Territorial Encounters Research Articles

Loss of complex female song but not duetting in the ancestors of Carolina wrens

AbstractFemale singing and coordinated male–female duetting are often but not always found in the same species. Both behaviors are more common in tropical than temperate songbirds, but few studies have differentiated between the factors selecting for each. Here we investigate the evolution of female vocal complexity and male–female vocal coordination in Carolina wrens (Thryothorus ludovicianus), one of the few non‐tropical members of a songbird family (Troglodytidae) that is well known for producing coordinated male–female duets. Female Carolina wrens are not known to sing; rather, they produce relatively simple, sex‐specific chatters, often during territorial encounters. We analyzed field recordings to show that females coordinate these chatters with male songs at rates similar to those observed in some tropical duetting wren species. We then used phylogenetic comparative methods to show that the evolutionary ancestors of Carolina wrens had female songs that were more acoustically complex than the vocalizations of current females, suggesting past selection against female vocal complexity. Levels of vocal coordination with males, in contrast, have changed relatively little from those of tropical ancestors. Our results suggest that these two aspects of female behavior, acoustic complexity and vocal coordination with males, have evolved independently and have different functions in communication.

Hunters, rangers, cougars, and jaguars: human and nonhuman territories at the Argentine-Brazilian border, 1960s-1990s.

This article aims to understand the role of territorial practices in the interaction between human and nonhuman animals. It focuses on the Iguazú and Iguaçu national parks, established by Argentina and Brazil in the 1930s as nature reserves bisected by an international boundary. In a setting where human-made boundaries overlay natural boundaries, qualitatively different spatial practices clash in the territorial encounters between cougars, jaguars, and humans. The article demonstrates how changes in the border practices of park officials, hunters, and big cats reshuffled the terms of these encounters. The article assesses when, where, and how these encounters between rangers, poachers, and big cats took place, showing how felids challenged the spatial placement and taxonomical categories attributed to them by humans.

Evolutionary and Biomechanical Basis of Drumming Behavior in Woodpeckers

Understanding how and why behavioral traits diversify during the course of evolution is a longstanding goal of organismal biologists. Historically, this topic is examined from an ecological perspective, where behavioral evolution is thought to occur in response to selection pressures that arise through different social and environmental factors. Yet organismal physiology and biomechanics also play a role in this process by defining the types of behavioral traits that are more or less likely to arise. Our paper explores the interplay between ecological, physiological, and mechanical factors that shape the evolution of an elaborate display in woodpeckers called the drum. Individuals produce this behavior by rapidly hammering their bill on trees in their habitat, and it serves as an aggressive signal during territorial encounters. We describe how different components of the display—namely, speed (bill strikes/beats sec–1), length (total number of beats), and rhythm—differentially evolve likely in response to sexual selection by male-male competition, whereas other components of the display appear more evolutionarily static, possibly due to morphological or physiological constraints. We synthesize research related to principles of avian muscle physiology and ecology to guide inferences about the biomechanical basis of woodpecker drumming. Our aim is to introduce the woodpecker as an ideal study system to study the physiological basis of behavioral evolution and how it relates to selection born through different ecological factors.

Sex Differences in Offensive and Defensive Investment in Crayfish Claws

Many animals possess weapons that have evolved to inflict damage to opponents during territorial encounters. Although the offensive capabilities of these weapons are important determinants of contest success, the defensive capabilities of the weapons are also important. However, current theory only accounts for investment into offensive performance, and not defensive endurance. To help better understand these dynamics, we investigated claw strength, cuticle thickness, and injury rates in male and female virile crayfish (Faxonius virilis). To measure the offensive capacity of a claw, we collected the max pinch of 3–5 pinches of each claw using a force transducer. To measure the defensive capacity of the claw, we dissected and measured the cuticle thickness of the carapace and seven sections of the claw: merus, dorsal manus, ventral manus, dorsal dactyl, ventral dactyl, dorsal pollex, and the ventral pollex. Injury rate was determined by visual inspection of the claw. Both male and female virile crayfish engage in aggression over access to both food and shelter. Thus, we expected each sex to invest similarly into the offensive and defensive abilities of their weapons. Interestingly, we found that despite males having proportionally larger claws, the average strength for a given size of the claw was similar between the sexes. Furthermore, we did not detect any sex differences in defensive ability as measured by cuticle thickness and injury rates. Overall, we demonstrated that both male and female virile crayfish invest similarly into the offensive and defensive ability of their claws.Support or Funding InformationNational Science Foundation (NSF) LEAP Scholars program

