Wiley: Ethology: Table of Contents

She Doesn't Whisper: Female‐Prominent Stridulation Shaped by Morphology in a Buthid Scorpion and Insights on Its Function

Mon, 25 May 2026 00:00:00 -0700

Sexual dimorphism and stress-induced stridulatory responses in Jaguajir rochae (Borelli, 1910). Females exhibited greater absolute pectinal size and higher sound pressure levels, whereas males showed higher pectinal allometric ratios relative to body size, lower sound frequencies, and shorter delta times. Stridulatory responsiveness was observed under low mechanical stress (a), high mechanical stress (b), and low mechano-chemical stress associated with chemical cues from the predator Rattus norvegicus (Berkenhout, 1769).

ABSTRACT

Stridulation, acoustic communication produced by friction between specialized body structures, is a poorly studied antipredator mechanism. Scorpions may display multiple defensive responses, yet acoustic signaling in such defensive context remains poorly studied. Given the sexual dimorphism commonly observed in scorpion body size and pectines, the latter, which may be involved in sound production, could vary morphologically and result in acoustic differences. We hypothesized that (1) stridulatory apparatus of the scorpion Jaguajir rochae (Borelli, 1910) is sexually dimorphic, (2) sexual dimorphism in stridulatory structures affects acoustic parameters, and (3) stridulatory responses vary with stress, tested via (2.1) mechanical and (2.2) mechano-chemical stimulation. Sound-producing structures and acoustic parameters were measured and stridulation was tested under high/low mechanical stress and mechano-chemical stress, the latter using chemical cues from a mammalian predator. Females exhibited larger pectinal structures, whereas males showed a higher allometric ratio relative to body size. Stridulatory signals in J. rochae showed sexual differentiation primarily in delta time, dB Sound Pressure Level, and low frequency, as revealed by Principal Component Analysis, what explains 38.7% of acoustic variance. Females produced longer and more intense signals, whereas males exhibited slightly higher peak frequencies. Yet, the occurrence of stridulatory responses was similar across different stress treatments. These findings reveal that sexual dimorphism in stridulatory apparatus influences acoustic parameters and that stridulation in J. rochae can be triggered by mechanical stimulation, supporting its role as a defensive behavior. This study provides the first evidence of sex-specific acoustic variation in scorpion stridulation and elucidates its function as an antipredator strategy.

Avian Scavengers Modify Vigilance Across Visits to Foraging Sites

Alex Blanche, Michael R. Conover, S. Nicole Frey — Thu, 21 May 2026 03:30:59 -0700

We researched changes in vigilance in three avian scavengers using trail cameras at carcasses. Turkey vulture and golden eagle vigilance negatively correlated with the individual's aggressive behavior, and golden eagle vigilance was positively correlated with group size, both attributes that vary across foraging visits. California condor vigilance was not correlated with any variable tested, including attributes that change at a carcass (spatial) scale or at a visit (temporal) scale. These included understory cover, canopy closure, distance to roads, carcass consumption, and temperature, among others.

ABSTRACT

The ability of wildlife to perceive the riskiness of a foraging site accurately and modify their behavior accordingly is crucial to feeding safely. Especially for avian scavengers, carrion is a risky food source, as predators defend their kills and mesocarnivores are attracted to carcasses. Vigilance is one strategy to balance foraging and safety. However, spending time vigilant makes feeding less efficient and can increase the total amount of time required at a carcass. We recorded videos of California condors (Gymnogyps californianus), golden eagles (Aquila chrysaetos), and turkey vultures (Cathartes aura) at 61 naturally occurring and staged carcasses May–September 2022 and 2023 using trail cameras. We assessed variables that were hypothesized to impact the proportion of time spent vigilant by each species at both carcass and visit scales and compared these across species. Carcass-level models did not improve upon the null models tested, perhaps because carcass-level attributes determine attendance, rather than altering behavior. Visit-level models performed better than null models for vultures and eagles. Both top models were based on current interactions at the carcass, suggesting similar perceptions of risk at foraging sites. Vulture and eagle vigilance were negatively correlated with the aggression displayed by that individual, and eagle vigilance was positively correlated with numbers of individuals simultaneously present.

Food, Affection and Gaze: Which Cues Do Free‐Ranging Dogs Prioritise for Engaging With Humans?

