Hypoxia and the antipredator behaviours of fishes

Hypoxia is a phenomenon occurring in marine coastal areas with increasing frequency. While hypoxia has been documented to affect fish activity and metabolism, recent evidence shows that hypoxia can also have a detrimental effect on various antipredator behaviours. Here, we review such evidence with a focus on the effect of hypoxia on fish escape responses, its modulation by aquatic surface respiration (ASR) and schooling behaviour. The main effect of hypoxia on escape behaviour was found in responsiveness and directionality. Locomotor performance in escapes was expected to be relatively independent of hypoxia, since escape responses are fuelled anaerobically. However, hypoxia decreased locomotor performance in some species (Mugilidae) although only in the absence of ASR in severe hypoxia. ASR allows fish to show higher escape performance than fish staying in the water column where hypoxia occurs. This situation provides a trade-off whereby fish may perform ASR in order to avoid the detrimental effects of hypoxia, although they would be subjected to higher exposure to aerial predation. As a result of this trade-off, fishes appear to minimize surfacing behaviour in the presence of aerial predators and to surface near shelters, where possible. For many fish species, schooling can be an effective antipredator behaviour. Severe hypoxia may lead to the disruption of the school unit. At moderate levels, hypoxia can increase school volume and can change the shuffling behaviour of individuals. By altering school structure and dynamics, hypoxia may affect the well functioning of schooling in terms of synchronization and execution of antipredator manoeuvres. School structure and volume appear to be the results of numerous trade-offs, where school shape may be dictated by the presence of predators, the need for energy saving via hydrodynamic advantages and oxygen level. The effects of hypoxia on aquatic organisms can be taxon specific. While hypoxia may not necessarily increase the vulnerability of fish subject to predation by other fish (since feeding in fish also decreases in hypoxia), predators from other taxa such as birds, jellyfish or aquatic mammals may take advantage of the detrimental effects of hypoxia on fish escape ability. Therefore, the effect of hypoxia on fish antipredator behaviours may have major consequences for the composition of aquatic communities.     

Should I stay or should I go? The Ectodysplasin locus is associated with behavioural differences in threespine stickleback

Adaptive divergence may be facilitated if morphological and behavioural traits associated with local adaptation share the same genetic basis. It is therefore important to determine whether genes underlying adaptive morphological traits are associated with variation in behaviour in natural populations. Positive selection on low-armour alleles at the Ectodysplasin (Eda) locus in threespine stickleback has led to the repeated evolution of reduced armour, following freshwater colonization by fully armoured marine sticklebacks. This adaptive divergence in armour between marine and freshwater populations would be facilitated if the low allele conferred a behavioural preference for freshwater environments. We experimentally tested whether the low allele is associated with preference for freshwater by measuring the preference of each Eda genotype for freshwater versus saltwater after acclimation to either salinity. We found no association between the Eda low allele and preference for freshwater. Instead, the low allele was significantly associated with a reduced preference for the acclimation environment. This behaviour may facilitate the colonization of freshwater habitats from the sea, but could also hinder local adaptation by promoting migration of low alleles between marine and freshwater environments.     

Invertebrate predation selects for the loss of a morphological antipredator trait

Antagonistic selection by different predators has been suggested to underlie variation in morphological antipredator traits among and within species. Direct empirical proof is equivocal, however, given the potential interrelationships of morphological and behavioral traits. Here, we tested whether spines in larvae of the dragonfly Leucorrhinia caudalis, which are selected for by fish predators, are selected against by invertebrate aeshnid predators. Using a manipulative approach by cutting spines instead of making comparisons among species or inducing spines, we were able to decouple the presence of spines from other potentially covarying morphological antipredator traits. Results showed survival selection for the loss of spines imposed by invertebrate predation. Moreover, spined and nonspined larval L. caudalis did not differ in the key antipredator behaviors, activity level, and escape burst swimming speed. The observed higher mortality of spined larvae can therefore be directly linked to selection by aeshnid predation against spines.     

