Territorial Encounters Research Articles

Vocal duets in a nonpasserine: an examination of territory defence and neighbour–stranger discrimination in a neighbourhood of barred owls

Mated pairs of animals in many taxa coordinate their vocalizations into duets, yet most research on duetting has focused on songbirds. Here we examine the duetting behaviour of barred owls (Strix varia) by addressing three questions: (1) Do owl duets play a role in territorial interactions? (2) Do owls discriminate between duets of neighbours versus strangers? (3) Do duets play a role in extended communication among a neighbourhood of owls? We simulated territorial encounters by broadcasting duets of adjacent, territory-holding owls (neighbours) and distant owls (strangers). We assessed responses to playback using a 3.5-km transect of automated recording devices. We compared vocal activity during a pre-playback period and following both playback treatments for the focal pair, their neighbours, and more distant owls within the neighbourhood. After playback, focal owls gave significantly more duets, vocalized for a longer duration, and emphasized different call types compared to the pre-playback period, demonstrating that barred owls use duets in territory defence. Focal owls did not respond significantly differently to neighbours versus strangers. At the neighbourhood level, owls did not behave differently during silent pre-playback periods or post-playback periods. Our results suggest barred owl duets function primarily in immediate confrontations during territorial conflicts.

Transgressive aggression in Sceloporus hybrids confers fitness through advantages in male agonistic encounters

1. We investigated agonistic behaviour and associated characteristics of Sceloporus woodi (Florida scrub lizard), Sceloporus undulatus (Eastern fence lizard) and their hybrids using staged territorial encounters. 2. These Sceloporus hybrids exhibit transgressive aggression and transgressive head-girth relative to the parental species and the transgressive aggression was specifically associated with an advantage in agonistic encounters. Our results suggest a hybrid advantage in natural habitats when defending and invading territories against either parental species. 3. We further analysed general advantages in agonistic encounters across the entire three-group system to elucidate characteristics that may be advantageous under specific circumstances. Individuals with larger body size (SVL) and greater aggression had an overall advantage in agonistic encounters; however, smaller individuals could win when slightly more aggressive and fatter, and less aggressive individuals could win when slightly larger, especially with greater head-girth. 4. The extreme hybrid phenotypes likely occurred through transgressive segregation, which has been implicated as a process through which homoploid, hybrid speciation can occur. Some form of ecological divergence is necessary, however, to impede parental gene flow. Our data suggest that ecological divergence could manifest in territorial species through transgressive aggression.

Four type of sounds for one winner: vocalizations during territorial behavior in the red-mouthed goby Gobius cruentatus (Pisces Gobiidae)

During territorial encounters, the acoustic repertoire of Gobius cruentatus consists of four types of sound emissions: a tonal sound, a noisy tonal sound, a train of individual pulses, and a complex sound. The complex sound is made of two distinct elements, an initial tonal part followed by pulses. This is the largest acoustic repertoire described so far in gobiid fish during aggressive interaction. Sounds are emitted, mainly by the residents, when fish have already started the interaction but before the encounter is settled. Therefore, sounds seem to have a threatening function.

Does Sex Trade with Violence among Genotypes in Drosophila melanogaster?

The evolutionary forces shaping the ability to win competitive interactions, such as aggressive encounters, are still poorly understood. Given a fitness advantage for competitive success, variance in aggressive and sexual display traits should be depleted, but a great deal of variation in these traits is consistently found. While life history tradeoffs have been commonly cited as a mechanism for the maintenance of variation, the variability of competing strategies of conspecifics may mean there is no single optimum strategy. We measured the genetically determined outcomes of aggressive interactions, and the resulting effects on mating success, in a panel of diverse inbred lines representing both natural variation and artificially selected genotypes. Males of one genotype which consistently lost territorial encounters with other genotypes were nonetheless successful against males that were artificially selected for supernormal aggression and dominated all other lines. Intransitive patterns of territorial success could maintain variation in aggressive strategies if there is a preference for territorial males. Territorial success was not always associated with male mating success however and females preferred ‘winners’ among some male genotypes, and ‘losers’ among other male genotypes. This suggests that studying behaviour from the perspective of population means may provide limited evolutionary and genetic insight. Overall patterns of competitive success among males and mating transactions between the sexes are consistent with mechanisms proposed for the maintenance of genetic variation due to nonlinear outcomes of competitive interactions.