Tue, 19 May 2026 21:22:29 -0700

Free-ranging dogs interact with humans regularly on the streets, depending on them for food and forming social bonds. We conducted an experiment to understand the hierarchy of human cues, if any, as perceived by the dogs. The rewards offered were high value food (chicken), low value food (biscuits) and petting, with and without the human gazing at the dog. The dogs prioritised the chicken over all other cues, but petting was as important as biscuits. Gazing by humans, signifying attention, was a subtle reinforcer for the dogs. This study elucidates how important human contact is for free-ranging dogs.

ABSTRACT

Free-ranging dogs (Canis lupus familiaris) constitute the majority of the global dog population and rely heavily on human-derived resources. Studies show different levels of responses to various cues like food, petting and gazing by humans. However, the relative importance that dogs associate with these rewards, driving their interactions with unfamiliar humans, remains understudied. Understanding how these dogs prioritise different potential rewards, ranging from food to social contact, can offer insights into their adaptive strategies within human-dominated ecosystems and help to reduce conflict. We investigated the motivational value of different reward types in 150 adult free-ranging dogs in West Bengal, India. Using a between-subjects design, unfamiliar experimenters offered one of five rewards: high-value food (chicken), low-value food (biscuit), social interaction (petting), human gaze only or human presence only. Motivation was assessed by measuring the number of rewards accepted, approach latency, duration of proximity and behaviour via a Socialisation Index (SI). High-value food was the most potent driver of approach behaviour and sustained proximity. While petting elicited higher SI scores, indicating affiliative engagement, it was associated with more rapid satiation than food. Human gaze alone functioned as a subtle reinforcer compared to passive presence, maintaining dog attention longer than presence alone. These findings suggest that free-ranging dogs prioritise high-energy intake over social interaction with strangers, consistent with an optimal foraging strategy. This behavioural flexibility enables them to balance energy needs against potential risks, demonstrating the sophisticated decision-making crucial for survival in urban environments where humans act as both resource providers and potential threats.

Mating Status Does Not Alter Sexual Receptivity in Females of the Harvestman Leiobunum limbatum

Pavol Prokop, Juraj Litavský, Adrián Purkart, Jozef Balcerčík — Fri, 08 May 2026 22:59:51 -0700

How do Leiobunum limbatum females respond to multiple males? We found that females readily accepted two males in close succession, apparently without male retaliation, probably because males provide nuptial gifts.

ABSTRACT

Sexual conflict arises when male and female mating optima diverge. Males of certain harvestman species frequently harass females to gain additional matings, while females strongly resist mating attempts, which could be costly for them. We hypothesize that sexual conflict is attenuated in harvestman species where males offer nuptial gifts to females. Using Leiobunum limbatum Koch, 1861, a species where males possess an ancestral, sacculate penis and offer nuptial gifts to the female during copulation, we examined sexual receptivity and copulation frequency of females allowed to mate sequentially with two different males. Females copulated with males repeatedly, and their sexual receptivity was not impaired by mating order. Female physical condition positively correlated with copulation frequency, likely because of their heightened attractiveness to males. Unexpectedly, male size correlated negatively with copulation frequency, suggesting an advantage of being small in species with scramble competition. The intensity of sexual coercion in L. limbatum seems to be lower than in other species, particularly those lacking nuptial feeding.

Cover Picture and Issue Information

Fri, 08 May 2026 05:53:21 -0700

Front Cover

A juvenile nursery web spider, Dolomedes minor, the subject of a recent study showing that males delay courtship when encountering previously mated females. Photo by Bastien Clémot.

Impact of Female Mating Status on Male Courtship Behaviour in a Sexually Cannibalistic New Zealand Fishing Spider

Bastien E. Clémot, Simon J. Connolly, Christina J. Painting — Fri, 08 May 2026 05:53:21 -0700

Scoring of male courtship behaviour in Dolomedes minor revealed no effect of female mating status on courtship duration or sequence structure, but males delayed the initiation of courtship when encountering previously mated females.

