The Influence of Relatedness, Neighbourhood and Overall Distance on Colony Mate Recognition in a Polydomous Ant

The ‘dear enemy phenomenon’ predicts that territorial animals respond less aggressively towards more familiar neighbours than towards unfamiliar conspecifics if potential losses to strangers are more costly than potential losses to neighbours. Conversely, territorial animals should respond more aggressively to neighbours, if potential losses to them are more costly than potential losses to strangers. In social insects the question of how colony members distinguish neighbours from strangers, however, is intertwined with the more general question of how colony members discriminate themselves from non‐colony members; both genetic and spatial distance can correlate with levels of inter‐colonial aggression. In this paper I disentangle the role of experience, genetic and spatial distance on inter‐colonial aggression in a polydomous population of Iridomyrmex purpureus. In I. purpureus, aggression is related to the spatial distance between colonies irrespective of genetic similarity. Spatial distance affected aggression in two different ways. First, workers were more likely to exhibit aggression towards alien conspecifics of adjoining rather than non‐adjoining territories, suggesting the opposite of the dear enemy phenomenon. Second, workers were more often aggressive towards conspecifics of more distant colonies, implying that environmental cues play a role in the recognition system of I. purpureus.     

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

Males 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.     

Conditional strategies in territorial defense: do Carolina wrens play tit-for-tat?

Neighboring territorial animals are viewed primarily as intenserivals, but there are also opportunities for cooperation amongcompetitors. Many animals respond less aggressively towardneighbors than to strangers. This phenomenon, termed the "dearenemy" effect, should be stable only when the reduced aggressionis reciprocal. Territory owners should use conditional strategiesin territorial defense, showing reduced aggression toward neighbors who cooperate by respecting territorial boundaries but increasingaggression toward invading neighbors. In this study I examinedthe response of territory owners to playbacks of neighborsat shared boundaries before and after intrusions by that neighboror by strangers. Results showed that territory owners did notincrease their aggression toward defecting neighbors but did increase their aggression toward neighbors after a simulatedintrusion by a stranger. This surprising result might reflectthe long-term relationship between neighboring Carolina wrensand the threat posed by rare intruding strangers.     

Duet codes do not enhance neighbour recognition in two closely related species of duetting neotropical wrens

Numerous studies have shown that territorial animals exhibit less aggression in response to neighbours than to strangers, a phenomenon known as dear enemy effect. The influence of acoustic features, such as song type sharing and repertoire sizes, in neighbour recognition has been widely documented in male songbirds. However, few studies have focused on duetting species, and particularly on those where pairs have pair‐specific duet codes (consistent associations of their individual phrase types). Given that each pair in the population can have a unique repertoire of duet types, duet codes have been hypothesized to enhance discrimination. In this context, we tested for evidence of neighbour recognition and duet code discrimination in two closely related species of neotropical wrens, the riverside wren, Cantorchilus semibadius, and the canebrake wren, C. modestus zeledoni. Although both species have moderately large repertoires, riverside wrens have higher levels of phrase type and duet type sharing across the population. We compared the approach and vocal responses of focal pairs to three playback treatments: neighbours' correct duet type, neighbours' incorrect duet type and a strangers' duet type. We found that riverside wrens displayed a stronger response to the strangers' playback than to both neighbours' playbacks, whereas no differences among treatments were found in canebrake wrens. Given that both species exhibited similar levels of aggression during neighbour playbacks, regardless of whether the correct duet code was used, our findings suggest duet codes do not facilitate neighbour recognition. We conclude that the function of duet codes in these species might be more closely related to intra‐pair communication. Finally, we suggest that the level of dear enemy effect a species exhibits depends on ecological factors that influence the perceived level of threat of territory intruders.     

Male song sparrows have elevated testosterone in response to neighbors versus strangers

Upon hearing a conspecific signal, animals must assess their relationship with the signaller and respond appropriately. Territorial animals usually respond more aggressively to strangers than neighbors in a phenomenon known as the “dear enemy effect”. This phenomenon likely evolved because strangers represent a threat to an animal's territory tenure and parentage, whereas neighbors only represent a threat to an animal's parentage because they already possess a territory (providing territory boundaries are established and stable). Although the dear enemy effect has been widely documented using behavioral response variables, little research has been conducted on the physiological responses of animals to neighbors versus strangers. We sought to investigate whether the dear enemy effect is observed physiologically by exposing territorial male song sparrows (Melospiza melodia) to playback simulating a neighbor or a stranger, and then collecting blood samples to measure plasma testosterone levels. We predicted that song sparrows would exhibit increased testosterone levels after exposure to stranger playback compared to neighbor playback, due to the role testosterone plays in regulating aggression. Contrary to our prediction, we found that song sparrows had higher testosterone levels after exposure to neighbor playback compared to stranger playback. We discuss several explanations for our result, notably that corticosterone may regulate the dear enemy effect in male song sparrows and this may inhibit plasma testosterone. Future studies will benefit from examining corticosterone in addition to testosterone, to better understand the hormonal underpinnings of the dear enemy effect.     