Reduced tenacity during “high-speed” territorial encounters in the intertidal owl limpet, Lottia gigantea: Agonistic escalation increases risk of wash-off

The dislodging effect of breaking waves is among the critically important factors structuring rocky intertidal communities. Because behavior is so difficult to study in the field, the interaction of wave force with behavior of intertidal organisms is poorly understood. Here, we present a field study of the interaction of breaking waves with the natural behavior of individuals of Lottia gigantea, an intertidal limpet with a complex territorial behavioral ecology. We hypothesized that limpets engaging in fast-moving territorial chase in response to intraspecific contact are more vulnerable to wash-off by a passing wave than are slowly foraging limpets that do not take part in such chase. We measured the lift force required to dislodge limpets while they were engaged in three natural behavioral responses to intraspecific contact in the field: 1.) continued foraging, 2.) retreat, and 3.) territorial pursuit. We divided the measured force-to-remove by aperture area to estimate resistance to wave-induced lift force, or tenacity. Tenacity (Newtons·cm−2) in slowly foraging limpets was 2–4 times stronger than previously reported for moving limpets (retreating at high speed from sea stars). Small foraging limpets showed stronger tenacity than did large limpets. Tenacity was significantly reduced by high-speed territorial and retreat responses, especially in small limpets. We compounded the wash-off probabilities of tenacity during the expected number of high-speed chases in the face of an entire year of reported waves at a nearby ocean buoy, and estimated that limpets should suffer substantially greater mortality (11.5%) than do limpets that refrain from all territorial chase (2.9%). Overall, these data support our hypothesis that dislodgement by breaking waves comprises a significant risk attendant to territorial chase. The fact that limpets nevertheless engage in these chases suggests that the resources gained by this behavior are substantial.

Comparative nest survival of three sympatric loon species breeding in the Arctic

Identifying factors influencing nest survival among sympatric species is important for understanding and managing sources of variation in population dynamics of individual species. Three species of loons nest sympatrically in northern Alaska and differ in body size, life history characteristics, and population trends. We tested the effects of competition, nest site selection, and water level variations on nest survival of PacificGavia pacifica, yellow‐billedG. adamsii, and red‐throated loonsG. stellataon the Arctic Coastal Plain in Alaska. Although overall nest survival rates did not differ between species, the factors influencing nest survival varied. Nest site selection influenced nest survival for Pacific and yellow‐billed loons, with both species having high nest survival when nesting on islands and peninsulas, likely due to a reduction in access by terrestrial predators. However, on mainland shorelines, Pacific loons had lower nest survival than yellow‐billed loons, and used a higher proportion of vegetation mats for nest sites suggesting that their smaller body size makes them less adept at nest defense. Nest site selection did not influence nest survival of red‐throated loons corresponding to our result of no nest site preferences by this species. Initiation date had a strong influence on nest survival for Pacific and yellow‐billed loons with nests laid earlier having higher survival. Pacific and yellow‐billed loon nests were susceptible to flooding due to precipitation, which contrasted with red‐throated loons that nest on smaller lakes with lower water level variations. Competition did not affect nest survival for any of the species likely due to most territorial encounters occurring prior to incubation. The only influence we found on red‐throated loon nest survival was differences among years. Our results indicate that loons chose nest sites based on predation risk and that factors influencing breeding success of closely related species may differ under similar breeding conditions.

Soft songs in male ortolan buntings are used in an aggressive context but are not an aggressive signal

AbstractMany bird species produce low‐amplitude acoustic signals that have been poorly studied in comparison with loud, broadcast songs used for mate attraction and repelling rivals. In some birds, these soft signals were found to be emitted in an antagonistic context and were the most reliable predictor of a subsequent physical attack. The function of this signal is poorly understood, and several hypotheses have been proposed to explain the mechanisms and possible functions of such low‐amplitude signals. The subject of this study is the ortolan bunting, a small passerine species that produces soft songs during territorial defence. In this study, we aim to study whether the soft songs of the ortolan bunting are a signal of increased aggressiveness by testing if they meet the context, prediction and response criteria of aggressive signals. We simulated stranger male intrusion into a focal male territory with three different playback experiments. We found no significant differences in the male responses to the taxidermic model regardless of whether they were or were not producing soft songs in response. The males responded more strongly to loud songs than to soft songs during the simulated intrusions, and the males did not treat soft songs as a predictor of conflict escalation. Although soft songs clearly appeared during territorial encounters and were not present during spontaneous singing before the intrusions, our results did not support the hypothesis that soft songs indicate aggressive character. We suggest that soft songs in the ortolan bunting are intentionally used by birds to modify their intentions or target‐specific individuals within a close range.