ABSTRACT

The evolution of male courtship rituals has traditionally been attributed to female mate selection, but may also hinge on male investment strategies in sexually cannibalistic species. In many spiders, males perform energetically costly courtship rituals to increase acceptance by females and minimise the risk of sexual cannibalism. However, due to sperm competition, males may invest less energy when courting already mated females, therefore driving evolutionary trade-offs between the risks of sexual cannibalism and energetic loss. Here, we investigated how female mating status influences male courtship investment in the New Zealand nurseryweb (fishing) spider, Dolomedes minor. Using laboratory experiments, we compared male courtship responses toward unmated and previously mated females. Contrary to expectations, we found that female mating status did not significantly affect male courtship duration or sequence structure, but that its primary effect was an increased latency to initiate courtship. This delayed initiation may indicate that males are expressing pre-copulatory choosiness in the face of potentially irreversible mating costs, such as genital mutilation, hesitating to commit to courtship with previously mated females rather than reducing investment once courtship has begun. Our observations also provide the first detailed ethogram and network of Dolomedes male courtship, highlighting the importance of vibrational and visual signals. These results provide a foundation for exploring additional communication modalities, such as chemical and tactile signals, and highlight the need to consider the limitations of laboratory setups when extrapolating findings to natural conditions.

Cryptic Male Choice in a Cellar Spider: Evidence of Strategic Sperm Allocation

Chad D. Hoefler, Ripken S. Wellikson — Fri, 08 May 2026 05:53:21 -0700

Male Pholcus phalangioides appear to preferentially allocate reproductive resources to large, highly fecund females, resulting in reduced offspring production in subsequent matings with medium females. Males that initially mate with large females produce fewer offspring when later paired with medium-sized females, indicating a reproductive trade-off consistent with sperm limitation and strategic ejaculate allocation. Offspring survival does not differ across mating sequences, suggesting that these effects reflect variation in sperm quantity rather than quality.

ABSTRACT

Sexual selection theory traditionally emphasizes female mate choice, yet an expanding body of research highlights the prevalence and evolutionary importance of male mate selectivity. In species where ejaculate production is energetically costly, males may exhibit cryptic mate choice by modulating pericopulatory or postcopulatory investment in response to female quality. Here, we tested for cryptic male mate choice in the long-bodied cellar spider Pholcus phalangioides, a species in which males and females mate multiply and males repeatedly induct their pedipalps with sperm throughout their adulthoods. We mated virgin males with either large or small virgin females, then remated the same males with medium-sized virgin females after a recovery period. Offspring production from medium females served as a correlate for ejaculate investment. As predicted, males that first mated with large females had reduced reproductive success in subsequent matings than males whose initial mates were small, indicating a trade-off in ejaculate allocation. However, offspring survival did not differ between groups, suggesting that sperm quantity rather than quality was affected. Although alternative explanations for our results cannot be dismissed and should be considered for future studies, our results are consistent with the hypothesis that P. phalangioides males strategically allocate reproductive resources in response to female phenotype and face sperm limitation under repeated mating. Our findings provide evidence of cryptic male choice in spiders and underscore the fitness consequences of strategic ejaculate allocation in systems lacking paternal investment.

Mechanisms of Body Alignment in a Diurnal Songbird Migrant

Christina Spiliopoulou, Giuseppe Bianco, Mihaela Ilieva, Susanne Åkesson — Fri, 08 May 2026 05:53:21 -0700

The graphical abstract illustrates the body alignment mechanism of a diurnal songbird migrant, the dunnock (Prunella modularis). Dunnocks consistently expressed an angular body alignment, with inter-individual variation at the level of the population. The preferred body alignment of individuals was selected at sunset and retained until sunrise, suggesting possible implications for compass calibration.

ABSTRACT

Animals align their body in relation to different environmental cues, including spontaneous directional responses relative to the geomagnetic field known as magnetic body alignment. The biological significance of this behavior, however, remains undetermined for most taxa. In previous studies, migratory songbirds aligned their body with the cardinal directions of the geomagnetic field and their migratory direction at different times of day. To explore the mechanisms of the alignment behavior in songbirds, we studied a diurnal migrant, the dunnock (Prunella modularis) in captivity. We captured juvenile dunnocks at stopover sites during autumn migration and assigned them to three experiments performed under controlled photic and magnetic conditions in cylindrical cages, each fitted with a circular perch enabling birds to select resting positions freely. We repeatedly measured the alignment of individual birds as the directional body orientation during rest, before and after a prolonged period of rest at sunset and sunrise on each experimental night. Several alternative orientation cues were considered to investigate the alignment of the population. Our results revealed that individuals performed angular body alignment with high consistency; however, a preferred direction was not expressed on a population level. Furthermore, the alignment position of each individual was retained throughout the resting period. These findings support the prediction that body alignment is individually selected and may be involved in compass calibration.

