaller propupal weights and were more likely to develop wings than males deprived of food in the first instar or control males. However, the mean propupal weight of all males that developed wings was not significantly less than that of wingless males. Wing morph of female parents had no measurable effect on this character in the offspring. Wingless males possess relatively larger fore-femora and prothoraces than do winged males, but winged males possess relatively larger pterothoraces (Fig. 1). Behavioral observations of wingless and winged males of similar weight as propupae showed that wingless males won fights and became dominant in oviposition areas. Thus, a trade-off exists between characters associated with male fighting and dispersal ability. The cost of wings, in terms of fore-femora size and prothorax size, increased with propupal weight. Wingless males that developed in the experimental treatment that produced a high proportion of winged males were relatively small in size, and were intermediate in body shape with respect to winged males and other wingless males (Fig. 2). This shape intermediacy indicates that there may be developmental constraints on alternative tactics of resource allocation. Total developmental time varied between wing morphs, but was not correlated with propupal weight or adult morphological characters of winged or wingless males. For wingless males that developed in the treatment that produced a high proportion of winged males, adult morphological characters were negatively correlated with the duration of the second instar. This correlation suggests that the development of small wingless males involves a compromise between the benefits of large adult size and the costs of prolonging the second instar to increase the probability of becoming larger.     

Alternative mating tactics in males of Polistes dominulus (Hymenoptera: Vespidae)

Summary In summer, males of Polistes dominulus form large aggregations at sunny landmarks. We identified two size-correlated behavioural categories: residents (R) and transient (T). R males, which constitute 20%–25% of the total population, are larger than T males, territorial, aggressive, and more site-faithful, while T males range more widely, are non-aggressive, and show little site tenacity. Field and laboratory data suggest that R males have an advantage in mating, particularly if they engage in frequent flights while on their territories. These alternative mating tactics within the same population are combined with behavioural flexibility in some individuals, which switch from one option to the other.     

Defending young biparentally: female risk-taking with and without a male in the burying beetle, <Emphasis Type="Italic">Nicrophorus pustulatus</Emphasis>

A positive correlation between the parental effort of a male and female should promote stable biparental care. Risk-taking (as assessed by injuries) against infanticidal intruders by Nicrophorus pustulatus females was expected to be low when females had a low probability of successful defense of the young. I tested the hypothesis that when the presence of a male partner increased the probability of successful defense from low to moderate that female risk-taking would increase. Single females and pairs with first instar larvae were confronted by potentially infanticidal male and female conspecific intruders. Male intruders routinely took over nests from unpaired females (30 of 36 trials). Unpaired females and male intruders were injured infrequently, indicating less intense fights despite the high probability of infanticide. A resident female defending against a male intruder was injured more often when paired than unpaired, suggesting greater risk-taking. A male parent that delays desertion, therefore, receives fitness benefits not only from his own defense of the young, but from greater female defense against male intruders as well. It is hypothesized that the threat of infanticidal takeovers by males promotes extended biparental care in burying beetles. When the intruder was female, on the other hand, a female parent on her own had a moderate probability of successfully defending the brood (22 of 36 trials). The presence of a male partner against female intruders almost guaranteed successful defense (35 of 36 trials) and female intruders did not appear to contest pairs vigorously. Against female intruders the presence of a male partner did not significantly change injury rates of the defending female.     

Do male tree swallows guard their mates?

Summary We monitored the time spent at the nest and following behavior of mated tree swallows to determine if males were guarding their mates. The proportion of time spent together at the nest did not decrease significantly between fertile and postfertile periods, and the tendency of males to follow females was not significantly different from that of females to follow males. Following by either sex was infrequent. We suggest that the lack of mate guarding in tree swallows is related to an apparently low probability of extra-pair copulations, which in turn is likely to be due to two factors. Nesting opportunities are limited, perhaps more so for females than males. If the operational sex ratio is skewed towards females, this would not only reduce the risk of extra-pair copulations, but would also select against promiscuous females which would risk being abandoned by their mates. Secondly, under natural conditions, the limited availability of nest sites has selected for territorial defense by both males and females, which may decrease the occurrence of extra-pair copulation. Both factors would lead to relaxed selection for mate guarding behavior.     

