Age and sex influence marmot antipredator behavior during periods of heightened risk

Behavioural changes in aposematic Heliconius melpomene butterflies in response to their predatory bird calls

Prey-predator interactions have resulted in the evolution of many anti-predatory traits. One of them is the ability for prey to listen to predators and avoid them. Although prey anti-predatory behavioural responses to predator auditory cues are well described in a wide range of taxa, studies on whether butterflies change their behaviours in response to their predatory calls are lacking. Heliconius butterflies are unpalatable and form Müllerian mimicry rings as morphological defence strategies against their avian predators. Like many other butterflies in the Nymphalidae family, some Heliconius butterflies possess auditory organs, which are hypothesized to assist with predator detection. Here we test whether Heliconius melpomene change their behaviour in response to their predatory bird calls by observing the behaviour of male and female H. m. plessini exposed to calls of Heliconius avian predators: rufous-tailed jacamar, migratory Eastern kingbird, and resident tropical kingbird. We also exposed them to the calls of the toco toucan, a frugivorous bird as a control bird call, and an amplified greenhouse background noise as a noise control. We found that individuals changed their behaviour in response to jacamar calls only. Males increased their walking and fluttering behaviour, while females did not change their behaviour during the playback of the jacamar call. Intersexual behaviours like courtship, copulation, and abdomen lifting did not change in response to bird calls. Our findings suggest that despite having primary predatory defences like toxicity and being in a mimicry ring, H. m. plessini butterflies changed their behaviour in response to predator calls. Furthermore, this response was predator specific, as H. m. plesseni did not respond to either the Eastern kingbird or the tropical kingbird calls. This suggests that Heliconius butterflies may be able to differentiate predatory calls, and potentially the birds associated with those calls.

Watch out! High vigilance at small waterholes when alone in open trees

An animal's environment contains many risks causing animals to scan their environment for potential predators and threats from conspecifics. How much time they invest in such vigilance depends on environmental and social factors. Most vigilance studies have been conducted in a foraging context with little known about vigilance in other contexts. Here we investigated vigilance of Gouldian finches at waterholes considering environmental and social factors. Gouldian finches are colour polymorphic with two main head colours in both sexes co-occurring in the same population, black-headed and red-headed. Data collection was done on birds sitting in trees surrounding waterholes by measuring the frequency of head movements, which reflects how frequently they change their field of view, i.e., scan different areas in their environment. A higher frequency generally reflects higher vigilance. Gouldian finches had a higher frequency of head movements when at small waterholes and when sitting in open, leafless trees. Moreover, head movements were higher when birds were alone in the tree as compared to groups of birds. Finally, birds in same head colour morph groups had a higher frequency of head movements than birds in mixed head colour groups. Results indicate heightened vigilance with increased perception of predation risk (small waterholes, open exposed perch, when alone) but that social vigilance also played a role (group composition) with particularly the aggressive red-headed birds being more vigilant when together with other red-headed birds. Future research should investigate the effect of smaller waterholes as global warming will cause smaller waterholes to become more common for longer periods of time, which can increase stress in the birds.

Animal-friendly behavioral testing in field studies: examples from ground squirrels

Field studies of behavior provide insight into the expression of behavior in its natural ecological context and can serve as an important complement to behavioral studies conducted in the lab under controlled conditions. In addition to naturalistic observations, behavioral testing can be an important component of field studies of behavior. This mini review evaluates a sample of behavioral testing methods in field studies to identify ways in which behavioral testing can be animal-friendly and generate ethologically relevant data. Specific examples, primarily from studies of ground squirrels, are presented to illustrate ways in which principles of animal-friendly behavioral testing can be applied to and guide testing methods. Tests conducted with animals in their natural habitat and that elicit naturally occurring behavioral responses can minimize stress and disturbance for animals, as well as disruption of the larger ecosystem, and can have high ethological validity. When animals are trapped or handled as part of a study, behavioral testing can be incorporated into handling procedures to reduce overall disturbance. When behavior is evaluated in a testing arena, the arena can be designed to resemble natural conditions to increase the ethological relevance of the test. Efforts to minimize time spent in testing arenas can also reduce disturbance to animals. Adapting a behavioral test to a species or habitat conditions can facilitate reduced disruption to subjects and increased ethological relevance of the test.

When to Return to Normal? Temporal Dynamics of Vigilance in Four Situations

Vigilance is an important behaviour to monitor the environment from detecting predators to tracking conspecifics. However, little is known about how vigilance changes over time either without disturbance (vigilance decrement) or after a change occurred. The time course of vigilance can indicate how animals perceive a situation and the potential mechanism used to deal with it. I investigated the time course of vigilance in Gouldian Finches in four situations (familiar environment, two changed environments–novel object at a neutral location (exploration trial) or above the feeder (neophobia trial), novel environment). The frequency of head movements was assessed in four consecutive 15-min blocks in same sex pairs with a high frequency generally seen as indicative of high vigilance. Vigilance decreased over time in the familiar situation indicating vigilance decrement with a similar time course in the exploration trial. Vigilance was consistently high in the neophobia trial and only returned to normal in the last block. Finally, vigilance plummeted in the novel environment and did not return to normal within an hour. Results suggest that perceived threats affected vigilance and that information gathering reduced uncertainty allowing vigilance to return to normal levels but with different time courses depending on the situation.