Dear Enemies Elicit Lower Androgen Responses to Territorial Challenges than Unfamiliar Intruders in a Cichlid Fish

In many territorial species androgen hormones are known to increase in response to territorial intrusions as a way to adjust the expression of androgen-dependent behaviour to social challenges. The dear enemy effect has also been described in territorial species and posits that resident individuals show a more aggressive response to intrusions by strangers than by other territorial neighbours. Therefore, we hypothesized that the dear enemy effect may also modulate the androgen response to a territorial intrusion. Here we tested this hypothesis in male cichlid fish (Mozambique tilapia, Oreochromis mossambicus) using a paradigm of four repeated territorial intrusions, either by the same neighbour or by four different unfamiliar intruders. Neighbour intruders elicited lower aggression and a weaker androgen response than strangers on the first intrusion of the experiment. With repeated intrusions, the agonistic behaviour of the resident males against familiar intruders was similar to that displayed towards strangers. By the fourth intrusion the androgen response was significantly reduced and there was no longer a difference between the responses to the two types of intruders. These results suggest that the dear enemy effect modulates the androgen response to territorial intrusions and that repeated intrusions lead to a habituation of the androgen response.     

Kinship,dear enemies,and costly combat: The effects of relatedness on territorial overlap and aggression in a cooperative breeder

Many species maintain territories, but the degree of overlap between territories and the level of aggression displayed in territorial conflicts can vary widely, even within species. Greater territorial overlap may occur when neighboring territory holders are close relatives. Animals may also differentiate neighbors from strangers, with more familiar neighbors eliciting less‐aggressive responses during territorial conflicts (the “dear enemy” effect). However, research is lacking in how both kinship and overlap affect territorial conflicts, especially in group‐living species. Here, we investigate kinship, territorial overlap, and territorial conflict in a habituated wild population of group‐living cooperatively breeding birds, the southern pied babbler Turdoides bicolor. We find that close kin neighbors are beneficial. Territories overlap more when neighboring groups are close kin, and these larger overlaps with kin confer larger territories (an effect not seen for overlaps with unrelated groups). Overall, territorial conflict is costly, causing significant decreases in body mass, but conflicts with kin are shorter than those conducted with nonkin. Conflicts with more familiar unrelated neighbors are also shorter, indicating these neighbors are “dear enemies.” However, kinship modulates the “dear enemy” effect; even when kin are encountered less frequently, kin elicit less‐aggressive responses, similar to the “dear enemy” effect. Kin selection appears to be a main influence on territorial behavior in this species. Groups derive kin‐selected benefits from decreased conflicts and maintain larger territories when overlapping with kin, though not when overlapping with nonkin. More generally, it is possible that kinship extends the “dear enemy” effect in animal societies.     

Adult male collared lizards, Crotaphytus collaris, increase aggression towards displaced neighbours

Differential responses to neighbours and strangers (the dear enemy phenomenon) and individual recognition presumably evolve to reduce costs of territorial defence. Territorial residents have been found to demonstrate reduced aggression towards neighbours wherever they are encountered along that resident's territory boundary except for when the neighbour is displaced to the boundary opposite the shared boundary. In this new location, the displaced neighbour represents a greater threat to the resident's territory ownership, and should be treated as equally aggressive as a stranger. Finding increased aggression towards displaced neighbours has been interpreted as individual recognition, but these results do not provide sufficient evidence to rule out the possibility that the resident sees the neighbour out of its normal context as just another stranger. We tested the hypothesis that territorial collard lizards can individually recognize neighbours and will increase aggression towards them as the threat to territorial ownership increases. Resident males treated neighbours that had been moved to the opposite boundary as equally aggressive as strangers. However, residents responded more aggressively towards strangers than towards neighbours on natural territories (the dear enemy phenomenon) and also in neutral arena encounters. Our results suggest that resident male collared lizards are able to recognize individuals regardless of context and respond to them according to the threat that they pose. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.      