High prevalence of Felis catus gammaherpesvirus 1 infection in haemoplasma-infected cats supports co-transmission

Felis catus gammaherpesvirus 1 (FcaGHV1), a potential feline pathogen, has been identified in domestic cats from USA, Asia-Pacific and Central Europe. Transmission of FcaGHV1 during territorial encounters, a route not typical for gammaherpesviruses, is suggested by risk factor analyses from some regions. The aim of this study was to investigate the relationship between FcaGHV1 detection and risk factors, including haemoplasma co-infections, among UK cats to better understand transmission and global distribution of FcaGHV1.FcaGHV1 DNA was detected in blood samples from UK cats (11.56%; 95% confidence interval [CI], 7.47–16.84; n = 199). Logistic regression analyses showed that entire male cats were more likely to be FcaGHV1 positive than neutered male cats (odds ratio, 3.60; 95% CI, 1.22–10.46). Samples positive for DNA from any of three haemoplasma species had 19 times greater odds for testing positive for FcaGHV1 than haemoplasma negative cats in multivariable analyses after adjusting for age, sex and neuter status. Domestic cats in the UK can be infected with FcaGHV1, confirming that this virus is globally endemic. The identification of neuter status as a risk factor for FcaGHV1 detection provides further evidence to support transmission of this virus during territorial encounters and co-transmission with haemoplasmas is suggested.

How memory of direct animal interactions can lead to territorial pattern formation

Mechanistic home range analysis (MHRA) is a highly effective tool for understanding spacing patterns of animal populations. It has hitherto focused on populations where animals defend their territories by communicating indirectly, e.g. via scent marks. However, many animal populations defend their territories using direct interactions, such as ritualized aggression. To enable application of MHRA to such populations, we construct a model of direct territorial interactions, using linear stability analysis and energy methods to understand when territorial patterns may form. We show that spatial memory of past interactions is vital for pattern formation, as is memory of 'safe' places, where the animal has visited but not suffered recent territorial encounters. Additionally, the spatial range over which animals make decisions to move is key to understanding the size and shape of their resulting territories. Analysis using energy methods, on a simplified version of our system, shows that stability in the nonlinear system corresponds well to predictions of linear analysis. We also uncover a hysteresis in the process of territory formation, so that formation may depend crucially on initial space-use. Our analysis, in one dimension and two dimensions, provides mathematical groundwork required for extending MHRA to situations where territories are defended by direct encounters.

Mutual Wattle Ornaments in the South Island Saddleback (Philesturnus carunculatus) Function as Armaments

AbstractMany birds have ornamental traits that are expressed in both sexes. Wattles—colorful fleshy structures that hang from the lower bill—are frequent among birds, but remain poorly understood and are generally presumed to be under sexual selection. The South Island saddleback (Philesturnus carunculatus) is an endangered bird endemic to New Zealand in which both males and females possess wattles. We used behavioral observations, morphological measures, and a playback experiment to investigate the role of wattles in saddlebacks during territorial encounters. Wattles were monomorphic when controlled for body mass, and became engorged with blood in both sexes during visual displays. In a playback experiment using male song, wattle engorgement was significantly associated with territorial intrusions in males but not in females. However, female wattle engorgement was significantly more likely during playback experiments in the absence of their mate, suggesting wattles are used in territorial defense by both sexes. The markedly similar use of wattles by both males and females in visual displays as a response to territorial intrusions supports the hypothesis that these elaborate structures function in part as armaments.

