Optimal escape theory predicts escape behaviors beyond flight initiation distance:risk assessment and escape by striped plateau lizards Sceloporus virgatus

Escape theory predicts that flight initiation distance （FID = distance between predator and prey when escape begins） is longer when risk is greater and shorter when escape is more costly. A few tests suggest that escape theory applies to distance fled. Escape models have not addressed stochastic variables, such as probability of fleeing and of entering refuge, but their economic logic might be applicable. Experiments on several risk factors in the lizard Sceloporus virgatus confirmed all predictions for the above escape variables. FID was greater when approach was faster and more direct, for lizards on ground than on trees, for lizards rarely exposed to humans, for the second of two approaches, and when the predator turned toward lizards rather than away. Lizards fled further during rapid and second consecutive approaches. They were more likely to flee when approached directly, when a predator turned toward them, and during second approaches. They were more likely to enter refuge when approached rapidly. A novel finding is that perch height in trees was unrelated to FID because lizards escaped by moving out of sight, then moving up or down unpredictably. These findings add to a growing body of evidence supporting predictions of escape theory for FID and distance fled. They show that two probabilistic aspects of escape are predictable based on relative predation risk levels. Because individuals differ in boldness, the assessed optimal FID and threshold risks for fleeing and entering refuge are exceeded for an increasing proportion of individuals as risk increases

Generalization of predator recognition:Velvet geckos display anti-predator behaviours in response to chemicals from non-dangerous elapid snakes

Many prey species detect chemical cues from predators and modify their behaviours in ways that reduce their risk ofpredation. Theory predicts that prey should modify their anti-predator responses according to the degree of threat posed by thepredator. That is, prey should show the strongest responses to chemicals of highly dangerous prey, but should ignore or respondweakly to chemicals from non-dangerous predators. However, if anti-predator behaviours are not costly, and predators are rarelyencountered, prey may exhibit generalised antipredator behaviours to dangerous and non-dangerous predators. In Australia, mostelapid snakes eat lizards, and are therefore potentially dangerous to lizard prey. Recently, we found that the nocturnal velvetgecko Oedura lesueurii responds to chemicals from dangerous and non-dangerous elapid snakes, suggesting that it displays generalisedanti-predator behaviours to chemicals from elapid snakes. To explore the generality of this result, we videotaped the behaviourof velvet geckos in the presence of chemical cues from two small elapid snakes that rarely consume geckos: the nocturnalgolden-crowned snake Cacophis squamulosus and the diurnal marsh snake Hemiaspis signata. We also videotaped geckos in trialsinvolving unscented cards (controls) and cologne-scented cards (pungency controls). In trials involving Cacophis and Hemiaspischemicals, 50% and 63% of geckos spent long time periods (> 3 min) freezing whilst pressed flat against the substrate, respectively.Over half the geckos tested exhibited anti-predator behaviours (tail waving, tail vibration, running) in response to Cacophis(67%) or Hemiaspis (63%) chemicals. These behaviours were not observed in control or pungency control trials. Our resultssupport the idea that the velvet gecko displays generalised anti-predator responses to chemical cues from elapid snakes.Generalised responses to predator chemicals may be common in prey species that co-occur with multiple, ecologically similar,dangerous predators [Current Zoology 56 (3): 337-342, 2010].

A highly effective incubation strategy enhanced the urban bird hatch success

Urbanization is currently considered one of the most rapid types of global environmental change.Urban habitats are biotically and abiotically different from their rural areas,i.e.,the ambient temperature,predator,and food availability.These novel challenges create new selection pressures,which allow one to investigate ecoevolutionary responses to contemporary environmental change.A total of 118 breeding nests were monitored for nest predation in both urban and rural areas from 2018 to 2020.We used environmental factors from urban and rural areas and behavioral data from 439 Chinese Blackbird(Turdus mandarinus)valid incubation days to understand the impact of urbanization on the incubation behavior of blackbirds and its adaptation mechanism to the urban environment.Cities have warmer ambient temperatures and lower predation pressures than rural areas.Urban blackbirds chose the incubation strategy with shorter and more bouts,while rural blackbirds selected the incubation strategy with longer and fewer bouts.The plasticity of incubation behavior of urban blackbirds was higher than that of rural areas,and the range of egg temperature was also higher than that of rural areas.In addition,incubation temperature and the number of bouts per day were the key factors affecting the day survival rate of blackbirds,and the hatching rate of urban blackbirds was higher than that of rural blackbirds.Our results provide evidence for behavioral shifts in blackbirds during adaptation to urbanization and support the central role of behavioral adaptation in the successful colonization of new environments by wildlife.These help us understand the behavioral characteristics required for wildlife to live in cities and the urban adaptors faced environmental pressures.

