Dear Enemy Relationship Research Articles

Horneros consider their neighbors as precious foes regardless of territory size and human disturbance

Research on neighbor-stranger discrimination theory has revealed the significance of social context and biological traits affecting the mechanisms that drive social discrimination, such as the dear enemy or nasty neighbor effects (strangers or neighbors more threatening, respectively). Nevertheless, the effects of territory size and human activity on neighbor-stranger experiments have yet to be explored. By examining behavioral responses to spontaneous duets of neighbors and playbacks of strangers’ duets, we tested whether rufous horneros (Furnarius rufus) in smaller territories show heightened aggression, responding more strongly to strangers and less to neighbors than those in larger territories. This could be expected because birds in larger territories might struggle to differentiate competitors due to limited interactions, hindering familiarity with neighbors. Meanwhile, birds in smaller territories are likely to treat neighbors as dear enemies due to the need to minimize territorial costs caused by presumed frequent intrusions or to protect limited resources. Contrary to predictions, rufous horneros responded more strongly to strangers than neighbors, regardless of owner territory sizes. This suggests that the presumed higher intruder frequency in smaller territories does not necessarily lead to adjusted dear enemy relationships. Yet, small territory holders exhibited heightened vocal responses to duets of unfamiliar intruders, indicating a stronger 'dear enemy' effect compared to birds with larger territories. We also tested whether dear enemy relationships would be heightened during weekends. This is linked to the difficulty urban birds might face in distinguishing neighbors from strangers during high human activity days (i.e., on weekdays), due to factors like noise masking intruder acoustic cues and heightened vigilance. Territorial owners exhibited consistent dear enemy behavior towards neighbors, regardless of our proxy for human activity. This underscores their ability in identifying competitor identities within urban settings.

Vocal behaviour reveals asymmetries in neighbour relationships in a semi-colonial raptor, the Eurasian Scops Owl Otus scops

Abstract Territorial animals often reduce aggression towards familiar neighbours compared to unfamiliar conspecifics. However, variation in the response to different neighbours is less known. In this work, I examined the territorial behaviour of male scops owls during countersinging interactions with two familiar neighbours and I asked whether vocal behaviour of the focal male reflected dear-enemy relationships. Analysis revealed that the focal male’s vocal frequency was associated with (1) the degree of instability of the territory boundary shared with a neighbour and (2) the motivation to persist in the dyadic interaction with that neighbour. Patterns of movement directed to specific individuals suggest that scops owls do discriminate between neighbours. A case of partial territory takeover was observed that was accompanied by temporal changes in vocal frequency in one of the opponents, confirming that vocal frequency is a flexible, context-dependent feature of the relationship of neighbouring scops owls.

Testing the dear enemy relationship in fiddler crabs: Is there a difference between fighting conspecific and heterospecific opponents?

Reduction of aggressiveness toward familiar neighbors, when compared to aggressiveness toward unfamiliar strangers, can decrease the costs of territory defense. This phenomenon is known as the “dear enemy effect”. Individuals may shift their aggressiveness toward neighbors or strangers from the same or different species, depending on the relative threat associated with different opponents. Therefore, a reduced level of aggressiveness between heterospecific neighbors is expected in relation to conspecific intruders, since the latter compete not only for territory, but also for mates. Herein we investigated the occurrence of the dear enemy effect in territorial fights between conspecific pairs of Leptuca leptodactyla and heterospecific pairs of L. leptodactyla versus Leptuca uruguayensis. Across both conspecific and heterospecific fights, medium- and high-intensity fight components were more used in resident–stranger than in resident–neighbor fights. Thus, residents showed a dear enemy response, regardless of opponent species. Moreover, conspecific fights induced a greater number of low- and medium-intensity fight components than did fights between heterospecifics, both neighbors and strangers. Finally, conspecific resident–stranger fights took longer than heterospecific resident–stranger fights. Our results indicate that fiddler crabs adjust their territorial response according to the species and resident status of intruders, consistent with the risks posed by different intruder types.