Observer Identity and Safety Clothing Effects on Songbird Foraging Rates

Zaharia A. Selman, Todd M. Freeberg — Fri, 08 May 2026 05:53:21 -0700

Influence of individual observer (T vs Z) and safety clothing vs camouflage clothing on seed-taking rates of songbirds from mixed-species flocks. Relative to a pre-stimulus baseline period, birds took relatively more seeds when observer T wore a camouflage vest compared to a safety vest and took relatively more seeds in the camouflage vest condition when T as opposed to Z was the observer.

ABSTRACT

Observer effects occur when the presence of human observers alters animal behavior and have been widely documented in several species. A recent study found observer distance and identity effects on foraging of mixed-species flocks of Carolina chickadees (Poecile carolinensis), tufted titmice (Baeolophus bicolor), and white-breasted nuthatches (Sitta carolinensis). We extended these observer effect studies by assessing potential effects of clothing recommended for researcher field safety. We used a within-subjects design; birds' seed-taking rates were compared when observers wore neon safety clothing versus camouflage clothing, in addition to a between-subjects manipulation of observer identity. Our results indicated a significant interaction between observer identity and observer clothing. This study highlights the need to balance field researcher safety with high-visibility clothing while minimizing detectability and altered behavioral responses in focal animal species.

Behavioral Responses of Two Common Woodland Salamanders to Novel Urban Stimuli

Amy Q. Friemoth, Brendan E. Enochs, Maggie M. Hantak — Fri, 08 May 2026 05:53:21 -0700

We examined behavioral responses of the Eastern Red-backed Salamander (Plethodon cinereus) and Northern Ravine Salamander (P. electromorphus) to novel urban stimuli. The Northern Ravine Salamander exhibited increased thigmotaxis in the presence of concrete pavers simulating roads and walkways. Both species showed negative behavioral responses to anthropogenic debris, including plastic bottles, soda cans, and styrofoam cups.

ABSTRACT

Human-modified landscapes introduce novel and challenging environments that can drive rapid shifts in species behavior. Woodland salamanders (genus Plethodon) represent a key group to investigate the effects of human disturbance as they play critical roles in forest ecosystem function yet are highly sensitive to environmental change. Here, we examined behavioral responses of two closely related species, the Eastern Red-Backed Salamander (Plethodon cinereus) and the Northern Ravine Salamander (Plethodon electromorphus), to urban environmental features. Specifically, we tested salamander boldness toward concrete substrates (mimicking roads and walkways) and neophobic responses to common anthropogenic litter items that can be found in forest patches near urban areas. We predicted both species would avoid these novel features, but that P. cinereus would be more bold given its previously documented territorial and aggressive tendencies. We quantified three exploratory behaviors: time spent moving in the open, hiding, and thigmotaxis (wall-hugging behavior) but found evidence that only P. electromorphus increased thigmotaxis on the novel substrate. Both species exhibited neophobic responses to anthropogenic litter objects. Our results suggest that these novel urban features can alter the typical behaviors of these common salamander species. Future work should assess whether such avoidance behaviors reduce opportunities for dispersal, foraging, or mating, which may influence population persistence in urbanized landscapes.

Social Drivers of Vocal Flexibility in Female Baboons

Yaëlle Bouquet, Eloïse C. Déaux, Jessica M. Rothman, Klaus Zuberbühler — Fri, 08 May 2026 05:53:21 -0700

Female olive baboons selectively grunt when encountering females with dependent offspring. Grunting likelihood depends on rank differences and the strength of their social bond. This study adds to the evidence that nonhuman primates have evolved to use structurally-inflexible vocalisations in population and context-flexible ways. Drawing credit: Guillaume Simmen.

ABSTRACT

Many social animals produce signals during close encounters but, across species, there is considerable structural and functional variation, presumably driven by social and ecological factors. In this study, we explored how wild female olive baboons in Kibale National Park, Uganda, used grunts during encounters. We found that females directed their grunts selectively towards females with dependent offspring, while taking into account rank differences and, to a lesser extent, friendship. Specifically, females were more likely to grunt towards higher-ranking and weakly-bonded mothers than other females. Unlike Guinea baboons, chacma baboons and olive baboons from central Kenya, however, Ugandan olive baboons appeared not to use grunts to reassure subordinates but to appease the riskiest partner: a higher-ranking female with a young dependent offspring. Our data suggest that baboons have evolved the ability to use part of their vocal repertoire in population-specific, socially flexible ways. We tentatively propose that these population differences relate to variations in aggression rates, social structure and/or ecological variables.