Small scale application and assessment of a Index of Biotic Integrity for a large boreal river

Modifications and use of Karr’s Index of Biotic Integrity (IBI) for assessing the effects of anthropogenic impacts to aquatic ecosystems have typically occurred using data collected at the macro scale. However, some non-point sources of habitat degradation occur at small scales. One possible source of perturbation to fish habitat in boreal rivers is the application of rip rap shoreline armouring in human use areas. In this study we assess the use of IBI in a small scale setting and discuss the potential impact of rip rap shoreline armouring. We captured small and juvenile fishes weekly during 2002–2003 from 12 sample sites within the littoral zone of a human use area using a modified beach seine. Principal component analysis (PCA) was performed on the data to examine the relationship between species composition and IBI scores. We also performed PCA on the IBI metrics to assess our modifications. The IBI method produced higher scores for armoured sites than for unarmoured sites. We found a strong rank order correlation (Spearman’s ρ > 0.93; p < 0.001) between the modified IBI scores and the first principal component, suggesting that Karr’s original empirically-based IBI is strongly linked to species composition. We found a high degree of redundancy between the metrics of the IBI that validate our modifications. These results suggest that IBI can be a suitable method for assessing non-point impacts from within a small study area. Our results also indicate that fish habitat from rip rap armoured sites within the test area had consistently higher IBI scores that unarmoured sites.     

Hissing females of great tits (Parus major) have lower breeding success than non‐hissing individuals

Antipredator strategies vary remarkably between individuals within populations. Parents tend to take greater risks when brood value is increased. Moreover, individuals consistently differ in a whole suite of correlated behaviours that may cause distinctive responses to predators. It is likely that individual differences in antipredator behaviour may co‐vary with proxies for fitness such as reproductive success. We used a 4‐year data from wild great tits (Parus major) to test whether passive and active antipredator strategies (females with no response vs. those giving hissing calls towards a nest predator) during the incubation stage can reflect variation in breeding success. Although clutch size did not depend on hissing behaviour, the number of surviving offspring from eggs and neonates to fledglings was higher for non‐hissing than hissing birds. We conclude that females with distinct antipredator strategies can prioritize different fitness components.     

Foraging ecology drives social information reliance in an avian eavesdropping community

Vertebrates obtain social information about predation risk by eavesdropping on the alarm calls of sympatric species. In the Holarctic, birds in the family Paridae function as sentinel species; however, factors shaping eavesdroppers' reliance on their alarm calls are unknown. We compared three hypothesized drivers of eavesdropper reliance: (a) foraging ecology, (b) degree of sociality, and (c) call relevance (caller‐to‐eavesdropper body‐size difference). In a rigorous causal‐comparative design, we presented Tufted Titmouse (Baeolophus bicolor) alarm calls to 242 individuals of 31 ecologically diverse bird species in Florida forests and recorded presence/absence and type (diving for cover or freezing in place) of response. Playback response was near universal, as individuals responded to 87% of presentations (N = 211). As an exception to this trend, the sit‐and‐wait flycatcher Eastern Phoebe (Sayornis phoebe) represented 48% of the nonresponses. We tested 12 predictor variables representing measures relevant to the three hypothesized drivers, distance to playback speaker, and vulnerability at time of playback (eavesdropper's microhabitat when alarm call is detected). Using model‐averaged generalized linear models, we determined that foraging ecology best predicted playback response, with aerial foragers responding less often. Foraging ecology (distance from trunk) and microhabitat occupied during playback (distance to escape cover) best predicted escape behavior type. We encountered a sparsity of sit‐and‐wait flycatchers (3 spp.), yet their contrasting responses relative to other foraging behaviors clearly identified foraging ecology as a driver of species‐specific antipredator escape behavior. Our findings align well with known links between the exceptional visual acuity and other phenotypic traits of flycatchers that allow them to rely more heavily on personal rather than social information while foraging. Our results suggest that foraging ecology drives species‐specific antipredator behavior based on the availability and type of escape cover.     

Predator–prey interactions,flight initiation distance and brain size

Prey avoid being eaten by assessing the risk posed by approaching predators and responding accordingly. Such an assessment may result in prey–predator communication and signalling, which entail further monitoring of the predator by prey. An early antipredator response may provide potential prey with a selective advantage, although this benefit comes at the cost of disturbance in terms of lost foraging opportunities and increased energy expenditure. Therefore, it may pay prey to assess approaching predators and determine the likelihood of attack before fleeing. Given that many approaching potential predators are detected visually, we hypothesized that species with relatively large eyes would be able to detect an approaching predator from afar. Furthermore, we hypothesized that monitoring of predators by potential prey relies on evaluation through information processing by the brain. Therefore, species with relatively larger brains for their body size should be better able to monitor the intentions of a predator, delay flight for longer and hence have shorter flight initiation distances than species with smaller brains. Indeed, flight initiation distances increased with relative eye size and decreased with relative brain size in a comparative study of 107 species of birds. In addition, flight initiation distance increased independently with size of the cerebellum, which plays a key role in motor control. These results are consistent with cognitive monitoring as an antipredator behaviour that does not result in the fastest possible, but rather the least expensive escape flights. Therefore, antipredator behaviour may have coevolved with the size of sense organs, brains and compartments of the brain involved in responses to risk of predation.     