Anthropogenic noise interacts with the predation risk assessment in a free-ranging bird

Anthropogenic noise can affect a number of behavioral,physiological,and ecological aspects of animals from major taxonomic groups,raising serious conservation concerns.For example,noise pollution impacts communicative behavior and perception of signals,movements and distribution,as well as predator–prey interactions,such as hunting success or predator detection and predation risk assessment.We have carried out an experimental playback study,in which we investigated whether exposure to anthropogenic noise(sound of a tractor)distracts free-ranging barn swallows Hirundo rustica from paying attention to an approaching human“predator”(the“cognitive distraction”hypothesis),or whether noise leads to increased responsiveness to this“predator”(the“increased threat”hypothesis).The subjects were male barn swallows attending their breeding territories during the time when the females were incubating.We found that barn swallow males initiated fight at signifcantly greater distances to the approaching human“predator”in the noise treatment than during the quiet control trials.These results suggest that anthropogenic noise causes increased vigilance and reactivity rather than a distraction,enabling birds to avoid the“predator”more quickly.We further discuss the mechanism behind the increased alertness in response to noise and contrast the“increased threat”mechanism,usually tested in previous studies,with an alternative“cognitive sensitization”mechanism.

Scatterhoarding rodents favor higher predation risks for cache sites:The potential for predators to influence the seed dispersal process

Scatterhoarding rodents often place caches in the open where pilferage rates are reduced,suggesting that they tradeoff higher risks of predation for more secure cache sites.We tested this hypothesis in two study systems by measuring predation risks inferred from measures of giving-up densities(GUDs)at known cache sites and other sites for comparison.Rodent GUDs were measured with small trays containing 3 L of fine sand mixed with sunflower seeds.In the first experiment,we relied on a 2-year seed dispersal study in a natural forest to identify caches of eastern gray squirrels(Sciurus carolinensis)and then measured GUDs at:(i)these caches;(ii)comparable points along logs and rocks where rodent activity was assumed highest;and(iii)a set of random points.We found that GUDs and,presumably,predation risks,were higher at both cache and random points than those with cover.At the second site,we measured GUDs of eastern gray squirrels in an open park system and found that GUDs were consistently lowest at the base of the tree compared to more open sites,where previous studies show caching by squirrels to be highest and pilferage rates by naïve competitors to be lowest.These results confirm that predation risks can influence scatterhoarding decisions but that they are also highly context dependent,and that the landscape of fear,now so well documented in the literature,could potentially shape the temporal and spatial patterns of seedling establishment and forest regeneration in systems where scatterhoarding is common.

Effects of Predation by Invasive Western Mosquitofish(Gambusia affinis) on Survival of Eggs,Embryos and Tadpoles of Pelophylax nigromaculatus and Duttaphrynus melanostictus in South China

Alien species are one of the most serious threats to the decline and extinction of native amphibian populations. In this study, we examined the predation of invasive Western Mosquitofish Gambusia affinis on the eggs, embryos, and tadpoles of Duttaphrynus melanostictus and Pelophylax nigromaculatus in south China. Our results suggested that the survival of eggs and embryos remaining in the egg capsules of P. nigromaculatus and D. melanostictus was significantly higher than those removed from the egg capsule at 12-h intervals within 72 h in the presence of G. affinis. The survival of P. nigromaculatus eggs and embryos without egg capsules was significantly lower than those of D. melanostictus without egg capsules. The survival of P. nigromaculatus eggs and embryos with egg capsules was significantly higher than those of D. melanostictus with egg capsules from 24 h to 72 h except for 12 h. The survival of D. melanostictus tadpoles was significantly higher than that of P. nigromaculatus tadpoles in the presence of G. affinis. The survival of Gosner stage 26 tadpoles of P. nigromaculatus was significantly higher than that of Gosner stage 30 tadpoles from 12 h to 60 h, but there were no significant differences at 72 h. In contrast, the survival of Gosner stage 26 tadpoles of D. melanostictus was significantly lower than that of Gosner stage 30 tadpoles within 72 h, recording every 12 h. The increasing temperature caused a significant increase in predation by G. affinis on P. nigromaculatus eggs and embryos. The outer jelly capsule surrounding anurans eggs might serve as a mechanical defense against predation by G. affinis due to its large diameter, relatively stationary state and unpalatability. The differences in the vulnerability of P. nigromaculatus and D. melanostictus embryos and tadpoles to G. affinis probably due to differences in the unpalatability, black skin and activity. Based on the magnitude of predation by G. affinis on the eggs, embryos and tadpoles of these two species and the combined impact of temperature, we might speculate that invasive G. affinis and global warming would have more detrimental impacts on population viability of P. nigromaculatus than D. melanostictus in China.