MICRODIALECT AND GROUP SIGNATURE IN THE SONG OF THE SKYLARK ALAUDA ARVENSIS

ABSTRACT

The Skylark Alauda arvensis is a territorial species of open landscape in which pairs settle in stable and adjacent territories during the breeding season. Due to the heterogeneity of the habitat, territories are gathered in patches spaced by a few kilometres, in which each male produces very long and complex flight songs as a part of the territorial behaviour. We showed that, in a given patch, all the males (neighbours) share some particular sequences of syllables in their songs, whereas males settled in different patches (strangers) have almost no sequences in common. Such a phenomenon is known as microdialect. To test the hypothesis that these shared sequences support a group signature, we made playback experiments with “chimeric” signals: songs of strangers where the sequences shared by neighbours were artificially inserted. Behavioural responses to playbacks indicated a neighbour-stranger discrimination consistent with the dear enemy phenomenon, i.e. a reduced aggression toward neighbours compared to strangers. Furthermore, the same level of responses, observed when a “chimeric” song and a neighbour song were broadcast, indicated that shared sequences are recognised and identified as markers of the neighbourhood identity.     

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.       

Rubyspot Territorial Damselflies Behave as “Nasty Neighbors”

Two mutually-excluding hypotheses explain the intensity of aggression between neighbors and their non-neighbors in territorial animals. On one hand, the “dear enemy” hypothesis predicts that territorial animals should be more tolerant towards their neighbors than towards non-neighbors. Conversely, the “nasty neighbor” hypothesis predicts increased aggression towards neighbors than non-neighbors. These different situations depend on who is more likely to be a real competitor, either a neighbor or a non-neighbor, and the intensity of resource competition. Male damselfly of Hetaerina vulnerata defend riverine, mating territories that is the main way to have access to females. These territories are not fixed and so males continuously defend them especially against neighbors. Given this, we tested whether the nasty neighbor principle operates in this species. We monitored a population during an entire mating season, and recorded duration of aggressive behaviors. As a key prediction of the nasty neighbor hypothesis, we expected that such behaviors last for longer when encountering a conspecific neighbor than a conspecific non-neighbor. We also predicted that such duration should be date-dependent as territorial competition could increase in the middle of the season when male density is at its highest. Our results corroborated that aggressive behaviors lasted longer against a neighbor male than a non-neighbor male but there was not effect of date. Thus, neighbors may pose a greater risk and may be a strong selective force than non-neighbors in terms of resource competition. Since neighbor males are continuously trying to widen their territory boundaries (a situation that has been also found in other study systems), an owner male may not even need to recognize his neighbors to fight back.     

Male <Emphasis Type="Italic">Betta splendends</Emphasis> are equally aggressive toward neighbors and strangers

Male Siamese fighting fish, Betta splendens, are known for their ferociousness when defending their territories against male or female conspecific intruders. The aim of this study was to investigate whether this species exhibits the dear enemy phenomenon, where territorial males would be less aggressive toward neighbors with already established territories than toward complete stranger males. In experiment 1, a male Betta was placed in an aquarium. A second male was placed in a glass jar that was fitted in one corner of the aquarium. After 24 h, a cover was placed around the jar, and then removed after 1 h. Alternatively, the jar male was replaced with a different male of a different color while the jar was covered. The frequency and duration of opercular expansion by the aquarium male were recorded. In experiment 2, two male Bettas were placed, each in a half of a large aquarium that was equally divided by a clear, perforated Plexiglas divider. After 24 h, one male (intruder) was transferred into the other male’s (resident) half. In another variation of the experiment, the intruder was a stranger male Betta that the resident male had never encountered before. The opercular expansion and duration were scored for the resident male. The results indicated that male Siamese fish reacted similarly to familiar and stranger males. This lack of dear enemy effect in Siamese fish could be due to an inability to discriminate between neighboring males and non-neighboring males. Alternatively, territorial males could be equally aggressive to all intruders because all intruders represent equal danger.     

Encounter-induced hostility to neighbors in the ant Pristomyrmex pungens

Field observations have demonstrated that internest hostilityis negatively correlated with the distance between nests inthe Japanese queenless ant, Pristomyrmex pungens. This runscounter to the "dear enemy" phenomenon. This result led us tohypothesize the existence of encounter-induced hostility inP. pungens. We created "neighbor(s)" and "stranger(s)" by anexperimental method and tested the ant's ability to discriminatethe neighbors from strangers. The results indicated that theant could distinguish the neighbors from the strangers and displayedsignificantly stronger hostility toward the neighbors. The recognitionof neighbors was quickly established after a few encountersand was maintained for at least 10 days after the most recentencounter. Nest mates without direct encounter experience withneighbors did not show hostile behavior toward neighbors. Thesefindings suggest that information about neighbors (probablycolony odor) is not transmitted to nest mates within the colonies.Aggressiveness toward the neighbors appears to be caused andmaintained on the basis of individual memories from direct contact.It may be adaptive for a species that changes nest sites frequentlyto discriminate strangers from neighbors and selectively attackthe latter.     