Trait-dependency of trophic interactions in zooplankton food webs

Anthropogenic change in the abundance or identity of dominant top predators may induce reorganizations in whole food webs. Predicting these reorganizations requires identifying the biological rules that govern trophic niches. However, we still lack a detailed understanding of the respective contributions of body size, behaviour (e.g. match between predator hunting mode and prey antipredator strategy), phylogeny and/or ontogeny in determining both the presence and strength of trophic interactions. Here, we address this question by measuring zooplankton numerical response to fish predators in lake enclosures. We compared the fit to zooplankton count data of models grouping zooplankters based either on 1) body sizes, 2) antipredator behaviour, 3) body size combined with antipredator behaviour or on 4) phylogeny combined with ontogeny (i.e. different life stages of copepods). Body size was a better predictor of zooplankton numerical response to fish than antipredator behaviour, but combining body size and behaviour provided even better predictions. Models based on phylogeny combined with ontogeny clearly outperformed those based on other zooplankton grouping rules, except when phylogeny was poorly resolved. Removing ontogenetic information plagued the predictive power of the highly-resolved (genus-level) phylogenetic grouping but not of medium-resolved or poorly-resolved phylogenetic grouping. Our results support the recent use of phylogeny as a superior surrogate for traits controlling trophic niches, and further highlight the added value of combining phylogeny with ontogenetic traits. Further improvements in our mechanistic understanding of how trophic networks are shaped are bound to uncovering the trophic traits captured by phylogeny and ontogeny, but that currently remain hidden to us.     

Relative Cost/Benefit Trade‐Off Between Cover‐Seeking and Escape Behaviour in an Ancestral Fish: The Importance of Structural Habitat Heterogeneity

Fleeing from predators and moving into protective habitats are two common antipredator behaviours in the animal kingdom. Surprisingly, the relative cost/benefit trade‐off of each behavioural option has rarely been examined empirically. Here, we investigate the interplay between decisions surrounding escape behaviour and rocky microhabitat occupancy in lake sturgeon, Acipenser fulvescens. In high‐risk clear‐water environments, sturgeon responded to danger by evoking an escape response and by seeking cover in rocky microhabitats. However, in low‐risk turbid environments, we found that sturgeon responded to danger by seeking cover in rocky microhabitats, but not fleeing to a significant degree. Cover‐seeking behaviour may therefore be a relatively low‐cost/high‐benefit antipredator strategy. These findings highlight the importance of structural habitat heterogeneity for prey animals in predator‐dominated landscapes.     

Contagious fear: Escape behavior increases with flock size in European gregarious birds

Flight initiation distance (FID), the distance at which individuals take flight when approached by a potential (human) predator, is a tool for understanding predator–prey interactions. Among the factors affecting FID, tests of effects of group size (i.e., number of potential prey) on FID have yielded contrasting results. Group size or flock size could either affect FID negatively (i.e., the dilution effect caused by the presence of many individuals) or positively (i.e., increased vigilance due to more eyes scanning for predators). These effects may be associated with gregarious species, because such species should be better adapted to exploiting information from other individuals in the group than nongregarious species. Sociality may explain why earlier findings on group size versus FID have yielded different conclusions. Here, we analyzed how flock size affected bird FID in eight European countries. A phylogenetic generalized least square regression model was used to investigate changes in escape behavior of bird species in relation to number of individuals in the flock, starting distance, diet, latitude, and type of habitat. Flock size of different bird species influenced how species responded to perceived threats. We found that gregarious birds reacted to a potential predator earlier (longer FID) when aggregated in large flocks. These results support a higher vigilance arising from many eyes scanning in birds, suggesting that sociality may be a key factor in the evolution of antipredator behavior both in urban and rural areas. Finally, future studies comparing FID must pay explicit attention to the number of individuals in flocks of gregarious species.     

