Competitive interactions between spotted hyenas and lions in the Etosha National Park, Namibia

Spotted hyenas are successful hunters, but they also scavenge. Their main food competitors are lions. In the Etosha National Park, Namibia hyenas are unable to prevent kleptoparasitism by lions and fail to acquire kills from lions. The reasons are the small ratio of hyenas to female and subadult lions at kills and the presence of adult male lions. Because of the hyenas’ small clan sizes and large territories they seem to be unable to recruit sufficient clan members to take over lion kills or deter lions from their own kills. In Etosha, 71% of hyena mortality was due to lions; four cubs and one adult female hyena were killed by male lions during a 1‐year study. Hyenas have evolved adaptations against lions and initiate aggressive interactions with lions without the immediate availability of food, which is termed mobbing behaviour. Etosha hyenas initiated mobbing attempts when lions were near the hyena's communal den. Possibly, Etosha hyenas mobbed lions to distract lions from the hyenas’ den and their cubs and to warn their dependent offspring to hide from lions.     

Cost of mobbing call to breeding pied flycatcher, Ficedula hypoleuca

Mobbing signals advertise the location of a stalking predatorto all prey in an area and recruit them into the inspectionaggregation. Such behavior usually causes the predator to moveto another area. However, mobbing calls could be eavesdroppedby other predators. Because the predation cost of mobbing callsis poorly known, we investigated whether the vocalizations ofthe mobbing pied flycatcher, Ficedula hypoleuca, a small holenesting passerine, increase the risk of nest predation. We usedmobbing calls of pied flycatchers to examine if they could lurepredators such as the marten, Martes martes. This predator usuallyhunts by night and may locate its mobbing prey while restingnearby during the day. Within each of 56 experimental plots,from the top of one nest-box we played back mobbing sounds ofpied flycatchers, whereas blank tapes were played from the topof another nest-box. The trials with mobbing calls were carriedout before sunset. We put pieces of recently abandoned nestsof pied flycatchers and a quail, Coturnix coturnix, egg intoeach of the nest-boxes. Nest-boxes with playbacks of mobbingcalls were depredated by martens significantly more than werenest-boxes with blank tapes. The results of the present studyindicate that repeated conspicuous mobbing calls may carry asignificant cost for birds during the breeding season.     

The nest defence by the red‐backed shrike Lanius collurio – support for the vulnerability hypothesis

The majority of altricial bird species defend their brood against predators more intensively in nestlings rather than eggs stage. Several hypotheses have been proposed to explain this difference. The majority of existing experimental studies have recorded a gradually increasing intensity of nest defence supporting the reproductive value hypothesis. We have compared nest defence in two nesting stages of the red‐backed shrike against two predators of adult birds and against two predators of nests. While the nests with nestlings were defended by parents against three out of four predators, nests with eggs were almost not defended at all. This rapid change in parent nest defence supports rather the vulnerability hypothesis, predicting that the threat to nests with nestlings increases rapidly after hatching, as they became more conspicuous due to their begging and parental provisioning. Unlike most of the species tested previously, the red‐backed shrike uses very vigorous mobbing towards predators. We suggest that the occurrence of this active mobbing (strikes, including physical contact) is a good proxy of the current threat to the nest.     

Long-lasting mobbing of the pied flycatcher increases the risk of nest predation

Mobbing behavior may provide real benefits because mobbing preyindividuals often cause a predator to leave the vicinity. However,mobbing calls of prey can attract acoustically oriented predatorsthus increasing nest predation. Therefore, a real value of mobbingas a type of adaptive behavior may depend on its duration. Inthis experimental study, we tested whether mobbing durationby the pied flycatcher Ficedula hypoleuca, a small hole-nestingpasserine, increases the risk of nest predation. From the topof one nest-box within each of 78 experimental plots, we playedback long calls of pied flycatchers, whereas recordings of shortmobbing calls were played back from the top of another nearbynest-box. The nest-boxes were arranged in pairs, and each ofthem contained a quail Coturnix coturnix egg. Long-call nest-boxeswere depredated by martens Martes martes significantly moreoften than short-call nest-boxes. This predator usually huntsby night and may eavesdrop on the calls of their mobbing preywhile resting nearby during the day. The results of the presentstudy show that long-lasting conspicuous mobbing calls may carrya significant cost for the breeding birds.     

Mobbing behaviour in a passerine community increases with prevalence in predator diet

Mobbing behaviour against predators is well documented but less is known about the factors influencing variation in behavioural response between prey species. We conducted a series of playback experiments to examine how the mobbing responses of prey species differed according to their relative risk of predation by the Eurasian Pygmy Owl Glaucidium passerinum, a predator of passerines. We found that mobbing among 22 passerine prey species was positively correlated with their prevalence in the Pygmy Owl diet. To compare mobbing behaviour between two seasons, we conducted playback experiments during spring (breeding season) and autumn (non‐breeding season). Contrary to previous studies, we found that mobbing intensity was greater during autumn than in spring. Our study shows a differential mobbing response of 22 species to the calls from one predator species and underscores the importance of considering seasonal variation in mobbing behaviour. Mobbing response differences observed among bird species strongly suggest different cooperation behaviour at the community level.     

