Alarm calls elicit predator-specific physiological responses

Glucocorticoids regulate glucose concentrations and responses to unpredictable events, while also modulating cognition. Juvenile Belding''s ground squirrels (Urocitellus beldingi) learn to respond to whistle and trill alarm calls, warning of aerial and terrestrial predators, respectively, shortly after emerging from natal burrows at one month of age. Alarm calls can cause physiological reactions and arousal, and this arousal, coupled with watching adult responses, might help juveniles learn associations between calls and behavioural responses. I studied whether young show differential cortisol responses to alarm and non-alarm calls, using playbacks of U. beldingi whistles, trills, squeals (a conspecific control vocalization) and silent controls. Trills elicited very high cortisol responses, and, using an individual''s response to the silent control as baseline, only their response to a trill was significantly higher than baseline. This cortisol increase would provide glucose for extended vigilance and escape efforts, which is appropriate for evading terrestrial predators which hunt for long periods. Although whistles do not elicit a cortisol response, previous research has shown that they do result in bradycardia, which enhances attention and information processing. This is a novel demonstration of two physiological responses to two alarm calls, each appropriate to the threats represented by the calls.     

Songs differing in consistency elicit differential aggressive response in territorial birds

Acoustic signals during intrasexual interactions may help receivers to establish the cost and benefits of engaging in a confrontation versus avoiding the cost of escalation. Although birdsong repertoires have been previously suggested as providing information during agonistic encounters, the cost (time/neural resources) of assessing large repertoires may decrease the efficiency of the signal for mutual assessment. Acoustic-structural features may, therefore, be used to enable a fast and accurate assessment during this kind of encounters. Recently, it has been suggested that the consistency of songs may play a key role during intrasexual interactions in bird species. Using a playback experiment in a colour-ringed great tit population, we tested the hypothesis that songs differing in consistency may elicit a differential response, indicating that the signal is salient for the receivers. Great tit males clearly responded more aggressively towards highly consistent songs. Our findings, together with previous evidence of increased song consistency with age in the great tit, suggest that song consistency provides information on experience or dominance in this species, and this phenomenon may be more widespread than currently acknowledged.     

The role of synchronized swimming as affiliative and anti-predatory behavior in long-finned pilot whales

Synchronized swimming in cetaceans has been hypothesized to play a role in affiliative processes as well as anti-predatory responses. We compared observed variation in synchronized swimming at two research sites in relation to disturbance exposure to test these two hypotheses. This study describes and quantifies pair synchronization in long-finned pilot whales at the Strait of Gibraltar, Spain and Cape Breton, Canada. Synchronization differed depending on the behavioral state and the response is different in the two sites leading to the conclusion that environment can shape the occurrence and magnitude of certain behaviors. We also analyzed intra-population variations in synchronization among 4 social units of Pilot whales in the Strait of Gibraltar and the results of this study confirmed the affiliative role of synchronization and highlighted an influence of disturbance on synchronization. We can conclude that synchronization is a common behavior in long-finned pilot whales that allow for close proximity and rapid coordinated response of individuals, with the multiple functions of showing affiliation and reacting to disturbance.     

Female bonobos use copulation calls as social signals

During mating events, females of many primate species produce loud and distinct vocalizations known as 'copulation calls'. The adaptive significance of these signals is considered to be in promoting the caller's direct reproductive success. Here, we investigated copulation calling in bonobos (Pan paniscus), a species in which females produce these vocalizations during sexual interactions with partners of both sexes. Females were more likely to call when mating with males than with females. We also observed a positive relationship between the likelihood of calling and partner rank, regardless of partner sex. Sexual activity generally increased with swelling size (an indicator of reproductive state) and, during their peak swelling, females called more with male than with female partners. Female bonobos are unusual among the non-human primates in terms of their heightened socio-sexuality. Our results suggest that in this species, copulation calls have undergone an evolutionary transition from a purely reproductive to a more general social function, reflecting the intrinsic evolutionary links between vocal behaviour and social cognition.     