Tit for Tat in the Dear Enemy Relationship Between Territorial Females of a Cichlid Fish

Many territorial animals reduce aggression toward their neighbours once territorial boundaries are established. This relationship is called the dear enemy phenomenon, hypothetically based on a conditional strategy like tit for tat (TFT). However, studies on territorial animals such as male songbirds do not fully support this hypothesis. We tested the TFT hypothesis in females of the territorial cichlid Neolamprologus pulcher, which exhibits dear enemy relationships, under laboratory conditions. Focal fish attacked invading neighbours as frequently as invading strangers, but they immediately stopped attacking the dear neighbour after the neighbour returned to its own territory, whereas they kept attacking strangers even after they stopped invading. These responses of territory owners are consistent with the predictions of TFT theory. Interestingly, fish were likely to remain vigilant toward the neighbour after its invasion and subsequent return to its own territory.

Territorial fish distinguish familiar neighbours individually

Abstract True individual recognition (TIR), the ability to distinguish multiple familiar members individually, is more elaborate than class-level recognition, and evidence for the ability to perform TIR is reported from primates, some other social mammals, birds and lizard in vertebrates. These animals exhibit a highly social structure, wherein TIR is essential for their social interactions. Such high sociality has been documented in fish, but clear evidence of TIR has been limited. The cichlid, Neolamprologus pulcher, a cooperative breeder that guards a territory, exhibits the dear enemy relationship. Here, we show that this fish distinguishes two familiar neighbours individually, i.e., TIR ability, using one-way mirrors in experimental tanks. Focal fish established the dear enemy relationship with two neighbours, NA and NB, and displayed limited aggression towards these familiar neighbours. However, their aggressiveness towards neighbour NB increased when they were shifted from the original side of the tank after NA was removed, suggesting that they distinguished NB from NA or regarded NB as a stranger. Interestingly, this aggression level against the shifted neighbour NB largely decreased within 1 min. This decrease contrasted with the longer and more frequent aggressiveness towards unfamiliar strangers. These results suggest that focal fish recognised neighbour NB as a familiar stranger but probably punished NB that moved beyond its territory, that is, betrayed the dear enemy relationship. We prevented the effects of the behavioural reactions of exposed individuals using a one-way mirror. Thus, we conclude that this fish species displays TIR and discuss that TIR is prevalent in territorial animals in which the dear enemy effect is common.

Territorial olive frogs display lower aggression towards neighbours than strangers based on individual vocal signatures

Some territorial animals display a form of social recognition in which they direct low levels of aggression towards established neighbours, but maintain greater readiness to respond aggressively towards unfamiliar individuals. In many taxa, such as songbirds, this so-called ‘dear enemy’ effect involves discrimination between neighbours and strangers based on individually distinctive vocal signatures. Although most anuran amphibians (frogs and toads) are highly vocal, and many are also territorial, we know very little about neighbour–stranger discrimination in this group. In the present study of the olive frog, Babina adenopleura (Ranidae), we show that the vocal signals of males are individually distinct, and that territory holders use this information to direct lower levels of aggression towards their nearby neighbours. Analyses of individual variation in advertisement calls revealed many individually distinctive spectral and temporal acoustic properties, with spectral properties contributing most towards statistical discrimination among individuals. In a field playback experiment that simulated territorial intrusions, territorial males had higher thresholds for producing aggressive calls in response to the advertisement calls of their nearby neighbours compared with those of strangers. A simple model based on sound attenuation due to spherical spreading estimated that males responded aggressively to strangers at distances that were approximately twice as far away as for neighbours and that were similar to intermale distances recorded in the field. Together, results from this study indicate that territorial male olive frogs develop vocally mediated dear enemy relationships with their nearby neighbours. These results highlight the potential for convergence in social recognition systems across diverse taxa.

A dear enemy relationship in a territorial cichlid: evidence for the threat-level hypothesis

Despite competing for resources such as space, food and mates, many territorial animals are less aggressive towards neighbours who rarely go beyond their territorial boundaries. This so-called dear enemy phenomenon is advantageous in territorial defence, but it has not been well studied in fish. In this work, we tested the ‘correct–incorrect boundary paradigm’ of the dear enemy phenomenon using the territorial cichlid fishNeolamprologus pulcher, which exhibits dear enemy relationships. When the fish was placed in a small experimental tank, in which fish established its territory, it was initially very aggressive against a neighbouring fish in an adjacent tank, but the aggression level decreased rapidly (within 4 days). When the tank containing the neighbour was shifted to the opposite side, the focal fish was more aggressive than the day before, but it exhibited less aggression than it did against a stranger placed on the shifted side. This lower level of aggression suggested that the focal fish did not regard the shifted neighbour as a stranger. Our observations provide support for the threat-level hypothesis, according to which territory owners will modulate aggression intensity based on the threat level.