The sight of an adult brood parasite near the nest is an insufficient cue for a honeyguide host to reject foreign eggs

Hosts of brood‐parasitic birds typically evolve anti‐parasitism defences, including mobbing of parasitic intruders at the nest and the ability to recognize and reject foreign eggs from their clutches. The Greater Honeyguide Indicator indicator is a virulent brood parasite that punctures host eggs and kills host young, and accordingly, a common host, the Little Bee‐eater Merops pusillus frequently rejects entire clutches that have been parasitized. We predicted that given the high costs of accidentally rejecting an entire clutch, and that the experimental addition of a foreign egg is insufficient to induce this defence, Bee‐eaters require the sight of an adult parasite near the nest as an additional cue for parasitism before they reject a clutch. We found that many Little Bee‐eater parents mobbed Greater Honeyguide dummies while ignoring barbet control dummies, showing that they recognized them as a threat. Surprisingly, however, neither a dummy Honeyguide nor the presence of a foreign egg, either separately or in combination, was sufficient to stimulate egg rejection.     

Can Auditory Playback Condition Predator Mobbing in Captive-reared <Emphasis Type="Italic">Saguinus oedipus</Emphasis>?

Captive reintroductions often suffer high mortality, with predation as one source. Many species learn about predators; thus training captive-born animals to recognize predators may increase survivorship. We adapted variants of methods developed for birds to attempt to condition monkeys to mob a predator. Captive-reared cotton-top tamarins (Saguinus oedipus) did not differentiate between a snake and a rat, confirming previous research that naïve cotton-top tamarins do not fear snakes. Tamarins then viewed a living snake during playback of mobbing calls. In posttests, tamarins did not mob the snake. We then eliminated the pretest to avoid potential habituation and placed a stillborn tamarin with the snake in an attempt to heighten arousal. In posttests, tamarins again did not mob the snake, although they did increase their rates of calls, indicating mild arousal. Overall, none of 8 groups of cotton-top tamarins learned to mob a predator. Potential reasons for failure include conditioning multiple subjects at once and the lack of an experienced demonstrator. Observing a demonstrator was not necessary for birds to acquire mobbing, but may be necessary for tamarins.     

Condition explains individual variation in mobbing behavior

During mobbing, individuals approach predators with the apparent aim of reducing the risk of predation. The intensity of mobbing may depend on the costs and benefits of this behavior, which likely vary among individuals and between different social contexts. We studied whether Dark‐eyed junco male mobbing behavior is related to social environment, individual condition, and age during experimentally induced mobbing events. Based on risk‐taking theory, we predicted that individuals with high residual reproductive value—younger individuals and those in better condition—would show weaker mobbing behavior. We also expected to see weaker mobbing when the total number of individuals in the mobbing assemblage was small. All subjects were caught to assess condition and age. Focal males were then attracted to simulated mobbing events using heterospecific alarm calls. Social environment did not explain individual variation in mobbing behavior in focal juncos. Community‐wise, the relationship between the closest approach and group size was not significantly different from chance. Junco males in better condition approached the predator less closely and were less likely to give alarm calls. Age did not explain variation in mobbing. Both the mean approach and probability of giving alarm calls by junco males were repeatable, in contrast to the size and composition of mobbing assemblages in junco territories, which were inconsistent. Our results show that variation in mobbing can be linked to individual state, which likely affects the costs and benefits of mobbing.     

Antipredator behavior in lemurs: Evidence of an extinct eagle on Madagascar or something else?

Goodman (1994) related the antipredator response exhibited by two species of lemurs from southwestern Madagascar against extant birds of prey to the predatory efforts of an extinct eagle, inhabiting the same region about 4000 years ago. He argued that today’s smaller raptors, hunting young individuals perhaps only occasionally, represent marginal danger to lemurs. Nevertheless,their activity would be sufficient to impose a continuous reinforcement to a strong antipredator response. I question such an interpretation and instead suggest that extant birds of prey may indeed represent a strong threat to lemurs and that the same might not have been necessarily true for the extinct eagle. In addition, I propose four optional hypotheses, all of which encompass a marginal role for the extinct eagle.     