Tit for tat among neighboring hooded warblers

Summary The dear-enemy relationship of territorial songbirds could be mutually beneficial to neighbors, as males who recognize neighbors and reduce their responses to these neighbors would require less time and energy for territorial defense. In order for this relationship to be evolutionarily stable, this reduction in response to a neighbor must be conditional on reciprocal restraint by that neighbor. This study examined the possibility of such conditional responses in hooded warblers (Wilsonia citrina). Responses of territorial hooded warblers to playbacks of neighbors' songs from shared boundaries were measured before and after playbacks that simulated intrusions of those same neighbors (NNNN treatment) or strange birds (NSSN treatment) into the subjects' territories. Each male received both treatments separated by at least 8 days. Males increased their responses to playbacks of a neighbor's songs at the boundary after simulated intrusions of that same neighbor (NNNN) but did not increase their responses to such playbacks after simulated intrusions of strangers (NSSN). This increased response to a defecting neighbor suggests that the relationship between neighboring territorial hooded warblers is based on a conditional strategy like tit-for-tat.     

Sex change limited by paternal care: a test using four Mediterranean labrid fishes,genus Symphodus

Four species of the Mediterrnean wrasse (genus Symphodus) were investigated under natural conditions near Calvi, Corsica, France, to test the idea that extensive male mating-investment limits the extremes of male reproductive success, and thus reduces selection for protogynous sex change. The four species differ in the extent to which males build nests and care for the eggs, and this sort of paternal care can detract from time spent in mating. In S. ocellatus and S. roissali larger males construct an elaborate nest, ventilate the eggs, and engage in territorial defense. The spawning rates for these males are relatively low and variable due to long periods spent in nest construction and egg tending. They also suffer a large amount of interference from smaller males, which may be due to the predictability of nest location. Sex change appears to be absent. S. tinca males construct only a rudimentary nest, do not ventilate the eggs, and experience much less spawning interference. Large males are relatively more successful in mating in this species, and sex change appears to occasionally occur. The large males of S. melanocercus spawn at a much higher rate than small males, due in part to the fact that they do not construct or defend nests and thus are able to spawn on a daily basis. Sex change appears to be common in this species. Thus, the species that shows the greatest sexual difference in changes of expected fertility with size is also the species that shows the strongest expression of sex change. Studies such as this can begin to indicate the actual costs of changing sex.     

A test of the "dear enemy effect" in the strawberry dart-poison frog (<Emphasis Type="Italic">Dendrobates pumilio</Emphasis>)

Some territorial animals exhibit a form of social recognition, commonly termed the "dear enemy effect", in which territory residents display lower levels of aggression toward familiar neighbors compared to unfamiliar individuals who are non-territorial "floaters". Despite the widespread occurrence of territorial social systems and use of acoustic signals for communication in anuran amphibians, only two previous studies have demonstrated vocally mediated dear enemy behavior in a territorial frog. In this study, I conducted neighbor-stranger discrimination playback experiments in a third species of territorial frog, the strawberry dart-poison frog, Dendrobates pumilio (Anura, Dendrobatidae). In the first experiment (n=24), I broadcast the calls of a subject's nearest neighbor and the calls of an unfamiliar individual from the approximate midpoint between the subject's and the neighbor's territories. Although males responded to the stimuli, they did not exhibit differential responses to the calls of neighbors and strangers. In a second experiment (n=22), I broadcast the calls of a neighbor and a stranger to subjects through a speaker located in the approximate center of the neighbor's territory. Males also responded to the playback, although less intensely than in the first experiment, but no discrimination between the calls of neighbors and strangers was found. Thus, territorial males of the strawberry dart-poison frog appear not to discriminate behaviorally between the advertisement calls of neighbors and strangers. Several proximate and ultimate-level hypotheses for this lack of vocally mediated neighbor-stranger discrimination are discussed.Communicated by T. Czeschlik