The structure, context and functions of group singing in black-breasted wood-quail (Odontophorus leucolaemus)

Black-breasted wood-quail (Odontophorus leucolaemus) are vocal, group living birds (covey size ranges from 2 to 15 individuals) that inhabit the dense understory of highland forest in Costa Rica. Mated pairs produce coordinated duets and groups produce coordinated choruses that are audible to humans from a distance of at least 200 m. Duets and choruses are antiphonal; they consist of two syllables that are comprised of two elements each, which are repeated over and over in an alternating fashion. Neighbouring coveys are most often heard calling back and forth just after dawn and all group members participate in singing and territory defence. During territorial encounters, group singing is often accompanied by displays, chases, and even physical fights between members of opposing coveys. Black-breasted wood-quail produce at least five structurally distinct close-range calls that are associated with within-group communication and territorial encounters. Observations of the context of unprovoked duets and choruses, in addition to responses to simulated territorial intrusion using playback, indicate that these songs play an important role in territory advertisement and defence. Furthermore, black-breasted wood-quail may adjust their response to playback as a function of relative group size, suggesting that choruses could function in relative numerical assessment of group size.

Behavioral and neuroendocrine consequences of social subjugation across adolescence and adulthood

BackgroundSocial subjugation is a very significant and natural stressor in the animal kingdom. Adult animals defeated and subjugated during establishment of dominance hierarchies or territorial encounters can be highly submissive in future agonistic interactions. While much is know about the biological and behavioral consequences of winning and losing fights in adulthood, little is known about adolescence; a developmental period noted for impulsivity and heightened agonistic behavior. The present studies were undertaken to determine if the behavioral and neuroendocrine consequences of social subjugation are comparable in adolescent versus adult Syrian golden hamsters (Mesocricetus auratus). Male siblings were studied from adolescence into adulthood following exposure to counterbalanced episodes of either a benign stressor, i.e., isolation in a novel cage, or the more severe stressor of social subjugation.ResultsAs adults, hamsters with a history of social subjugation in adolescence show high levels of aggression toward intruders as compared to siblings subjugated in adulthood. Sibling controls subjugated in adulthood are highly submissive with little or no aggressive behavior. However, when subjugated in adulthood, hamsters with the earlier history of subjugation are no different than their sibling controls, i.e., adult subjugation promotes submissive behavior. Sexual motivation is high in adult hamsters with adolescent subjugation and testosterone levels remained stable over adulthood. In contrast, sibling controls subjugated in adulthood show lower levels of sexual motivation and reduced levels of testosterone. Release of cortisol during agonistic encounters is blunted in animals subjugated in adolescence but not adulthood. Measures of anxiety are reduced in hamsters with adolescent subjugation as compared to their sibling controls.ConclusionThese data demonstrate a pronounced difference in behavior and neuroendocrinology between adolescent and adult hamsters in their response to social subjugation and suggest adolescence is a resilient period in development.

Duet song and sex roles during territory defence in a tropical bird, the black-bellied wren, Thryothorus fasciatoventris

A diverse array of bird species show a behaviour known as duet singing, in which mated pairs sing temporally coordinated songs. Several studies have shown that simulating territory intrusion with conspecific song playback evokes duet song from duetting bird species, but the adaptive significance of coordinated song during territorial defence remains unclear. The function of duetting is further obscured by our poor understanding of the roles of the sexes in territory defence among year-round territorial species. We developed a simple optimality model that predicts the conditions under which intersexual territorial defence is most likely to occur. We used male solo song and female solo song playback as well as a novel method called ‘stereo duet playback’ to test the predictions of the model and to explore the function of song initiation and song answering during territorial encounters. We conducted these experiments in the field on the black-bellied wren, a year-round territorial passerine. Birds of both sexes responded to all treatment types. Males initiated more songs during opposite-sex playback than during same-sex playback and both sexes were more likely to answer their mates' songs when mates were physically closer. We argue that the acoustic mate-guarding hypothesis does not adequately account for these results, and suggest that duetting during territorial encounters allows mates to identify one another, thus preventing intrapair aggression. As predicted by our model, females showed a strong same-sex bias in territory defence, whereas males approached playback of both sexes. Also in support of the model, males with dependent juveniles showed stronger intersexual territoriality than males not involved in a breeding effort.