Mutualism,reciprocity, or kin selection? Cooperative rescue of a conspecific from a boa in a nocturnal solitary forager the gray mouse lemur

Predator mobbing is a widespread phenomenon in many taxa but the evolution of cooperative mobbing as an adaptive behavior is still subject to debate. Here, we report evidence for cooperative predator defense in a nocturnal solitarily foraging primate, the gray mouse lemur (Microcebus murinus). Several mouse lemurs mobbed a snake that held a non-related male conspecific until he could escape. Evolutionary hypotheses to explain cooperative mobbing include (1) by-product mutualism, when individuals defend others in the process of defending themselves; (2) reciprocity, where animals achieve a higher fitness when helping each other than when they do not cooperate; and (3) kin selection where animals help each other only if they share genes by common descent. Owing to the solitary activity of this species, reciprocity seems to be least likely to explain our observations. By-product mutualism cannot be ruled out entirely but, if costs of snake mobbing are relatively low, the available detailed socio-genetic information indicates that kin selection, rather than any of the other proposed mechanisms, is the primary evolutionary force behind the observed cooperative rescue.     

The Effects of Human Age,Group Composition,and Behavior on the Likelihood of Being Injured by Attacking Pumas

ABSTRACT

Documentation from the years 1890 to 2000 of 185 instances of pumas (Puma concolor) attacking humans in the United States and Canada has provided statistical evidence that pumas are less likely to kill or injure humans in certain circumstances. We identified incidents of fatal attacks, severe injuries, light injuries, and no injuries as a function of human age class, group size, body posture, and conspicuous action, such as noise making, running, or shooting. Ordinal multinomial regression revealed that age class (< 13 years old vs. older) was not a statistically reliable predictor of attack severity. This statistical method also revealed that there was no reliable association between the number of individuals present during the attack and attack severity. Nevertheless, examination of specific attack outcomes indicated that the likelihood of escaping injury increased when two or more people were present. The speed that individuals moved during the attack did not predict attack severity, but it was apparent that the lowest likelihood of escaping injury (26%) and greatest frequency of severe injuries (43%) occurred when individuals remained stationary. In contrast, half of the individuals who ran when they were attacked escaped injury, whereas running was associated with only a small increase in the frequency of fatal attacks (28%), compared with remaining stationary (23%). Evidence that half of the individuals who ran escaped injury suggests that pumas are assessing immobility in humans as they might with other prey, using it as an index of prey inattention or disablement and hence greater vulnerability.     

Functional traits determine heterospecific use of risk‐related social information in forest birds of tropical South‐East Asia

In birds and mammals, mobbing calls constitute an important form of social information that can attract numerous sympatric species to localized mobbing aggregations. While such a response is thought to reduce the future predation risk for responding species, there is surprisingly little empirical evidence to support this hypothesis. One way to test the link between predation risk reduction and mobbing attraction involves testing the relationship between species’ attraction to mobbing calls and the functional traits that define their vulnerability to predation risk. Two important traits known to influence prey vulnerability include relative prey‐to‐predator body size ratio and the overlap in space use between predator and prey; in combination, these measures strongly influence prey accessibility, and therefore their vulnerability, to predators. Here, we combine community surveys with behavioral experiments of a diverse bird assemblage in the lowland rainforest of Sumatra to test whether the functional traits of body mass (representing body size) and foraging height (representing space use) can predict species’ attraction to heterospecific mobbing calls. At four forest sites along a gradient of forest degradation, we characterized the resident bird communities using point count and mist‐netting surveys, and determined the species groups attracted to standardized playbacks of mobbing calls produced by five resident bird species of roughly similar body size and foraging height. We found that (1) a large, diverse subcommunity of bird species was attracted to the mobbing calls and (2) responding species (especially the most vigorous respondents) tended to be (a) small (b) mid‐storey foragers (c) with similar trait values as the species producing the mobbing calls. Our findings from the relatively lesser known bird assemblages of tropical Asia add to the growing evidence for the ubiquity of heterospecific information networks in animal communities, and provide empirical support for the long‐standing hypothesis that predation risk reduction is a major benefit of mobbing information networks.     

Behavioral responses to conspecific mobbing calls are predator‐specific in great tits (Parus major)

When facing a predator, animals need to perform an appropriate antipredator behavior such as escaping or mobbing to prevent predation. Many bird species exhibit distinct mobbing behaviors and vocalizations once a predator has been detected. In some species, mobbing calls transmit information about predator type, size, and threat, which can be assessed by conspecifics. We recently found that great tits (Parus major) produce longer D calls with more elements and longer intervals between elements when confronted with a sparrowhawk, a high‐threat predator, in comparison to calls produced in front of a less‐threatening tawny owl. In the present study, we conducted a playback experiment to investigate if these differences in mobbing calls elicit different behavioral responses in adult great tits. We found tits to have a longer latency time and to keep a greater distance to the speaker when sparrowhawk mobbing calls were broadcast. This suggests that tits are capable of decoding information about predator threat in conspecific mobbing calls. We further found a tendency for males to approach faster and closer than females, which indicates that males are willing to take higher risks in a mobbing context than females.