An unusual homing behavior found in the Sichuan Partridge during the early brooding period

In this study,we report an unusual homing behavior of the Sichuan Partridge(Arborophila rufipectus)at the Laojunshan National Nature Reserve,Sichuan Province,China.Hen Sichuan Partridges led the chicks back to the nests where they hatched in the evening and roosted there over night.This behavior lasted 6.7±4.3 nights(range=1–15;n=13)after the chicks hatched.At this stage,the hens became very vigilant to predators and human disturbance.If disturbed,they often abandoned the nests immediately and no longer returned thereafter.The ambient temperature at night during the early brooding period of Sichuan Partridge at our study site was^12.4°C.Our findings suggest that hen Sichuan Partridges may make trade-offs between nest predation risks versus the thermoregulatory needs of their young.

Responses of birds to observers holding popguns:Hunting history infuences escape behavior of urban birds

Human activities affect bird behavior both directly and indirectly.Birds constantly regulate their behavior in response to human disturbance.Gun hunting,a major directional disturbance,puts enormous selection pressure on birds.In China,gun bans have been in place for nearly 30 years,and little hunting using guns occurs in modern cities.However,little attention has been paid to whether a history of hunting still affects the behavioral adaptations of urban birds.In this study,we compared the flight initiation distance(FiD)of the Eurasian tree sparrow Passer montanus,Azure-winged magpie Cyanopica cyanus,Common hoopoe Upupa epops and Eurasian magpie Pica pica in the presence of observers with or without popguns.The Eurasian tree sparrow,Azure-winged magpie,and Eurasian magpie effectively recognized the difference between the observers,and perceived the armed observer as a greater threat,exhibiting earlier escape behavior,but this phenomenon was not found in the Common hoopoe.The different expressions in FID of experimental bird species in China cities may be affected by the different levels of recognition of huntingpressuredue todifferent hunting histories.

Gradients in predation risk in a tropical river system

The importance of predation risk as a key driver of evolutionary change is exemplified by the Northern Range in Trinidad, where research on guppies living in multiple parallel streams has pro- vided invaluable insights into the process of evolution by natural selection. Although Trinidadian guppies are now a textbook example of evolution in action, studies have generally categorized predation as a dichotomous variable, representing high or low risk. Yet, ecologists appreciate that community structure and the attendant predation risk vary substantially over space and time. Here, we use data from a longitudinal study of fish assemblages at 16 different sites in the Northern Range to quantify temporal and spatial variation in predation risk. Specifically we ask： 1） Is there evidence for a gradient in predation risk？ 2） Does the ranking of sites （by risk） change with the defi- nition of the predator community （in terms of species composition and abundance currency）, and 3） Are site rankings consistent over time？ We find compelling evidence that sites lie along a contin- uum of risk. However, site rankings along this gradient depend on how predation is quantified in terms of the species considered to be predators and the abundance currency is used. Nonetheless, for a given categorization and currency, rankings are relatively consistent over time. Our study sug- gests that consideration of predation gradients will lead to a more nuanced understanding of the role of predation risk in behavioral and evolutionary ecology. It also emphasizes the need to justify and report the definition of predation risk being used.

Human activity affects the perception of risk by mule deer

Human activity has been shown to influence how animals assess the risk of predation, but we know little about the spatial scale of such impacts. We quantified how vigilance and flight behavior in mule deer Odocoileus hemionus varied with distance from an area of concentrated human activity--a subalpine field station. An observer walked trails at various distances away from the station looking for deer. Upon encounter, the observer walked toward the focal animal and noted the distance at which it alerted and directed its attention to the approaching human （Alert Distance; AD）, and the distance at which it fled （Flight Initiation Distance;. FID）. AD and FID both increased nonlinearly with distance from the center of the field station, reaching pla- teaus around 250 m and 750 m, respectively. Deer also tended to flee by stotting or running, rather than by walking, when far from the station but they walked away when near the station. These results indicate that deer perceive lower risk near a focused area of human activity, and that vigilance and flight behaviors respond on somewhat different spatial scales. The concept of a spatial ＂human footprint＂ on behavior may be useful for understanding how human activities affect wildlife

I smell a rat： Can New Zealand birds recognize the odor of an invasive mammalian predator？