Duetting behavior in a Neotropical ovenbird: sexual and seasonal variation and adaptive signaling functions

Duetting is a collective behavior and might have multiple functions, including joint territory defense and mate guarding. An important step toward understanding the adaptive function of bird song is to determine if and how singing behavior varies seasonally. However, seasonal patterns for duetting species are different from the pattern described for species in which only the male sings, because song function may vary according to sex, singing role (initiator vs responder) and level of duet organization (individual vs pair). We investigated whether patterns of seasonal variation in duetting depends on these factors, which would suggest different interpretations of song function. We studied social pairs of a Neotropical bird species (rufous hornero Furnarius rufus) for seven consecutive months, recording vocal and territorial behaviors. Overall, partners coordinated 61% of their songs into duets and many song traits (song initiation rate, song output and duet rate) peaked in territorial contexts. Males engaged in territorial interactions with strangers more often, initiated more songs, and answered proportionately more of their partners’ songs than females. Male song initiation rate peaked during the pre‐ and post‐breeding stages, whereas females initiated more songs during the non‐breeding season. Both sexes answered partner songs faster and at higher rates during the pre‐breeding and female fertile stages. Partners duetted at a higher rate during the pre‐ and post‐breeding stages. Finally, song initiation rates and duet rate, but not song answering rates, correlated with frequency of territorial interactions with strangers. Although our findings indicate that song function may vary with sex, singing role and level of duet organization, our results suggest that in general duet functions to defend common territories and as a mutual mate guarding strategy in the rufous hornero.     

Neighbor–Stranger Discrimination in Concave-Eared Torrent Frogs, Odorrana tormota

The dear enemy phenomenon in which animals discriminate familiar neighbors from unknown strangers, and respond more aggressively to strangers is well established in various social animals, especially in songbirds and mammals. So far, very few studies of neighbor–stranger discrimination have been carried out in amphibians and the results have been mixed. Thus, it is unclear whether this phenomenon exists commonly in frogs and toads, and whether it is exhibited by species with large vocal repertoires. We conducted acoustic playback experiments with male concave-eared torrent frogs ( Odorrana tormota , a species with an unusually large vocal repertoire) kept in a tank in a quiet room to investigate whether or not they can discriminate strangers from neighbors acoustically. Nine of the 14 males tested showed evoked vocal responses to the calls from strangers, but none to calls from neighbors; vocal response to the calls from strangers was accompanied by aggressive motor activity. These results demonstrate that male O. tormota possess the ability to discriminate neighbors from strangers acoustically. Odorrana tormota therefore joins three ranid species ( Rana catesbiana , Rana clamitans , Rana dalmatina , all known to have a comparatively small and stereotyped vocal repertoires) as the only anurans demonstrated to have this ability. Given the difference in signaling complexity between these frog species, the salient acoustic features used for discriminating neighbors and strangers are likely to be quite distinct.     

Friend or foe? Differential aggression towards neighbors and strangers in the ant Liometopum microcephalum (Hymenoptera: Formicidae)

Intra- and interspecific aggression is quite common in ants, from occasional conflicts to large-scale territorial disputes. The “nasty neighbor” phenomenon describes the differential aggressive treatment of neighbors versus foreign intruders. Due to the fact that workers of a given colony meet rival neighbors more often at food resources, they treat them as threats to their colony. The reverse can also happen: the “dear enemy” effect arises when an already known rival is treated less aggressively due to accommodation, than an unknown distant one. In the current study, we analyzed the effect of distance on the aggressiveness of Liometopum microcephalum, a territorial arboricolous ant, towards non-nestmates in two large populations. Our results show that aggression did not increase with distance, but it was higher among neighbors than among workers coming from distant nests. The results of the study are consistent with the nasty neighbor scenario, and do not support the hypothesis that the studied populations would be polydomous systems of interconnected nests.     

Relative threat and recognition ability in the responses of tropical mockingbirds to song playback

It has been suggested that individual recognition based on song may be constrained by repertoire size in songbirds with very large song repertoires. This hypothesis has been difficult to test because there are few studies on species with very large repertoires and because traditional experiments based on the dear enemy effect do not provide evidence against recognition. The tropical mockingbird, Mimus gilvus, is a cooperative breeder with very large song repertoires and stable territorial neighbourhoods. The social system of this species allowed us to test individual recognition based on song independently from the dear enemy effect by evaluating male response to playback of strangers, neighbours (from shared and unshared boundaries), co-males (i.e. other males in the same social group) and own songs. Although subjects did not show a dear enemy effect, they were less aggressive to co-males than to all other singers. Our results suggest that recognition in tropical mockingbirds (1) does not simply distinguish between familiar and unfamiliar singers, (2) requires a small sample of both songs and song types, (3) does not rely on individual-specific sequences of song types and (4) is not likely to rely on group-specific vocal signatures potentially available in cooperatively breeding groups. We conclude that this is a case of true recognition and suggest that the lack of a dear enemy effect in this and other species with large repertoires may relate to the role of song in mate attraction and the perception of neighbours as a threat to future paternity.     