Intersexual differences in the number of genes differentially expressed in wild mammals in response to predation risk

Predation is a psychological stressor in prey animals. Besides direct killing and consumption by predators, the perception of predation risk indirectly influence prey population behavior, dynamics and physiology. Few studies identified the transcriptomic response associated with predator presence/abundance in natural populations and uncontrolled settings. However, to our knowledge, intersexual differences in the number of genes whose expression change in response to high predation risk have not been previously reported in wild mammals. Here, by using publicly available gene expression data in wild yellow-bellied marmots (Marmota flaviventer), we found that the number of differentially expressed genes in response to predator stress is higher in female marmots (n = 516) than males (n = 387). Only a small percentage of these differentially expressed genes (n = 36) are shared between the sexes, and that the most of the differentially expressed genes are expressed in a sex-specific manner in response to predation stress. Overall, our results provide new insight into sex-specific variation in gene expression changes in wild mammals under high predation risk.

Morph Composition Matters in the Gouldian Finch (Chloebia gouldiae): Involvement of Red-Headed Birds Increases Vigilance

Animals invest in costly vigilance to detect threats. Joining groups reduces these costs, which can be further reduced in mixed-species assemblages. In colour-polymorphic species, morphs often experience different predation pressure and vary in a variety of traits. However, little is known about differences in vigilance or how group composition affects vigilance. The aim was to investigate whether higher conspicuousness increased vigilance and whether vigilance was reduced in mixed-morph groups like in mixed-species assemblages. I tested vigilance in the colour-polymorphic Gouldian Finch (Chloebia gouldiae). Same sex pairs of different age and of either pure (red-red or black-black) or mixed head colour were exposed to three contexts (familiar, changed and novel environment) and head movements were recorded. All birds reduced the frequency of head movements with increasing novelty, indicating different vigilance strategies (switching from a searching to a tracking strategy) depending on the situation. While vigilance did not differ between morphs, morph composition mattered. Black-headed pairs made fewer head movements than mixed-head colour pairs. Results indicated that conspicuousness did not affect vigilance, possibly due to existing adaptations to reduce predation risk. However, whenever red-headed birds were involved, vigilance increased either because of higher group conspicuousness or prevalence of aggression.

Intrapopulation variation in the behavioral responses of dwarf mongooses to anthropogenic noise

Anthropogenic noise is an increasingly widespread pollutant, with a rapidly burgeoning literature demonstrating impacts on humans and other animals. However, most studies have simply considered if there is an effect of noise, examining the overall cohort response. Although substantial evidence exists for intraspecific variation in responses to other anthropogenic disturbances, this possibility has received relatively little experimental attention with respect to noise. Here, we used field-based playbacks with dwarf mongooses (Helogale parvula) to test how traffic noise affects vigilance behavior and to examine potential variation between individuals of different age class, sex, and dominance status. Foragers exhibited a stronger immediate reaction and increased their subsequent vigilance (both that on the ground and as a sentinel) in response to traffic-noise playback compared with ambient-sound playback. Traffic-noise playback also resulted in sentinels conducting longer bouts and being more likely to change post height or location than in ambient-sound playback. Moreover, there was evidence of variation in noise responses with respect to age class and dominance status but not sex. In traffic noise, foraging pups were more likely to flee and were slower to resume foraging than adults; they also tended to increase their vigilance more than adults. Dominants were more likely than subordinates to move post during sentinel bouts conducted in traffic-noise trials. Our findings suggest that the vigilance–foraging trade-off is affected by traffic noise but that individuals differ in how they respond. Future work should, therefore, consider intrapopulation response variation to understand fully the population-wide effects of this global pollutant.

The effect of age on vigilance: a longitudinal study with a precocial species

Vigilance allows prey species to detect predators before it is too late to escape. While the adaptive value of vigilance has become clearer over the years, developmental questions have attracted little attention. I explored the effect of age and group size on vigilance in a precocial species, the domestic fowl (Gallus gallus domesticus). I recorded vigilance in groups of various sizes in juveniles and one year later in adults. Vigilance decreased with group size in juveniles and to a lesser extent in adults. Juveniles tested alone showed longer feeding and vigilance bouts than adults reflecting their inexperience with predation threats and more rapid satiation, respectively. Adults in larger groups were more vigilant reflecting the need to monitor aggressive conspecifics in addition to predators. Gradual acquisition of information about risk posed by predators and conspecifics and feeding constraints influenced the expression of vigilance as a function of age in this species.