Born to be Bold? Personality Traits and Reproductive Performance in Magellanic Penguins (Spheniscus magellanicus)

Fri, 08 May 2026 05:53:21 -0700

Boldness, measured through a novel object test during incubation and chick-rearing, was repeatable across breeding stages in both male and female Magellanic penguins. However, increased boldness in males was associated with lower reproductive success, as bolder males fledged fewer chicks. These findings suggest that consistent behavioural differences may have fitness consequences.

ABSTRACT

Personality differences in animals are defined as consistent behavioral variation among individuals and are known to influence fitness. However, the mechanisms by which personality traits affect fitness remain largely underexplored. In this study, we assessed intra-annual boldness in Magellanic penguins (Spheniscus magellanicus) from a breeding colony on Isla Quiroga, Argentina, using a novel object test during incubation and chick-rearing. We estimated its repeatability, examined whether boldness correlated with reproductive performance, and explored how this relationship varied across years with differing resource availability and environmental conditions. Boldness remained consistent over the breeding season, and we found a negative association between male boldness and reproductive success, as bolder males fledged fewer chicks. In addition, although boldness was not associated with mate choice, pairs with similar boldness exhibited intermediate reproductive success (approximately one fledgling from two eggs). Overall, our findings indicate that variation in boldness behavior may play a role in shaping reproductive success in this species.

Spontaneous Rhythmic and Tool‐Assisted Drumming Across Variable Tempo and Technique in a Captive Chimpanzee

James Brooks, Vesta Eleuteri, Jelle van der Werff, Shinya Yamamoto — Wed, 06 May 2026 21:16:00 -0700

A captive chimpanzee named Toon performed an unusual long-lasting drumming session using different implements (e.g., limbs and tools) and techniques (e.g., drumstick-on-drum). He drummed faster with limbs than with tools and during the climax than the introduction of his pant-hoot displays. Toon flexibly drummed with isochronous (regular, metronome-like) rhythm across different implements, techniques, and tempi. He also showed “play face” when using faster and less variable rhythms.

ABSTRACT

Rhythmic drumming on percussive instruments is a common element of music across human cultures. Chimpanzees drum on the buttress roots of trees and on man-made objects, and often combine their drumming with long-distance pant-hoot vocalizations. Previous studies have suggested that chimpanzees select drumming substrates for their acoustic properties and that chimpanzee drumming shares core elements of human musicality (e.g., non-random timing, isochronous, metronome-like rhythm, and de-contextualized production in captivity). But to what extent can chimpanzees flexibly control their drumming rhythm across percussive media and techniques? Here, we report on a long-lasting drumming session by a captive chimpanzee named Toon, which was performed across multiple pant-hoot displays. Toon employed diverse action forms, including drumstick-on-drum tool-composite use. We find flexible (isochronous) rhythm production across drumming implements, techniques, and tempi. Further, we describe tool-composite transport and reuse, selectivity of percussive acoustic properties associated with different vocal elements, and variable use of the facial expression “play face” associated with faster and less variable rhythms, potentially indicating intrinsic enjoyment of such rhythms. Together, these findings provide evidence for key elements of human musicality in Toon's drumming, supporting the hypothesis of shared evolutionary roots of human and chimpanzee drumming.

The Effect of Heterospecific Song and Anthropogenic Sound on the Development of Life History Traits in a Field Cricket

Troy A. Bowers, Susan N. Gershman — Tue, 28 Apr 2026 00:00:00 -0700

We raised fall field crickets in acoustic environments of silence, their own song, traffic noise, or the song of the recently introduced Japanese burrowing cricket and measured development, size, and adult survival. We found that crickets reared with burrowing cricket song developed more quickly than crickets reared in silence. Japanese burrowing cricket song may represent a new, exaggerated signal that causes a stronger response than the song of their own species.