Functions of duetting in the tropical boubou, Laniarius aethiopicus: territorial defence and mutual mate guarding

Duetting, found in many animal taxa, is still a poorly understood form of signalling behaviour despite numerous hypotheses to explain its function. One contentious issue is whether duetting is a cooperative endeavour or signals conflict between the sexes. We studied the function of duetting in the tropical boubou, using interactive playback experiments. We staged encounters by presenting paired birds with four variants of each of four duet types (neighbour and stranger solos and neighbour and stranger duets). Multiple lines of evidence suggest that both joint territorial defence and mutual mate guarding are important functions of duetting, and that both cooperation and conflict between males and females have shaped duetting behaviour. Of a repertoire of 12 duet types, eight were used for joint territorial defence. Two of these eight duet types were probably also used for mutual mate guarding, suggesting that individual duets can have multiple functions. We found an unusual response for duetting birds in that females often synchronized notes with male solo playback to form precise duets. In turn, males attempted to jam the song of rivals when females joined the song of male solo playback, providing further evidence for the importance of acoustic mate guarding. Song jamming by males has not previously been described for duetting species. Finally, we suggest that the repertoire of duet types is used to fine-tune territorial encounters in a network environment of multiple interactants.

Territoriality and Neighbor Assessment in Brown Jays (Cyanocorax Morio) in Costa Rica

AbstractDefense of group-held resources is a common and widely accepted function of territorial interactions between neighboring groups. In addition, territorial interactions could provide opportunities to assess members of neighboring groups and reproductive opportunities there, or to solidify status in the home group. We studied group-level characteristics and individual participation in territorial encounters in the cooperatively breeding Brown Jay (Cyanocorax morio). Intergroup encounters at stable territory boundaries include both aggressive and affiliative behavior, which suggests that a territorial encounter could function as both a resource defense mechanism and as an arena for social interactions. Territory characteristics that increase the probability of contact between groups (long boundaries, large combined group size, and home range overlap) explain much of the variation in frequency of territorial encounters. Male-biased dispersal was more common to neighboring groups with long boundaries, supporting the idea that frequent interactions between neighbors facilitate dispersal. Females usually inherit breeding positions on their natal territories, and participation in intergroup encounters by females does not vary with age or breeding status. In addition to defending group resources, females on their natal territories could be defending their positions in the breeding queue. Immigrant females are not likely to breed successfully, or to disperse again, and they participated less than expected. Participation by both natal and immigrant males varied by age; young males, at the ages when dispersal and intergroup forays are most likely, participated more than expected, whereas older males (≥4 years) participated less. That is consistent with the hypothesis that participation in intergroup encounters facilitates dispersal and improves integration into social groups. Because extragroup matings occur in this population, both breeding females and males could be assessing neighboring individuals for mating opportunities. Resource defense and social facilitation are not mutually exclusive hypotheses, and our observations suggest that both are important components of territorial encounters in Brown Jays.

TERRITORIALITY AND NEIGHBOR ASSESSMENT IN BROWN JAYS (CYANOCORAX MORIO) IN COSTA RICA

Abstract Defense of group-held resources is a common and widely accepted function of territorial interactions between neighboring groups. In addition, territorial interactions could provide opportunities to assess members of neighboring groups and reproductive opportunities there, or to solidify status in the home group. We studied group-level characteristics and individual participation in territorial encounters in the cooperatively breeding Brown Jay (Cyanocorax morio). Intergroup encounters at stable territory boundaries include both aggressive and affiliative behavior, which suggests that a territorial encounter could function as both a resource defense mechanism and as an arena for social interactions. Territory characteristics that increase the probability of contact between groups (long boundaries, large combined group size, and home range overlap) explain much of the variation in frequency of territorial encounters. Male-biased dispersal was more common to neighboring groups with long boundaries, ...

Modes of cooperation during territorial defense by African lions.

Cooperation during territorial defense allows social groups of African lions to defend access to resources necessary for individual reproductive success. Some forms of cooperation will be dependent upon cognition: reciprocity places greater cognitive demands on participants than does kinship or mutualism. Lions have well-developed cognitive abilities that enable individuals to recognize and interact with others in ways that seem to enhance their inclusive fitness. Male lions appear to cooperate unconditionally, consistently responding to roaring intruders regardless of their male companions' kinship or behavior. Female lions, however, do keep track of the past behavior of their female companions, apparently using the reliability of a companion as one means of assessing the risks posed by approaching intruders. Some "laggard" females may exploit the cooperative tendencies of "leaders" during territorial encounters. Although leader females clearly recognize laggards as such, the costs of tolerating laggards may be less than the benefits leaders gain through territorial defense behavior. Thus, although lions clearly have the cognitive ability to base cooperation on reciprocity, territorial defense cooperation appears instead to be based primarily on mutual benefits to participants for both male and female lions.