Differences in the nestling begging calls of hosts and host-races of the common cuckoo, Cuculus canorus

We compared nestling begging calls of four hosts (reed warbler, Acrocephalus scirpaceus; great reed warbler, A. arundinaceus; dunnock, Prunella modularis; and meadow pipit, Anthus pratensis) and the respective host-races of the common cuckoo. Note structure varied between host species, but not between cuckoo host-races, so cuckoos did not vary their call note structure to match that of their hosts' chicks. Call rate increased with age, but there were marked differences between both host species and cuckoo host-races. Dunnock-cuckoos called more rapidly than reed warbler-cuckoos despite growing at the same rate. We suggest this difference reflects how cuckoos tune into the way these host species respond to begging signals from their own young, because dunnock chicks called much more rapidly than reed warbler chicks. Great reed warbler-cuckoos called at a lower rate than reed warbler-cuckoos when young, but at a greater rate when older than 8 days. This could also result from the cuckoo chicks tuning into differences in the way these hosts respond to begging signals. However, great reed warbler-cuckoos grew at a faster rate than the other cuckoo host-races, so they may also call faster to demand higher provisioning rates from this larger host. To test these hypotheses critically, data are needed on how the different host species integrate visual and vocal begging signals from their own broods. We discuss how differences in cuckoo begging might develop, given that cuckoo host-races are restricted to female cuckoo lineages. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.      

Optimal strategies and complexity: A theoretical analysis of the anti-predatory behavior of the hare

Predator—prey relationships involving rabbits and hares are widely studied at a long-term population level, while the short-term ethological interactions between one predator and one prey are less well documented. We use a physiologically-based model of hare behavior, developed in the framework of artificial intelligence studies, to analyse its sophisticated anti-predatory behavior. The hares use to stand to the fox in order to inform it that its potential prey is alerted. The behavior of the hare is characterized by specific standing and flushing distances. We show that both hare survival probability and body condition depend on habitat cover, as well as on the ability of the predator to approach—undetected—a prey. We study two anti-predatory strategies, one based on the maximization of the survival probability and the other on the maximization of the body conditions of the hare. Despite the fact that the two strategies are not independent, they are characterized by quite different behavioral patterns. Field estimates of flushing and standing distances are consistent with survival maximization. There exists an optimal anti-predatory strategy, characterized by a flushing distance of 20 m and a standing distance of 30 m, which is optimal in a large set of environmental conditions with a sharp fitness advantage with respect to suboptimal strategies. These results improve our understanding of the anti-predatory behavior of the hare and lend credibility to the optimality approach in the behavioral analysis, showing that even for complex organisms, characterized by a large network of internal constraints and feedback, it is possible to identify simple optimal strategies with a large potential for selection.     

Female choice for genetic complementarity in birds: a review

Data from avian species have played a prominent role in developing and testing theories of female mate choice. One of the most prominent models of sexual selection, the "good genes" model, emphasizes the indirect benefits of female preferences for male ornaments as indicators of a potential sire's additive genetic quality. However, there is growing interest in non-additive sources of genetic quality and mate choice models for self-referential disassortative mating based on optimal levels of genetic dissimilarity. We reviewed the empirical evidence for genetic-complementarity-based female mate choice among birds. We found the evidence for such choice is mixed but in general against the genetic complementarity hypothesis. The lack of evidence for genetic complementarity in many birds may be due to an inability to make the fine distinctions among potential mates based on genes, possibly due to the comparative anosmatic nature of avian sensory system. For some species however there is compelling evidence for genetic complementarity as a criterion used in female mate choice. Understanding the ubiquity of female mate choice based on genetic complementarity and the variation in this source of female preference among and within species remains a challenge.     

Female preference for fast-rate, high-pitched calls in Hermann's tortoises Testudo hermanni

The courtship and mounting behavior of promiscuous tortoisesis based on a multiple signaling system that includes visual,olfactory, tactile, and acoustic signals. Vocalizations relatedto mounting seem to be particularly intriguing because tortoisesvocalize mainly at this time. Vocalizations and courtship behaviormight be costly for males, and if these costs increase differentiallyfor different males, then the potential exists for vocalizationsand displays to reveal male individual quality on which femalescould base their mate choice. In the present study, by usingindividuals breeding in seminatural enclosures, we experimentallyinvestigated whether the mounting call of male Hermann's tortoises(Testudo hermanni) represents a relevant stimulus to both malesand females. We also looked for potential preference towarddifferent acoustic stimuli in order to determine which callfeatures, if any, played a role in attracting potential partnersor deterring rivals. Females were sensitive to call playback,whereas males apparently paid little attention to playback.In addition, females showed a significant preference towardhigh-pitched calls emitted at high rate. Also, females exhibiteda strong tendency toward short-duration calls. Because callrate is related to hematocrit in Hermann's tortoise males, byresponding to fast-rate calls females are also choosing high-qualitypartners as sires of their offspring. This is the first studyin which an attractive function of tortoise vocalizations hasbeen documented.     