ABSTRACT

Juvenile crickets use sound cues from conspecifics to plastically develop adaptive adult traits. Human-induced rapid environmental change, including anthropogenic sound and introduced species, can cause a mismatch between juvenile and adult environments, resulting in maladaptive phenotypic plasticity. To determine the effects of traffic sound and introduced Velarifictorus micado song on Gryllus pennsylvanicus field cricket development, we raised G. pennsylvanicus crickets in silence, conspecific song, traffic noise, or heterospecific song and measured development time, body size, and lifespan. We did not find an effect of conspecific song or traffic sound on any traits. However, individuals reared with heterospecific song developed more quickly than individuals reared in silence. Rapid development would be beneficial in an adult environment with many conspecifics, but plasticity in response to heterospecific song has no clear benefit. It is possible that V. micado song represents an extreme stimulus that causes G. pennsylvanicus to display potentially maladaptive phenotypic plasticity. Our results underscore the need for more research on the effects of introduced species on acoustically communicating species.

Do Continuous and Intermittent Traffic Noise Have Similar Negative Impacts on Zebra Finch Cognitive Performance?

Sun, 26 Apr 2026 23:27:07 -0700

Does the consistency of anthropogenic noise exposure affect its impact on avian cognitive performance? We tested how accurately zebra finch learned a battery of cognitive tasks under intermittent or continuous traffic noise and demonstrate differential impacts on specific types of cognitive tasks.

ABSTRACT

Anthropogenic noise pollution levels are increasing in natural communities with numerous impacts on the behavior of animals, including recent studies demonstrating that noise negatively affects cognitive performance in birds. However, there are also examples of avian species inhabiting or even thriving in urbanized habitats, suggesting that animals might overcome the challenges posed by anthropogenic noise, perhaps by habituating with repeated exposure. We examined whether zebra finches habituate to road noise when presented with continuous playback of road traffic noise versus intermittent noise playback as they learned novel foraging tasks. We hypothesized that birds exposed to continuous traffic noise during and between repeated trials would demonstrate higher cognitive performance than birds with intermittent exposure. We used a battery of foraging tasks that measured different aspects of cognition, including inhibitory control, motor learning, color association, and spatial memory. We found that birds presented with continuous noise exposure had higher performance scores in the motor learning and spatial memory tasks, but we did not observe differences between treatments for inhibitory control or color association tasks. These results suggest that birds were unable to broadly habituate to the traffic playback. Instead, habituation or reduced distraction could occur only in some cognitive domains; certain cognitive activities or modules could be more sensitive to noise-induced cognitive impairment than others, or other intrinsic factors might determine an animal's response to distracting stimuli.

Rethinking Behaviors of Free‐Ranging Asian Elephants in the Context of Human‐Altered Landscapes

Sanjeeta Sharma Pokharel, Nachiketha Sharma — Fri, 17 Apr 2026 05:12:55 -0700

Context-specific behavioral flexibility in free-ranging Asian elephants navigating human-altered landscapes.

ABSTRACT

Animals display context-specific behavioral flexibility in response to varying environmental and anthropogenic pressures. Such responses are modulated by ecological constraints, social dynamics, and temporal variation, frequently resulting in divergent strategies even among conspecifics. These changes are commonly expressed through shifts in behavioral repertoire, reflecting the plasticity required to navigate novel or altered ecosystems. Here, we highlight some of the behavioral responses of a highly social and cognitively advanced species, the Asian elephant, living in human-altered landscapes. Altered activity budgets and the emergence of context-specific behaviors observed in anthropogenic landscapes suggest that elephants actively attempt to cope with rapidly changing habitats. While such flexibility may confer short-term adaptive benefits to elephants, its long-term fitness consequences remain uncertain. These observations challenge conventional baselines of elephant behavior derived from relatively undisturbed habitats and highlight the need to redefine “normal” behavioral expression in anthropogenically altered landscapes. Comparative, context-specific behavioral analyses are therefore essential to avoid overgeneralization and to support more nuanced, evidence-based conservation strategies.

A Newly Reported Tactile Gesture for Grooming Initiation in Japanese Macaques (Macaca fuscata) at Awajishima, Japan

Yu Kaigaishi — Mon, 06 Apr 2026 23:00:00 -0700

Tapping behaviour observed in the Awajishima group of Japanese macaques. An individual touches the other's back, which functions as a signal to initiate grooming between the two.