Changes in physiological stress and behaviour in semi-free-ranging red-capped mangabeys (Cercocebus torquatus) following antiparasitic treatment

Parasites are ubiquitous in wildlife populations, but physiological and behavioural responses of hosts to infection are difficult to measure. We experimentally treated semi-free-ranging red-capped mangabeys (Cercocebus torquatus) in Nigeria with antiparasitic drugs and examined subsequent changes in glucocorticoid production and individual behaviour. Because both parasites and stress impact energy balance and health, we measured (i) behavioural time re-allocation via activity budgets, (ii) social relationships (e.g. social connectivity and dominance hierarchy stability) and (iii) body condition. We collected triplicate faecal samples (n = 441) from 49 individuals prior to and following treatment. Cortisol levels fluctuated in parallel with parasite abundance. Elevations in cortisol, but not parasitism, were related to reduced body condition. Behaviour also shifted according to infection status, with uninfected individuals spending more time foraging and less time resting and vigilant compared with when they were infected. Time spent feeding, travelling or socializing did not differ between pre- and post-treatment time periods. Group cohesion, but not dominance stability, changed following treatment, suggesting parasite-induced social avoidance. Together, these findings show a coordinated response to infection that promotes host tolerance through stress and energy conservation, reduces transmission risk and increases protection when infected hosts are vulnerable.

Anti-predator behaviour of kudu and impala in response to mimicked African wild dog presence: do age and sex matter?

Predators not only prey upon certain prey species, but also on certain age–sex classes within species. Predation risk and an individual’s response to this risk might therefore vary with an individual’s characteristics. We examined the proportion of time different age–sex classes of kudu (Tragelaphus strepsiceros) and impala (Aepyceros melampus) spent high quality vigilant (costly vigilance that detracts from all other activities) in response to mimicked predation risk by African wild dogs (Lycaon pictus). For both species predation risk was the main factor determining the investment in high quality vigilance behaviour. Age–sex class-specific responses were not related to age–sex class specific lethality risk presented by African wild dogs. For impala, regardless of predation risk, age seemed to have some effect on the investment in high quality vigilance with sub-adult impala spending more time high quality vigilant than adult impala, which is possibly why African wild dogs predominantly preyed upon adult impala.

Hunger-dependent and Sex-specific Antipredator Behaviour of Larvae of a Size-dimorphic Mosquito

1. Modification of behaviors in the presence of predators or predation cues is widespread among animals. Costs of a behavioral change in the presence of predators or predation cues depend on fitness effects of lost feeding opportunities and, especially when organisms are sexually dimorphic in size or timing of maturation, these costs are expected to differ between the sexes. 2. Larval Aedes triseriatus (Say) (Diptera: Culicidae) were used to test the hypothesis that behavioral responses of the sexes to predation cues have been selected differently due to different energy demands. 3. Even in the absence of water-borne predation cues, hungry females (the larger sex) spent more time browsing than did males, indicating a difference in energy needs. 4. In the presence of predation cues, well-fed larvae of both sexes reduced their activity more than did hungry larvae, and males shifted away from high-risk behaviors to a greater degree than did females, providing the first evidence of sex-specific antipredator behavior in foraging mosquito larvae. 5. Because sexual size dimorphism is common across taxa, and energetic demands are likely correlated with size dimorphism, this research demonstrates the importance of investigating sex specific behavior and behavioral responses to enemies and cautions against generalizing results between sexes.

Individual traits influence vigilance in wild female eastern grey kangaroos

Vigilance is an essential component of antipredator behaviour and is also used to monitor conspecifics, but is traded off against feeding in herbivores. This trade-off can be influenced by variation in many environmental, social and individual traits. Our aim was to test the relationship between individual-level traits, including boldness, body condition and reproductive state, and vigilance, while controlling for environmental and social variables. Using multiple 5-min video samples of 30 foraging, individually recognisable, female eastern grey kangaroos (Macropus giganteus) at Sundown National Park in Queensland, we investigated individual-level variation in the duration, intensity and target of vigilance behaviour during foraging. On separate occasions, we used flight-initiation distance tests to measure boldness in our kangaroos. Females with longer flight-initiation distances (shyer females) spent more time vigilant, providing preliminary support for studies of animal personality that have suggested that boldness may covary with vigilance. Body condition did not affect the total time spent vigilant, but females in poorer body condition spent more of their vigilance time in low-intensity vigilance. Vigilance patterns were not related to reproductive state, but varied among months and differed between mornings and afternoons, and females spent more time in high-intensity vigilance when further from cover. Even after accounting for all our variables we found that 7% of the variation in total time vigilant and 14% of the variation in vigilance intensity was explained by individual identity. This highlights the importance of individual-level variation in vigilance behaviour.