Abnormal behavior in caged birds kept as pets

There are a limited number of studies dealing with abnormal behavior in caged birds kept as pets. However, these studies demonstrate the presence of abnormal behavior in both songbirds and parrots. Ethological studies on these birds, as well as studies on domestic and zoo birds, indicate that inappropriate rearing and housing conditions may lead to behavioral abnormalities. Together these data indicate that behavioral abnormalities occur among both wild-caught and domesticated pet birds. The severity and magnitude of these abnormalities is probably underestimated, and there is a need for systematic studies on the nature, origin, variability, species-specificity, and reversibility of behavioral problems in pet birds. Abnormal behavior in caged birds may to some extent be prevented and reduced by environmental enrichment. However, most enrichment studies are anecdotal and not based on a thorough analysis of the behavioral abnormalities, which may lead to measures resulting in a reduction of symptoms rather than the underlying causes. Although it is likely that several of these problems could be reduced by modifying rearing and housing conditions, the current insights into the causal mechanisms underlying abnormal behavior of domesticated and wild-caught pet birds are limited, as are the insights into the possibilities of preventing or curing abnormal behavior.     

Referential calls signal predator behavior in a group-living bird species

Predation is a powerful agent of natural selection, driving the evolution of antipredator calls [1]. These calls have been shown to communicate predator category [2-4] and/or predator distance to conspecifics [5-7]. However, the risk posed by predators depends also on predator behavior [8], and the ability of prey to communicate predator behavior to conspecifics would be a selective advantage reducing their predation risk. I tested this idea in Siberian jays (Perisoreus infaustus), a group-living bird species. Predation by hawks, and to a lesser extent by owls, is substantial and the sole cause of mortality in adult jays [9]. By using field data and predator-exposure experiments, I show here that jays used antipredator calls for hawks depending on predator behavior. A playback experiment demonstrated that these prey-to-prey calls were specific to hawk behavior (perch, prey search, attack) and elicited distinct, situation-specific escape responses. This is the first study to demonstrate that prey signals convey information about predator behavior to conspecifics. Given that antipredator calls in jays aim at protecting kin group members [10, 11], consequently lowering their mortality [9], kin-selected benefits could be an important factor for the evolution of predator-behavior-specific antipredator calls in such systems.     

A host-race of the cuckoo Cuculus canorus with nestlings attuned to the parental alarm calls of the host species

The common cuckoo has several host-specific races, each with a distinctive egg that tends to match its host's eggs. Here, we show that the host-race specializing on reed warblers also has a host-specific nestling adaptation. In playback experiments, the nestling cuckoos responded specifically to the reed warbler's distinctive 'churr' alarm (given when a predator is near the nest), by reducing begging calls (likely to betray their location) and by displaying their orange-red gape (a preparation for defence). When reed warbler-cuckoos were cross-fostered and raised by two other regular cuckoo hosts (robins or dunnocks), they did not respond to the different alarms of these new foster-parents. Instead, they retained a specific response to reed warbler alarms but, remarkably, increased both calling and gaping. This suggests innate pre-tuning to reed warbler alarms, but with exposure necessary for development of the normal silent gaping response. By contrast, cuckoo chicks of another host-race specializing on redstarts showed no response to either redstart or reed warbler alarms. If host-races are restricted to female cuckoo lineages, then chick-tuning in reed warbler-cuckoos must be under maternal control. Alternatively, some host-races might be cryptic species, not revealed by the neutral genetic markers studied so far.     