Dear enemy relationships in the subterranean rodent Ctenomys talarum: the role of memory of familiar odours

Individual recognition is expected to enhance fitness by allowing animals to direct appropriate behaviours to specific individuals during interactions with conspecifics. Reduced aggression towards territorial neighbours (‘dear enemy phenomenon’) is based on the assumption that strangers lacking territories pose a greater threat than territory-holding neighbours. Based on the ability of the subterranean rodent Ctenomys talarum (tuco-tuco) to distinguish between familiar and unfamiliar conspecific odours, I assessed whether males, the more aggressive sex, show dear enemy relationships and whether social experience with odour donors affects the memory of conspecific odours. Male–male contests in the laboratory were used to compare the aggressive behaviour of pairs of males. Familiar male tuco-tucos responded less aggressively during contests than unfamiliar males, providing evidence of the dear enemy relationship in C. talarum . Memory for familiar odours was affected by social experience since discrimination of known from novel odours lasted longer when males encountered each other in dyadic contests following familiarization with odours. Familiarity by odour cues would represent an important mechanism mediating neighbour recognition and territorial behaviour for tuco-tucos in the wild; intruders may represent a threat of great consequence for territory-holding individuals since they represent the potential loss of their burrow system and their priority of access to neighbouring females.

When to be a dear enemy: flexible acoustic relationships of neighbouring skylarks, Alauda arvensis

Numerous territorial species are less aggressive towards neighbours than strangers. This tolerance towards neighbouring conspecifics, termed the ‘dear enemy’ effect, seems to be a flexible feature of the relationship between neighbours, and has been shown to disappear in some species after experimental or natural modifications of the context. However, the maintenance over time of this singular relationship has been poorly studied. In this study, we followed the change of dear enemy relationships during the breeding season in a territorial songbird with a complex song, the skylark. We examined in the field the response of territory owners to playbacks of neighbour and stranger songs at three periods of the breeding season, corresponding to three ecological and social situations. Results showed that neighbours were dear enemies in the middle of the season, when territories were stable, but not at the beginning of the breeding season, during settlement and pair formation, nor at the end, when bird density increased owing to the presence of young birds becoming independent. Thus, the dear enemy relationship is not a fixed pattern but a flexible one likely to evolve with social and ecological circumstances.

Disruption of Dear Enemy Recognition Among Neighboring Males by Female Leon Springs pupfish, Cyprinodon bovinus

AbstractMales defending territories often settle into adjacent areas, sharing a common border that is maintained by a reduced level of aggression known as dear enemy recognition. While social conditions may affect the dear enemy relationship among males, what role females play, if any, is unclear. In a field study of the highly promiscuous Leon Springs pupfish, Cyprinodon bovinus, we asked whether females influenced this relationship of neighbors to their advantage. We observed 16 territorial residents, mapping the precise location of each male's behaviors within its territory. Resident males engaged in less aggression against neighbors compared with intruders, and neighbors intruded less deeply into the residents’ territories than intruders. Despite this locality restriction, neighbors were responsible for as many spawning interruptions as intruders. Females did not spawn randomly in the males’ territories, nor did they spawn near territory centers where aggression was low. Rather, females were more likely to settle and spawn in the outer half of the territories where competition among males was highest. When a neighbor entered a resident's territory to interrupt a spawn, the female was more likely to leave the resident's territory for the neighbor's than to remain. These observations suggest that the female used the intrusion by the neighbor to engage the resident and interrupt the spawn as a measure of this male's quality and that, while neighboring males benefit from the presence of dear enemy recognition, females benefit from its disruption.

Responses to neighbours and non-neighbours in the buff-banded rail (Gallirallus philippensis): no dear-enemy relationships

Territorial individuals often respond less aggressively to intrusions by their neighbours than to intrusions by unfamiliar individuals. This commonly observed strategy, the dear-enemy phenomenon, is thought to minimise the costs associated with territory defence. This study determined whether an insular population of territory-holding buff-banded rails (Gallirallus philippensis) exhibits dear-enemy relationships and whether males and females differ in their responses to neighbours and non-neighbours. Playback techniques were used to examine and compare the vocalisations and movements of focal individuals in response to the territorial advertisement calls of their neighbours and of unfamiliar individuals (non-neighbours). Results showed that focal birds did not respond differently to the calls of neighbours and non-neighbours; thus, no evidence for the dear-enemy phenomenon was found in this species. We suggest that this result is due to the significant threats posed by neighbours to territory owners in this territorial system, in addition to a high level of territorial instability in the population. Males and females were shown to differ qualitatively in their general territorial response to intruders but not in their relative responses to neighbours and non-neighbours, suggesting that the relative threats posed by neighbours and non-neighbours do not differ between the sexes.