Does a short-term increase in testosterone affect the intensity or persistence of territorial aggression? — An approach using an individual's hormonal reactive scope to study hormonal effects on behavior

In this study, we describe an approach based on an individual's hormonal reactive scope to study short-term effects of hormones on behavior. The control of territorial aggression has been traditionally linked to testosterone. Males of some vertebrate species show an increase in testosterone during territorial interactions and implantation studies suggest that such an increase in testosterone enhances the intensity and persistence of aggression. Here, we tested whether a short-term maximum release of testosterone – based on an individual's hormonal reactive scope – affects the intensity or persistence of territorial aggression in male black redstarts, a bird species in which testosterone does not increase during territorial encounters. An injection with gonadotropin-releasing-hormone (GnRH) induced a physiological peak in plasma testosterone that was specific for each individual (=individual reactive scope). However, such short-term surges in an individual's testosterone concentration did not affect the intensity or persistence of aggression. In conclusion, this study demonstrated (1) that a species that naturally does not increase testosterone during male–male encounters would not benefit from such an increase in terms of being more aggressive, (2) that behavioral studies using GnRH-injections represent a promising approach to study species differences in androgen responsiveness, and (3) that injections of releasing or tropic hormones in general may be a suitable approach to study short-term influences of hormones on behavior. These injections effectively mimic the potential short-term changes in hormones that can occur in the real life of individuals and enable us to study the effects of hormonal changes on behavior or other traits within an ecological and evolutionary framework.

Large‐scale analysis of frequency modulation in birdsong data bases

Summary Birdsong often contains large amounts of rapid frequency modulation (FM). It is believed that the use or otherwise of FM is adaptive to the acoustic environment and also that there are specific social uses of FM such as trills in aggressive territorial encounters. Yet temporal fine detail of FM is often absent or obscured in standard audio signal analysis methods such as Fourier analysis or linear prediction. Hence, it is important to consider high‐resolution signal processing techniques for analysis of FM in bird vocalizations. If such methods can be applied at big data scales, this offers a further advantage as large data sets become available. We introduce methods from the signal processing literature which can go beyond spectrogram representations to analyse the fine modulations present in a signal at very short time‐scales. Focusing primarily on the genus Phylloscopus, we investigate which of a set of four analysis methods most strongly captures the species signal encoded in birdsong. We evaluate this through a feature selection technique and an automatic classification experiment. In order to find tools useful in practical analysis of large data bases, we also study the computational time taken by the methods, and their robustness to additive noise and MP3 compression. We find three methods which can robustly represent species‐correlated FM attributes and can be applied to large data sets, and that the simplest method tested also appears to perform the best. We find that features representing the extremes of FM encode species identity supplementary to that captured in frequency features, whereas bandwidth features do not encode additional information. FM analysis can extract information useful for bioacoustic studies, in addition to measures more commonly used to characterize vocalizations. Further, it can be applied efficiently across very large data sets and archives.

Variation in Trill Characteristics in Tree Pipit Songs: Different Trills for Different Use?

AbstractTransmitting information about singer's quality is an important function of song in many bird species, and this information should be useful in territorial interactions. Fast trills, being physically demanding song structures, are particularly suitable candidates for signalling of quality or aggressive motivation. We have evaluated trill characteristics in songs within a population of the Tree Pipit, a common European songbird with no sexual dimorphism, in which song apparently plays a key role in territory defence as well as mate choice. Two types of relatively fast trills (each of them in multiple variants differing in complexity) were commonly observed in repertoires of Tree Pipit males. Trill rates significantly differed among individuals, suggesting that these song structures may carry information about male quality in this species. We tested by playback experiments whether both trill types are used in territorial encounters. Only one of the trill types was sung by males in response to playback, regardless on the trill type played to them. In an immediate response to playback, they increased the frequency of use of this trill, and also significantly increased the trill rate in comparison with spontaneous songs. This confirmed field observations, suggesting that this trill is important in male–male interactions. On the contrary, the use of the fastest, apparently more demanding, trill type actually decreased after the simulated territorial intrusion. We hypothesize that the latter one is more directed towards females, and that while performance of both trill types may reflect male quality, they are primarily used in different contexts.