Proximate causes of variation in dermal armour: insights from armadillo lizards

Although it is widely assumed that body armour in animals evolved to thwart predator attacks, assessing the role that predators may play in shaping defensive morphologies has proven to be difficult. Recent studies suggest that body armour might be influenced by additional factors besides predation, and/or even by sexual selection. We investigated variation in dermal armour in 13 populations of armadillo lizards Ouroborus cataphractus, spanning the entire distribution range of the species. We obtained thickness measurements of osteoderms – bony plates embedded in dermal layer of the skin – using micro‐ and nano‐computed tomography. Using these data, we examined the effects of predation pressure/risk and climatic variables on dermal armour variation and addressed sexual and ontogenetic influence. Our results show that climate is the only factor affecting variation in dermal armour. Populations inhabiting more arid environments, characterized by low summer precipitation and mild winter temperatures, are relatively more armoured than those present in less arid environments. In contrast to our expectations, predation pressure or perceived predation risk was not associated with osteoderm thickness. The results of our study support the idea that the evolution of defensive traits might not be driven exclusively by predator–prey interactions, but could be moulded by environmental factors. In particular, we highlight the role of dermal armour as a potentially important mechanism to reduce evaporative water loss in arid environments.     

Ancient DNA from the extinct South American giant glyptodont Doedicurus sp. (Xenarthra: Glyptodontidae) reveals that glyptodonts evolved from Eocene armadillos

Glyptodonts were giant (some of them up to ~2400 kg), heavily armoured relatives of living armadillos, which became extinct during the Late Pleistocene/early Holocene alongside much of the South American megafauna. Although glyptodonts were an important component of Cenozoic South American faunas, their early evolution and phylogenetic affinities within the order Cingulata (armoured New World placental mammals) remain controversial. In this study, we used hybridization enrichment and high‐throughput sequencing to obtain a partial mitochondrial genome from Doedicurus sp., the largest (1.5 m tall, and 4 m long) and one of the last surviving glyptodonts. Our molecular phylogenetic analyses revealed that glyptodonts fall within the diversity of living armadillos. Reanalysis of morphological data using a molecular ‘backbone constraint’ revealed several morphological characters that supported a close relationship between glyptodonts and the tiny extant fairy armadillos (Chlamyphorinae). This is surprising as these taxa are among the most derived cingulates: glyptodonts were generally large‐bodied and heavily armoured, while the fairy armadillos are tiny (~9–17 cm) and adapted for burrowing. Calibration of our phylogeny with the first appearance of glyptodonts in the Eocene resulted in a more precise timeline for xenarthran evolution. The osteological novelties of glyptodonts and their specialization for grazing appear to have evolved rapidly during the Late Eocene to Early Miocene, coincident with global temperature decreases and a shift from wet closed forest towards drier open woodland and grassland across much of South America. This environmental change may have driven the evolution of glyptodonts, culminating in the bizarre giant forms of the Pleistocene.     

Escape from predators and genetic variance in birds

Predation is a common cause of death in numerous organisms, and a host of antipredator defences have evolved. Such defences often have a genetic background as shown by significant heritability and microevolutionary responses towards weaker defences in the absence of predators. Flight initiation distance (FID) is the distance at which an individual animal takes flight when approached by a human, and hence, it reflects the life‐history compromise between risk of predation and the benefits of foraging. Here, we analysed FID in 128 species of birds in relation to three measures of genetic variation, band sharing coefficient for minisatellites, observed heterozygosity and inbreeding coefficient for microsatellites in order to test whether FID was positively correlated with genetic variation. We found consistently shorter FID for a given body size in the presence of high band sharing coefficients, low heterozygosity and high inbreeding coefficients in phylogenetic analyses after controlling statistically for potentially confounding variables. These findings imply that antipredator behaviour is related to genetic variance. We predict that many threatened species with low genetic variability will show reduced antipredator behaviour and that subsequent predator‐induced reductions in abundance may contribute to unfavourable population trends for such species.     

Does Locomotor Ability Influence Flight Initiation Distance in Yellow‐Bellied Marmots?