When are neighbours ‘dear enemies’ and when are they not? The responses of territorial male variegated pupfish, Cyprinodon variegatus, to neighbours, strangers and heterospecifics

Dear enemy recognition reduces the costs of territorial defence in some species, but not others, when a neighbour is more threatening to a resident's fitness than an intruder. I asked whether dear enemy effects were fixed in a particular species, or if the reduced aggression between a resident and neighbour was disrupted by the presence of potential mating opportunities. Observing variegated pupfish, Cyprinodon variegatus, in the field and in the laboratory, I examined the effects of a female's presence in a male's territory on residents' aggressive responses to conspecific neighbours and strangers as well as heterospecific opponents. Although reduced aggression consistent with dear enemy recognition was seen between conspecific neighbours in the absence of females, the presence of a female in a male's territory instigated comparably greater aggression between the neighbours. No reduction in aggression was seen between pupfish males and heterospecific opponents. These findings suggest that dear enemy recognition may be a flexible, rather than a fixed, feature of the relationship of neighbouring conspecific males. Despite the disruption in dear enemy recognition caused by a female, residents in the laboratory faced with neighbours spent more time associating with the female than residents faced with strangers. This allowed the residents to secure as many spawns as did males who had been faced with no competitor. Residents faced with any other type of opponent had reduced reproductive success, suggesting that the dear enemy relationship between residents and neighbours is more complex than simply a reduction in aggression. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.

Elevated predation risk changes mating behaviour and courtship in a fiddler crab

The fiddler crab, Uca beebei, lives in individually defended burrows, in mixed-sex colonies on intertidal mud flats. Avian predation is common, especially of crabs unable to escape into burrows. Mating pairs form in two ways. Females either mate on the surface at their burrow entrance ('surface mating') or leave their own burrow and sequentially enter and leave ('sample') courting males' burrows, before staying in one to mate underground ('burrow mating'). We tested whether perceived predation risk affects the relative frequency of these mating modes. We first observed mating under natural levels of predation during one biweekly, semi-lunar cycle. We then experimentally increased the perceived predation risk by attracting grackles (Quiscalus mexicanus) to each half of the study site in two successive biweekly cycles. In each experimental cycle, crabs were significantly less likely to mate on the side with more birds. Moreover, on the side with elevated predation risk, the number of females leaving burrows to sample was greatly reduced relative to the number of females that surface-mated. Males waved less and built fewer mud pillars, which attract females, when birds were present. We discuss several plausible proximate explanations for these results and the effect of changes in predation regime on sexual selection.

Dear Enemies and the Prisoner's Dilemma: Why Should Territorial Neighbors Form Defensive Coalitions?

Game-theoretic arguments are used to derive two new hypotheses to explain why territorial residents so consistently defeat potential usurpers. Both hypotheses are based on help from established, familiar neighbors. The first hypothesis follows simply from Krebs' (1982) assertion that the value of a territory to a usurper must be decremented by the costs of negotiating dear-enemy relationships with the remaining neighbors. An implication is that the remaining neighbors will also have to pay these renegotiation costs if the usurper succeeds. The first hypothesis is that it may benefit a territorial animal to help its established neighbors defend so it can avoid having to renegotiate territorial boundaries with a new, unfamiliar neighbor. This hypothesis assumes net positive benefits to helping without requiring reciprocation. The second hypothesis requires reciprocation to compensate for immediate net costs of helping. An animal should help its neighbors fight off usurpers only if the neighbors will reciprocate. This hypothesis is based on the prisoner's dilemma game and builds on Axelrod's (1984) work. Cooperative defense (reciprocal help) can be an evolutionarily stable strategy (ESS) if several conditions are met. One critical condition is that the relationship between neighbors is relatively stable. Cooperative defense should help established neighbors retain their territories, and should therefore be a cause, as well as a consequence of stability. It is suggested that the necessary conditions are not very restrictive, that they are often met in nature, and that shared defense is observed but not recognized as such.