Effects of previous intrusion pressure on territorial responses in Nightingales

In territorial animals, establishing and defending a territory against rivals is commonly a prerequisite for successful reproduction. Yet, often, non-territorial males that are seeking to establish their own territory may intrude into occupied territories and persistently challenge residents in order to test their resource-holding potential. Such challenges may have long-term consequences for the territorial behaviour of the residents. Here, we tested whether territorial Nightingales (Luscinia megarhynchos) use information on the intrusion pressure of rivals in territory defence. Using multi-loudspeaker playback experiments, we simulated rivals that either sang from different song perches within occupied territories (persisting intruders) or that immediately left territories after previous intrusions (retreating intruders). In a final playback 1 h later, we then simulated the same rivals singing from a different location at the territory boundary. During this final playback, residents approached the loudspeaker closer, changed their song perches more often, sang more songs in close proximity to the loudspeaker, and sang more trills when rivals were previously simulated as having stayed in their territory without retreating. Our findings show that songbirds can integrate the level of threat from rivals differing in their intrusion behaviours in subsequent territorial encounters. This study emphasises the importance of considering how territorial defence is affected by previous intrusion pressure from rivals.

Vocal signals predict attack during aggressive interactions in black-capped chickadees

Animals use a variety of aggressive signals to mediate territorial interactions. Often these signals can be sufficient to ward off potential rivals, thus minimizing the chance of injury due to physical encounters. Yet not all behaviours produced during territorial interactions are aggressive signals. In this investigation, we examined the aggressive signals of black-capped chickadees, Poecile atricapillus, by determining which signals predict attack on a competitor. We used a recently developed playback protocol involving a loudspeaker and a taxidermic mount to simulate an intruder on males' breeding territories. We examined males' behaviours prior to any physical attack on the mount, both in the minute before attack and the time period preceding this minute. In the minute before attack, we found that gargle calls consistently predicted attack. In the preceding time period, we found that high song rate predicted attack. Surprisingly, we found that attack and the behaviours associated with attack were not significantly correlated with male dominance status. We conclude that song rate and gargle calling behaviour communicate intent to attack during territorial interactions in black-capped chickadees. These results expand our knowledge of aggressive signals during territorial encounters by revealing novel vocalizations used to communicate an animal’s probability to attack an opponent. ► We presented territorial male chickadees with playback and a taxidermic mount. ► Birds that sang at a high rate early in playback attacked the mount. ► Birds produced gargle calls immediately prior to attacking the mount. ► Dominance rank did not predict attack but was associated with overlapping behaviour. ► We conclude that gargle calls and song rate are aggressive signals.

Evidence for scent marking in vervet monkeys?

We used data from two troops of free-ranging vervet monkeys (Chlorocebus aethiops) to assess the proposition that the conspicuous chest rubbing observed in this species constitutes scent-marking behavior. Our data indicate that chest-rubbing behavior is associated with higher-ranking males who are more likely to do so during the breeding season in areas where territorial encounters occur. We found no indication that chest rubbing was triggered directly by encounters between troops. We conclude that these data, in conjunction with reports of chest rubbing from other Old World monkeys, are sufficiently suggestive of scent marking to warrant further, directed research and support the suspicion that olfactory cues remain important to catarrhines in a number of domains.

Regulation of 3β-HSD activity in the songbird brain

Birds show high levels of steroid synthesis in the brain. Steroid biosynthesis in the brain can provide a mechanism for local and rapid changes in steroid levels in particular brain regions. Neural steroidogenic enzymes are regulated on both short and long timescales by both endogenous and environmental factors. Here, we discuss the regulation of one steroidogenic enzyme, 3β-hydroxysteroid dehydrogenase/Δ5-Δ4 isomerase (3β-HSD), which activates the prohormone dehydroepiandrosterone by converting it to a potent and aromatizable androgen, androstenedione. First, brain 3β-HSD mRNA and activity are regulated by developmental stage in nestling Zebra Finches (Taeniopygia guttata). Second, in vitro estradiol rapidly (<10 min) inhibits Zebra Finch brain 3β-HSD activity. Third, restraint stress rapidly (<15 min) regulates brain 3β-HSD activity in adult Zebra Finches and Song Sparrows (Melospiza melodia). Fourth, brain 3β-HSD activity is upregulated during the non-breeding season in wild male Song Sparrows. Fifth, during the non-breeding season, brain 3β-HSD activity is rapidly (<30 min) elevated by territorial encounters in a region-specific manner in male Song Sparrows. Taken together, these studies suggest that brain 3β-HSD is a key factor in the control of avian neurophysiology and behavior.