Flight initiation distance (FID) is the distance between a potential threat and the point at which a potential prey flees. Animals may modify their FID to compensate for increased risk generated by external/extrinsic factors such as habitat type, visibility, group size, time of year, predator‐approach velocity, and distance to burrow, as well as internal/intrinsic factors such as physical condition, body temperature, crypsis, and morphological antipredator defenses. The intrinsic speed at which an animal can escape a predator is a factor that should influence FID. We studied the relationship between an individual's intrinsic escape speed and FID in yellow‐bellied marmots (Marmota flaviventris) to determine whether marmots compensated for slower escape speeds by fleeing at greater distances. We found no evidence of risk compensation. Rather, we found that slower marmots tolerated closer approaches. This behavioral syndrome may be explained by a coevolution of FID and escape speed in determining an individual's antipredator behavior, an idea upon which we expand.     

Fight or flight: antipredator strategies of baleen whales

• 1 The significance of killer whale Orcinus orca predation on baleen whales (Mysticeti) has been a topic of considerable discussion and debate in recent years. Discourse has been constrained by poor understanding of predator‐prey dynamics, including the relative vulnerability of different mysticete species and age classes to killer whales and how these prey animals avoid predation. Here we provide an overview and analysis of predatory interactions between killer whales and mysticetes, with an emphasis on patterns of antipredator responses.
• 2 Responses of baleen whales to predatory advances and attacks by killer whales appear to fall into two distinct categories, which we term the fight and flight strategies. The fight strategy consists of active physical defence, including self‐defence by single individuals, defence of calves by their mothers and coordinated defence by groups of whales. It is documented for five mysticetes: southern right whale Eubalaena australis, North Atlantic right whale Eubalaena glacialis, bowhead whale Balaena mysticetus, humpback whale Megaptera novaeangliae and grey whale Eschrichtius robustus. The flight strategy consists of rapid (20–40 km/h) directional swimming away from killer whales and, if overtaken and attacked, individuals do little to defend themselves. This strategy is documented for six species in the genus Balaenoptera.
• 3 Many aspects of the life history, behaviour and morphology of mysticetes are consistent with their antipredator strategy, and we propose that evolution of these traits has been shaped by selection for reduced predation. Fight species tend to have robust body shapes and are slow but relatively manoeuvrable swimmers. They often calve or migrate in coastal areas where proximity to shallow water provides refuge and an advantage in defence. Most fight species have either callosities (rough and hardened patches of skin) or encrustations of barnacles on their bodies, which may serve (either primarily or secondarily) as weapons or armour for defence. Flight species have streamlined body shapes for high‐speed swimming and they can sustain speeds necessary to outrun pursuing killer whales (>15–20 km/h). These species tend to favour pelagic habitats and calving grounds where prolonged escape sprints from killer whales are possible.
• 4 The rarity of observed successful attacks by killer whales on baleen whales, especially adults, may be an indication of the effectiveness of these antipredator strategies. Baleen whales likely offer low profitability to killer whales, relative to some other marine mammal prey. High‐speed pursuit of flight species has a high energetic cost and a low probability of success while attacks on fight species can involve prolonged handling times and a risk of serious injury.

     

Temporal learning of predation risk by embryonic amphibians

For prey species that rely on learning to recognize their predators, natural selection should favour individuals able to learn as early as possible. The earliest point at which individuals can gather information about the identity of their potential predators is during the embryonic stage. Indeed, recent experiments have demonstrated that amphibians can learn to recognize predators prior to hatching. Here, we conditioned woodfrog embryos to recognize predatory salamander cues either in the morning or in the evening, and subsequently exposed the two-week-old tadpoles to salamander cues either in the morning or in the evening, and recorded the intensity of their antipredator behaviour. The data indicate that amphibians learn to recognize potential predators while still in the egg, and also learn the temporal component of this information, which they use later in life, to adjust the intensity of their antipredator responses throughout the day.     

Bold coloration and the evolution of aposematism in terrestrial carnivores

Several species of terrestrial carnivores (Mammalia: Carnivora) have bold contrasting color patterns that, in some species, apparently signal possession of noxious anal gland secretions, or even physical strength and great ferocity; yet the evolutionary drivers of both placement and patterning of these contrasting pelage colors on the body, and the ecological selection pressures underlying them, have yet to be systematically examined. Here we explore these issues and find not only that both boldly colored and dichromatic species do indeed often use anal gland secretions for defense, but also that such species are stockier, and live in more exposed habitats where other forms of antipredator defense are limited. We also show that white dorsa are found in sprayers that are primarily nocturnal; that horizontal stripes are found in species that have an ability to spray anal secretions accurately; and that facial stripes are found in burrowing species that typically leave only their heads exposed to attack. Our phylogenetic reconstructions suggest that aposematic coloration has evolved more than once in terrestrial carnivores. We finish by outlining five evolutionary routes for patterns of pelage coloration in this taxon.     