ABSTRACT

Communicative signals such as vocalizations, facial expressions and gestures enable animals to communicate their intentions to other individuals. As one of such signals, primates often perform grooming solicitation (hereafter, solicitation), in which an individual lies in front of another or shows its body part to elicit grooming from other individuals. In a free-ranging group of Japanese macaques (Macaca fuscata) at Awajishima, Japan, another form of gesture for grooming initiation is sometimes observed, which has been unreported in this species. In this behavior, which is named ‘tapping’, an individual softly touches another individual, often followed by grooming between the two. In this study I investigated how tapping is used in this group in comparison with solicitation, especially focusing on its function and social relationships between the signalers and the receivers. In most cases, tapping was followed by grooming but no other affiliative interactions. While solicitation was used by both males and females, tapping was observed almost exclusively between adult females. Compared with solicitation, tapping was more likely to occur between less affiliative, non-kin-related dyads and more likely to be directed from the dominant to the subordinate. These results suggest that tapping functions as a tactile gesture to initiate grooming, especially with more weakly-bonded partners. Finally, social network analysis revealed that tapping was preliminarily used among the highest ranked females. Tapping might be a cultural behavior of the Awajishima group, potentially related to specifically high social tolerance of this group.

Ripple Effects: Social Turmoil Following Infant Kidnapping Attempts in Wild Geladas

Thu, 02 Apr 2026 21:01:04 -0700

Graphical abstract illustrating the social consequences of infant kidnapping in wild geladas (Theropithecus gelada). The study monitors a 28-day period divided into a 14-day pre-kidnapping phase and a 14-day post-kidnapping phase.

ABSTRACT

Infant kidnapping is an extreme social disruption reported in some primate species, yet its consequences on social group dynamics remain poorly understood. We document a rare case of repeated attempts of infant kidnapping after handling in a wild gelada one-male unit and quantify its social impact using Social Network Analysis. The kidnapper, a subadult female frequently aided by another female supporter, repeatedly removed a newborn from its mother without caregiving attempts, inducing stress responses in both mother and infant. Following the kidnapping episodes, grooming networks became denser, more reciprocal and showed a higher tendency to form closed triads, with a marked increase in affiliative exchanges between the kidnapper and her supporter. Agonistic interactions also increased in frequency and involved more individuals, indicating a broad destabilizing effect on group-level relationships. Our results indicate that, despite being an anecdotal case, this rare naturalistic observation provides a unique opportunity to understand the immediate factors leading to kidnapping and how such an extreme perturbation can trigger rapid, measurable reorganization in a wild primate society.

Male Octopus Avoid Using Hectocotylized Arm Under Situations With Unpredictable Risks

Keijiro Haruki, Yuta Yamate, Takeshi Takegaki — Fri, 27 Mar 2026 09:45:34 -0700

Octopus males are thought to protect their right third arm, an essential arm for reproduction (hectocotylus), but it has not been verified. We examined male Octopus parvus' arm loss and arm use in aquarium experiments. Fewer males lost R3 arm than females. In the experiment of touching a novel object, males never used R3 arm, and in the experiment of exploring prey in a hole, males explored with arms other than R3 longer than females before inserting R3 arm.

ABSTRACT

Anti-predator behaviours are generally considered as those that prevent death from predation. However, even if prey animals survive, they might suffer sub-lethal injuries. Although it is predicted that prey would minimise injury by protecting vital body parts, such defensive strategies have not been widely recognised in previous studies. While cephalopods frequently lose arms, males rarely lose their hectocotylus, an essential arm for reproduction. This is considered to be a result of the male's protection of the hectocotylus, but it has not been verified. This study investigated arm loss in Octopus parvus in the wild and tested whether males protect their hectocotylus (right third arm, R3) by avoiding its use during tasks with unpredictable truncation risk. Arm loss was observed in 78% of wild-caught individuals, and males lost R3 arm significantly less often than females. In Experiment 1, males did not use their hectocotylus at all to physically explore a novel object (fishing sinker), while females used R3 arm just as frequent as her other arms. In Experiment 2, the number of individuals explored prey in a hole using R3 arm did not differed significantly between sexes, but males explored the hole with arms other than R3 arm longer than females before inserting R3 arm. These results suggest that O. parvus males avoid risk more for the hectocotylus than for the other arms, i.e., hectocotylus arm protection. Males did not always protect their hectocotylus, and they sometimes inserted their hectocotylus after exploring the hole with other arms in Experiment 2. Males might suffer behavioural disadvantages by persistently guarding their hectocotylus.