Species-specific foraging behavior of birds in a riparian forest

In riparian forest, insectivorous birds are largely dependent on aquatic preys. However, the contribution made by aquatic preys to bird diets varies considerably among bird species. In the present study, bird foraging behaviors were observed in order to examine the relationship between bird foraging method and the variation in the contribution of aquatic preys. The great tit, the black-faced bunting, and the wren are largely dependent on aquatic preys by capturing them on the ground. Sallyers, the brown flycatcher, the pale-legged willow warbler, and the narcissus flycatcher are also largely dependent on aquatic preys and capture them mostly during flight. The narcissus flycatcher frequently utilises aquatic invertebrates dwelling on the ground. The leaf and branch gleaner, the crowned willow warbler, does not depend on aquatic prey as much. Although both the pygmy woodpecker and nuthatch are branch and trunk gleaners, the nuthatch utilises aquatic preys frequently by capturing them on the ground as well as during flight, but the pygmy woodpecker does not depend on aquatic preys. The marsh tit also does not depend on aquatic preys but carefully searches terrestrial prey that hide in the vegetation. The differential dependence on aquatic preys among species can lead to the heterogeneous distribution of birds within a riparian forest, suggesting that the indirect effect of aquatic preys on a forest ecosystem via birds can vary within a forest–stream ecotone.     

Proximate and ultimate factors explaining floating behavior in long-lived birds

Avian populations are composed of reproductive individuals coexisting in space and time with young, non-breeding conspecifics or “floaters”. Despite the fact that first breeding can be delayed for years and can exert profound effects on fitness, many aspects of the behavior, ecology and physiology of young floaters remain poorly understood. By means of combining endocrine, behavioral and life history information from a population of black kites (Milvus migrans) monitored long-term, we tested several hypotheses suggesting endocrine function as a determinant of floating status. Sexual function in non-breeding males, estimated through determination of systemic testosterone and progesterone levels, was similar to that in reproductively active conspecifics. Floating females, on the contrary, displayed an endocrine pattern of circulating estrogens and progesterone that was parallel in timing but reduced in magnitude as compared to breeders. Our results suggest that floaters are not physiologically constrained to reproduce, but the cost-benefit balance of attaining complete gonadal function is sexually dependent. While young, unmated males could increase their breeding prospects by attaining sexual maturity regardless of their social environment, natural selection would favor females relying on social cues to mature. Consistent with the sexual roles of socially monogamous species, gonadal recrudescence and testosterone production would allow unmated males to access breeding resources (e.g. through male-male competition and extra-pair fertilizations). Unmated females, on the contrary, would reduce physiological costs by means of delaying ovarian maturation until establishing pair bonds with a male providing access to breeding resources.     

Temporal and spatial variations in the behavior of shrubsteppe birds

Summary We documented patterns of activity and microhabitat use by breeding male Sage Sparrows (Amphispiza belli) and Brewer's Sparrows (Spizella breweri) in the semiarid shrubsteppe of northwestern U.S.A. to determine how their behavior varies in space and time and how these variations relate to environmental features. In analyses of several sites with multiple plots that were studied for 2–4 yr, the frequencies of activities and substrate use varied significantly with year, plot, and location. The major activities, foraging and singing, varied inversely with one another. Thus, although the general structure of the activity budgets of these species was stable (i.e. foraging and singing were always the most frequent activities), there was considerable variation in the quantitative details of their behavior in space and time. Using stepwise regression, we related these variations in behavior to variations in environmental features such as the densities of the same or other species, the number of species in the community, and coverages of the different substrate types. Few patterns emerged, and those that did were generally not in accord with our expectations. In particular, patterns of substrate use were not related to variations in coverages of those substrates. Sage Sparrows, for example, increased their use of sagebrush and grass with increasing grass coverage and with increasing densities of Sage Sparrows. Responses to both variables suggested nonlinear threshold patterns.We interpret the variations in behavior as indicating a loose coupling between behavior and proximate environmental conditions for these species. In such situations, the variability of behavior complicates attempts to test ecological hypotheses (e.g. behavioral niche partitioning) with data from a limited number of locations or years.     

Vision as a third sensory modality to elicit attack behavior in a nocturnal spider

Cupiennius salei (Ctenidae) has been extensively studied for many years and is probably the only spider that presently can be considered a model organism for neuro-ethology. The night-active spiders have been shown to predominantly rely on their excellent mechano-sensory systems for courtship and prey capture, whereas vision was assumed to play a minor role, if any, in these behavioral contexts. Using slowly moving discs presented on a computer screen it could be shown for the first time that visual stimuli alone can elicit attack behavior (abrupt approaching reactions) in these spiders as well. These observations suggest that visual information could be used by the spiders to elicit and guide predatory behavior. Attack behavior in Cupiennius salei can thus be triggered independently by three sensory modalities—substrate vibrations, airflow stimuli, and visual cues—and offers an interesting model system to study the interactions of multimodal sensory channels in complex behavior.