Antipredator behaviour of invasive geckos in response to chemical cues from snakes

Antipredator behaviours and the ability to appropriately assess predation risk contribute to increased fitness. Predator avoidance can be costly; however, so we expect prey to most strongly avoid predators that pose the greatest risk (i.e., prey should show threat sensitivity). For invasive species, effectively assessing the relative risk posed by predators in the new environment may help them establish in new environments. We examined the antipredator behaviour of introduced Asian house geckos, Hemidactylus frenatus (Schlegel), by determining if they avoided shelters scented with the chemical cues of native predatory snakes (spotted pythons, Antaresia maculosa [Peters]; brown tree snakes, Boiga irregularis [Merrem]; common tree snakes, Dendrelaphis punctulata [Grey]; and carpet pythons, Morelia spilota [Lacépède]). We also tested if Asian house geckos collected from vegetation vs. anthropogenic substrates (buildings) responded differently to the chemical cues of predatory snakes. Asian house geckos did not show a generalised antipredator response, that is, they did not respond to the chemical cues of all snakes in the same way. Asian house geckos avoided the chemical cues of carpet pythons more strongly than those of other snake species, providing some support for the threat‐sensitivity hypothesis. There was no difference in the antipredator behaviour of Asian house geckos collected from buildings vs. natural vegetation, suggesting that individuals that have invaded natural habitats have not changed their antipredator behaviour compared to urban individuals. Overall, we found some evidence indicating Asian house geckos are threat‐sensitive to some Australian predacious snakes.     

Predator-induced respiratory responses in juveniles of vendace Coregonus albula, whitefish C. lavaretus, perch Perca fluviatilis and roach Rutilus rutilus

Predator-induced respiratory responses of juvenile vendace, whitefish, perch and roach were studied in an intermittent-flow respirometer by creating visual contact between test fishes and predators (juvenile northern pike). Vendace and whitefish always responded to the presence of pike with increased oxygen consumption. The response of perch was the opposite: oxygen consumption decreased to near the standard respiratory level. Roach responded more variably: some individuals increased their oxygen uptake while others decreased it. Changes in the rate of respiration during exposure to predation are supposed to be caused by the differences in locomotory activity due to induced antipredator behaviour. According to their responses, these species could be grouped into escapers (coregonids), hiders (perch) or indeterminates (roach). The species-specific differences in the antipredator behaviour originate in morphological and physiological characteristics which together determine the effectiveness of a particular antipredator style (i.e. either hiding or escaping).     

Adaptive significance of antipredator behaviour in artiodactyls

We used comparative data to test functional hypotheses for 17 antipredator behaviour patterns in artiodactyls. We examined the literature for hypotheses about auditory and visual signals, defensive behaviour and group-related antipredator behaviour in this taxon and derived a series of predictions for each hypothesis. Next, we documented occurrences of these behaviour patterns and morphological, ecological and behavioural variables for 200 species and coded them in binary format. We then pitted presence of an antipredator behaviour against presence of an independent variable for cervids, bovids and all artiodactyls together using nonparametric tests. Finally, we reanalysed the data using Maddison's (1990, Evolution, 44, 539-557) concentrated-changes tests and a consensus molecular and taxonomic phylogeny. We found evidence that snorting is both a warning signal to conspecifics and a pursuit-deterrent signal, lack of evidence that whistling alerts conspecifics and indications that foot stamping is a visual signal to warn group members. Evidence suggested that tail flagging was a signal to both conspecifics and predators, that bounding, leaping and stotting were used both as a signal and to clear obstacles and that prancing functioned similarly to foot stamping. Analyses of tail flicking, zigzagging and tacking were equivocal. We confirmed that inspection occurs in large groups, freezing enhances crypticity, and species seeking refuge in cliffs tend to be small. Entering water and attacks on predators had few correlates. Finally, group living, a putative antipredator adaptation, was associated with large body size and species living in open habitats, confirming Jarman's (1974, Behaviour, 48, 215-267) classic hypothesis. Bunching and group attack apparently deter predators. Despite limitations, comparative and systematic analyses can bolster adaptive hypotheses and raise new functional explanations for antipredator behaviour patterns in general.