Are Androgens Related to Aggression in House Wrens?

Elevated circulating testosterone levels are hypothesized to allow male animals to direct resources into territorial and mating behaviors at the expense of reducing paternal care of offspring. For this hypothesis to apply, testosterone must facilitate territorial/mating behaviors and have antagonistic effects on paternal care, but this pattern has only been supported in some, not all, species. I tested whether androgens correlate with aggressive behaviors in male house wrens ( Troglodytes aedon), a double‐brooded species where paternal and aggressive behaviors overlap temporally. House wrens may therefore benefit from having a hormonal mechanism that allows males to rapidly change behavioral states. However, I found no evidence that androgens (testosterone and 5α‐dihydrotestosterone) relate to aggression in house wrens: Androgens did not increase in response to playback, and endogenous‐circulating androgens were not correlated with how aggressively males responded to those playbacks. Moreover, androgen levels were low during the pre‐breeding stage of the second brood, when many males establish new territories and attract new mates. This study adds to a growing body of the literature suggesting that the relationship between circulating androgens and aggressive behavior is more complex than originally thought.     

Factors Affecting Interspecific Aggression in a Year‐Round Territorial Species,the Jewel Damselfish

Vertebrates live in complex species networks in which interspecific interactions are common. In some contexts, the aggressive behaviours shown in these interspecific interactions are very similar to those shown in intraspecific interactions. It is still an open question whether intra‐ and interspecific aggression share common causality. We studied a year‐round territorial species the jewel damselfish, (Plectroglyphidodon lacrymatus), which cultivate algae they feed on. Territory holders aggressively defend these algae that are an attractive resource for many other species. In this study, we recorded territorial aggression in free‐living individuals and recorded aggressive responses to a standardized territorial intrusion test in captive individuals. Field observations indicated that territorial aggression was selectively targeted towards food competitors. Independent of the size of the species, aggression was more frequent towards common species around their territories. This relationship was confirmed experimentally by confronting the jewel damselfish with novel objects to which the subjects were exposed either frequently or rarely. We suggest that jewel damselfish have to learn which species are competitors and therefore should be chased. In a standardized intrusion test with captive individuals, no significant differences were found in territorial responses towards intra‐ or interspecific intruders. Neither territorial aggression nor the intrusion showed any relationship with plasma androgen levels. Together, these data suggest that experience might be more important in non‐seasonal territorial aggression than circulating hormonal factors.     

Male territorial aggression does not drive conformity to local vocal culture in a passerine bird

In many songbird species, young individuals learn songs from neighbors and then settle nearby, thus creating neighborhoods of conformity to local vocal culture. In some species, individuals appear to postpone song learning until after dispersal, possibly to facilitate conformity to local dialects. Despite decades of study, we still lack a consensus regarding the selective pressures driving this delayed song learning. Two common hypothetical benefits to conformity, and thus delayed song learning, are rooted in territorial interactions; individuals preferentially produce local song either to avoid detection as new arrivals (deceptive mimicry) or to be more effectively recognized as conspecific territory holders. The dickcissel (Spiza americana) is an ideal species in which to study these hypotheses. Males of this species appear to delay song learning until they arrive at their first adult territory, each individual sings a single song type, and conformity to the local song culture is high. Using playback, we contradicted both of the territorial hypotheses described above; male dickcissels did not respond differentially to local vs foreign song playback treatment. We are confident in this lack of difference because dickcissels clearly responded less strongly to a third treatment, neighbor song, than to the other two treatments, demonstrating sufficient power in our experimental design (and providing the first evidence of the dear‐enemy effect in dickcissels). Our results raise the question of why dickcissels respond equally aggressively to both local and foreign songs when other bird species often show reduced aggression toward foreign song. If reduced aggression to foreign song is not ubiquitous in species that achieve conformity through delayed learning, then selection from aggressive territorial interaction seems unlikely to be a general explanation for such delayed learning. Reduced aggression in response to foreign songs in other species may be due to reduced exposure to the stimulus of foreign song or to different cost‐benefit trade‐offs when responding to songs that deviate from the local average.