Field presentation of male secretions alters social display in Sceloporus virgatus but not S. undulatus lizards

Lizards have communicative displays involving primarily vision and chemicals, and recent work suggests trade-offs between these two modalities. In reptiles, little work assesses effects of conspecific chemicals on subsequent signaling behavior. Here, we studied responses to conspecific secretions in two Sceloporus species differing in visual signaling: male Sceloporus undulatus have blue abdominal patches used in aggressive territorial encounters, while Sceloporus virgatus males have evolutionarily lost the patches and have low rates of aggressive display. We measured behavior of free-ranging males following presentation of swabs with conspecific male chemicals from femoral glands and the cloaca, or of clean swabs. For male S. undulatus (blue), neither likelihoods nor rates of behavioral responses differed between swab treatments. In contrast, male S. virgatus (white) presented with secretions had significantly higher likelihood of performing head bob, push-up, and shudder displays, than males in control swab trials. Rates of behavior also differed for S. virgatus, with higher rates of push-up display and tongue flick in trials with conspecific chemicals, but rates of other displays, number of moves, and mean total distance moved did not differ between treatments. Male S. undulatus moved significantly greater distances than S. virgatus, independent of treatment. In sum, male S. virgatus responded to conspecific male chemicals by increasing their low rates of display behavior, whereas male S. undulatus did not alter their already high rates of display or movement following chemical exposure. Chemical signals may play a different role in social signaling in the species with the loss of the abdominal color signal.

Variation on a Theme: Vibrational Signaling in Caterpillars of the Rose Hook-Tip Moth,Oreto rosea

Vibrational communication in hook-tip moth caterpillars is thought to be widely used and highly variable across species, but this phenomenon has been experimentally examined in only two species to date. The purpose of this study is to characterize and describe the function of vibrational signaling in a species, Oreta rosea Walker 1855 (Lepidoptera: Drepanidae), that differs morphologically from previously studied species. Caterpillars of this species produce three distinct types of vibrational signals during territorial encounters with conspecifics — mandible drumming, mandible scraping and lateral tremulation. Signals were recorded using a laser-doppler vibrometer and characterized based on temporal and spectral components. Behavioural encounters between a leaf resident and a conspecific intruder were staged to test the hypothesis that signaling functions as a territorial display. Drumming and scraping signals both involve the use of the mandibles, being hit vertically on, or scraped laterally across, the leaf surface. Lateral tremulation involves quick, short, successive lateral movements of the anterior body region that vibrates the entire leaf. Encounters result in residents signaling, with the highest rates observed when intruders make contact with the resident. Residents signal significantly more than intruders and most conflicts are resolved within 10 minutes, with residents winning 91% of trials. The results support the hypothesis that vibrational signals function to advertise leaf occupancy. Signaling is compared between species, and evolutionary origins of vibrational communication in caterpillars are discussed.

Impact of season and social challenge on testosterone and corticosterone levels in a year-round territorial bird

Plasma testosterone increases during breeding in many male vertebrates and has long been implicated in the promotion of aggressive behaviors relating to territory and mate defense. Males of some species also defend territories outside of the breeding period. For example, the European nuthatch ( Sitta europaea) defends an all-purpose territory throughout the year. To contribute to the growing literature regarding the hormonal correlates of non-breeding territoriality, we investigated the seasonal testosterone and corticosterone profile of male (and female) nuthatches and determined how observed hormone patterns relate to expression of territorial aggression. Given that non-breeding territoriality in the nuthatch relates to the reproductive context (i.e., defense of a future breeding site), we predicted that males would exhibit surges in plasma testosterone throughout the year. However, we found that males showed elevated testosterone levels only during breeding. Thus, testosterone of gonadal origin does not appear to be involved in the expression of non-breeding territoriality. Interestingly, territorial behaviors of male nuthatches were stronger in spring than in autumn, suggesting that in year-round territorial species, breeding-related testosterone elevations may upregulate male–male aggression above non-breeding levels. In females, plasma testosterone was largely undetectable. We also examined effects of simulated territorial intrusions (STIs) on testosterone and corticosterone levels of breeding males. We found that STIs did not elicit a testosterone response, but caused a dramatic increase in plasma corticosterone. These data support the hypothesis that corticosterone rather than testosterone may play a role in the support of behavior and/or physiology during acute territorial encounters in single-brooded species.