Prior residence, body size and the dynamics of territorial disputes between male freshwater angelfish

Territorial interactions between pairs of size mismatched, sexually mature male angelfish Pterophyllum scalare were investigated in three different conditions: with the larger fish resident (the large resident condition), with the smaller fish resident (the small resident condition) and in a neutral territory (the neutral condition). In the two resident conditions, approximately half of the intruders had previously held territories and half had not. In all categories of fight, one fish showed submissive postures and lost the fight; eventual losers performed both attack and threat at a lower rate than eventual winners. Attack rate declined as the encounter progressed, while rate of performance of threat postures increased. In fights on neutral territories, the larger fish won all fights. In all fights with a resident‐intruder asymmetry, the resident fish won the encounter, regardless of relative size. In eventual winners but not in eventual losers, levels of attack were lowest in the neutral encounters. In the small resident condition, levels of attack (corrected for activity of the resident) were lower in intruders that had previously held a breeding territory. Relative size influenced behaviour shown during fights, in that overall intensity was correlated negatively with size differential in all conditions. Thus although prior residence is the primary determinant of the outcome of territorial encounters in this species, both relative body size and prior possession of territory also influence the nature of the interaction.

Does darkening signal submission in territorial contests between juvenile Atlantic salmon, Salmo salar ?

Communication by means of visual signals occurs during the competitive, aggressive and sexual interactions of many animals. Some animals such as fish are able to change their body coloration rapidly, and there is evidence that this is used as a means of signalling. However, the precise meaning of such signals is rarely understood. We examined whether (1) darkness in juvenile Atlantic salmon is associated with submission, and (2) changing to a darker colour could act as a signal to the opponent and hence induce a change in its behaviour. We found that both the sclera of the eye and the overall body coloration tended to darken in fish that were losing territorial encounters, while victors retained their original coloration. The darkening was rapid and usually occurred during a period of sustained attacks by the opponent; however, the aggression level decreased as soon as the losing fish had become darker. We suggest that the darkening of the losing fish was associated with submission and may result in a change in the behaviour of its opponent, so minimizing the potential risk of injury during unnecessarily prolonged fights.

Size assessment in simulated territorial encounters between male green frogs ( Rana clamitans )

We examined the ability of male green frogs to assess the size of an opponent based on the dominant frequency of their advertisement call, which is negatively correlated with size, using synthetic stimuli to simulate intruders of different sizes. In one field playback experiment, we broadcast a pair of stimuli representing a small and a large male; in a second experiment, we broadcast calls of a medium and a large male. In both experiments, males produced calls with significantly lower dominant frequencies in response to each stimulus. Contrast analyses revealed that males lowered the dominant frequency of their calls more in response to the large-male stimulus than in responses to the small- and medium-male stimuli. In the second experiment, males also responded to the large-male stimulus by calling at higher rates. There were no differences in mean note duration or the number of moves made toward or around the playback speaker in response to any stimulus. Thus, the frequency of an opponent's calls elicits a differential modification of calling behavior, primarily in the form of differential dominant frequency alteration, suggesting that males use dominant frequency to assess the size of opponents during aggressive encounters.

Song‐type function during territorial encounters in male Cetti's Warblers Cettia cetti

During undisturbed singing, male Cetti's Warblers Cettia cetti sing constantly the same song type (S‐song), which is stereotyped individually but differs between individuals. When facing a territorial dispute, males may start to sing a distinct song type (I‐song) used only in this context. To evaluate the functional significance of these two song types in the communication system of Cetti's Warbler, two series of playback experiments were performed. When exposed to repeated S‐songs of an extraneous male, most of the ten birds tested ceased to sing S‐songs and used I‐songs, generally while displaying aggressive reactions. After a while, they started to sing S‐songs again but at a higher rate than before the playback. In a second series of experiments, seven birds were first exposed to a playback of S‐songs and then to a second stimulation with three I‐songs or with three further S‐songs. The birds tended to approach the speakers in response to the first playback but, in most cases, withdrew from them after the second one. No significant differences in the reactions of the test birds were found between the trials using S‐songs and those with I‐songs. The present results indicate that the two song types constitute two signals associated with territorial behaviour; the song type emitted is probably dependent on the singer's level of aggressiveness.

Female-limited variability in mimicry in the swallowtail butterfly Papilio polyxenes Fabr.

Variation in dorsal and ventral aspects of mimetic wing patterns was measured in the sexually dimorphic swallowtail butterfly Papilio polyxenes, a Batesian mimic of Battus philenor. The pattern on the dorsal surface of the wings makes females better mimics than males and was more variable in females. The pattern on the ventral surface of the hind wings, which provides a similar degree of mimicry in both sexes, was equally variable in both sexes. Full-sib ANOVA indicated that variability in dorsal and ventral patterns was similarily heritable in both sexes, suggesting that the increased variability in females is not simply the result of suppressed expression of genetic variation in males. The results are consistent with the hypothesis that variation in two sets of modifier loci, only one of which is expressed in males, influences the dorsal pattern, resulting in greater variability in females. The nonmimetic dorsal pattern in males is probably maintained as a consequence of sexual selection arising from male-male competition in territorial encounters. The generality of the reduced male variability in the Lepidoptera is discussed.

Tail length affects territory ownership in the yellow-shouldered widowbird

Abstract. Bright and conspicuous colours and ornaments of male birds are often attributed to female choice, but alternative hypotheses, such as male-male competition for females or resources, are rarely considered. Yellow-shouldered widowbirds, Euplectes macrourus, are sexually dimorphic, polygynous birds in which males have long tails. Males with experimentally shortened tails were less likely to acquire or retain territories (4 of 11) than controls (7 of 9) or males with lengthened tails (9 of 10). This was not due to indirect effects of the experimental treatments on male behaviour, as the displays used in territorial encounters did not differ in their frequency among the treatment groups. Tail length did not appear to affect female choice, as there was no correlation between natural tail length and male attractiveness (measured as the number of females nesting in his territory) and no difference between treatments in the number of females nesting in a male's territory. Thus, male-male competition for territories can also lead to the evolution of ornaments and may be an important factor in the evolution of conspicuousness.

Territorial Significance of Scent Marking during the Non‐mating Season in the Aardwolf Proteles cristatus (Carnivora: Protelidae)

AbstractPatterns of scent‐marking by male and female aardwolves during the non‐mating season in the northern Cape Province are described. The distribution of scent marks conforms to predictions for marks being used as territorial advertisements. Scent marks were concentrated around territory borders and were deposited at increasingly higher densities in smaller territories. The data are used to re‐examine existing hypotheses as to how scent marks function in territory maintenance. Scent marks provide an olfactory association between the resident and the defended area, but I suggest that the message provided by this association may depend heavily on territory size, the frequency of territorial encounters and the defensive behaviour of the resident. The greater the territory size and hence the difficulty in monitoring intrusions, the greater the threat transmitted by scent marks needs to be. In most territorial carnivores, scent marks may be interpreted by intruders as a threat of immediate physical attack if encountered by the resident. Thus scent marks help to maintain, but cannot ensure, territorial integrity in the temporary absence of the resident.

Territoriality in a Terrestrial Salamander: the Influence of Resource Quality and Body Size

AbstractIntraspecific interference competition associated with territoriality has been documented in laboratory studies of the red-backed salamander, Plethodon cinereus. I used laboratory and field experiments to study the effect of resource quality and body size on such competition. In an experiment in southwestern Virginia, cover objects (e.g., logs) from which the resident salamanders were removed were invaded significantly more often than cover objects from which the resident salamander was not removed. These data provide the first direct test of territoriality for a salamander in a natural habitat. Newly invading salamanders were significantly smaller than the original territorial residents. Therefore, large body size is an advantage in territorial encounters. Because cover objects are important resources for terrestrial salamanders, characteristics of the cover object may contribute to territory quality. In an experiment conducted during warm summer weather at the Virginia site, soil temperatures under large cover objects were significantly cooler than those under small cover objects or under the leaf litter. Large cover objects may therefore benefit the salamanders by providing a buffer zone between the salamander and extreme environmental temperatures on the forest floor. In both laboratory and field experiments, when salamanders were offered a choice between large and small cover objects, both large and small salamanders exhibited a significant preference for large cover objects. Also I censused cover objects in a natural mixed hardwood forest habitat during courting and noncourting seasons and, for both seasons, I found a significant positive correlation between the body size of the salamander and the size of the cover object that it occupied. I conclude that, in this natural forest habitat, there is intraspecific competition for high quality cover objects and larger individuals are more successful competitors than smaller individuals.

Geographic variation in the territorial success ofDrosophila melanogaster males

Drosophila melanogaster males defend food against other males to increase their access to females on food. The territorial behavior of stocks collected from Townsville, Corindi, and Melbourne on the east coast of Australia were compared. Males from these stocks showed the same incidence of territorial encounters. However, Melbourne males were more successful at obtaining territories in competition with Townsville or Corindi males. This difference could be accounted for largely by variation in body weight, although territorial success was also determined by other factors because Townsville and Corindi males that held territories were not heavier than Melbourne males. In reciprocal crosses between the populations there was directional dominance for increased territorial success. F1 males were of intermediate weight and F1 males that held territories tended to be lighter than territorial Melbourne males. Melbourne males were more successful than Townsville males because they tended to win escalated encounters, resulting in displacement of territory residents.