Although it is well known that birds can assess predation risk through visual and auditory cues, there has been little research into whether similar processes occur with olfactory cues. We examined the role of odor cues in assessing nest predation risk in four species of passerine birds in New Zealand. We compared the ability of two introduced European species （common starling Sturnus vulgaris and song thrush Turdus philomelos） and two native New Zealand species （rifleman Acanthisitta chloris and South Island robin Petroica australis） to respond to the scent of rat urine placed in the nest. Rats are an introduced predator in New Zealand and we expected the native birds, which did not co-evolve with any mammalian predators, to lack behavioral adaptations to the scent of rats at their nest. As expected, both riflemen and robins failed to show any change in their behavior at their nest when rat urine was present compared to a control period in which no scent was present. However, a similar lack of re- sponse was observed in the introduced song thrush; only the common starling changed its behavior in the presence of the rat urine Starlings with rat urine at the nest box were more likely to hesitate before entering and they also approached the nest, but refused to enter more often in the presence of rat scent. Both responses suggest they detected the presence of a predator and changed their behavior to minimize risk to themselves. Although based on a small number of species, our results suggest that responses to pre- dator scent may be less common in New Zealand species, and may be a factor contributing to the vulnerability of native birds to introduced mammalian predators [Current Zoology 61 （1）： 34-41, 2015].

Genetic variation in birds in relation to predation risk by hawks： A comparative analysis

The level of genetic variation among individuals may affect performance by reducing the ability of prey to detect and escape from predators if lack of genetic variation reduces flight ability directly or indirectly through reduced parasite resistance. We investigated vulnerability of common avian prey species to predation by the sparrowhawk Accipiter nisus and the goshawk A. gentilis in relation to an index of genetic similarity among adults of potential prey species. We estimated a prey vulnerability in- dex that reflects the abundance of prey relative to the expected abundance according to local population density, and related this index to band sharing coefficients based on analyses of minisatellites for adults in local breeding populations. The prey vulnera- bility index was positively correlated with the band sharing coefficient in both predators, even when controlling for potentially confounding variables. These findings indicate that prey species with high band sharing coefficients, and hence low levels of genetic variation, are more readily caught by avian predators. Therefore, predation may constitute a major cost of low levels of genetic variation in extant populations of prey [Current Zoology 61（1）： 1-9, 2015].

On the importance of concomitant conditions: Light and conspecific presence modulate prey response to predation cue

Assessment of individual costs of the anti-predator defence translating into changes in population parameters is meagre.This is because prey responses are likely to be modulated by additional factors,commonly present in the environment,but often neglected in experimental studies.To evaluate the effect of external factors on prey behavior and physiology,we exposed amphipods Dikerogammarus villosus and Gammarus jazdzewskii to the predation cue of Perca fluviatilis in different densities and light conditions.Singletons of both species exposed to the predation cue in light modified their oxygen consumption(D.villosus:reduction,G.jadzewskii:increase)compared to their respiration in predator-free conditions.However,in the presence of conspecifics or in darkness,their respiration became insensitive to the predation cue.On the other hand,the swimming activity of prey was reduced in the presence of the predation cue irrespective of prey density and light conditions,but singletons were consistently more active than groups.Thus,external factors,such as conspecifics and darkness,constantly or periodically occurring in the field,may reduce the costs of predator non-consumptive effects compared to the costs measured under laboratory conditions(in light or absence of conspecifics).Moreover,we showed that behavioral and physiological parameters of prey may change differently in response to predation risk.Thus,conclusions drawn on the basis of single defence mechanisms and/or results obtained in artificial conditions,not reflecting the environmental complexity,strongly depend on the experimental design and endpoint selection and therefore should be treated with care.

Exaggerated male pheromones in rats may increase predation cost

Male animals with more conspicuous visual and acoustic signals increase their mating success, but also increase the risk of being attacked by eavesdropping predators. In rodents, males with richer sex pheromones often have higher attractiveness to females, but whether or not the males are also at higher predation risk is poorly known. Here, we used 2 laboratory inbred strains of the rat Rattus norvegicus, Brown Norway （BN） and Lewis （LEW）, and wild-captured rats as odor donors to assess the relationship between the pheromone levels in male rats and attractiveness to domes- tic cats Felis catus. LEW rats had significantly higher levels of male pheromones （e.g., 4-heptanone, 2-heptanone, and 9-hydroxy-2-nonanone） than BN rats. Simultaneously, wild-captured male rats were selectively assigned to 2 groups （HIGH or LOW） based on pheromone content as determined by gas chromatography-mass spectrometry （GC-MS）. Binary choice tests were carried out during the night in the test room. We found that cats spent more time investigating male bedding and urine of LEW rats than the counterpart of BN rats. Likewise, cats also preferred bedding and urine odor of the HIGH wild rats compared with the counterparts of LOW wild rats. Adding synthetic ana- logs of the 3 pheromone ketones into the urine of either BN rats or LOW wild rats significantly increased their attractiveness to cats. Our data suggest that the rats with exaggerated male phero- mones more strongly attracted predators and thus as a consequence may suffer from elevated pre- dation risk.

Personalities in a crowd： What shapes the behaviour of Eurasian perch and other shoaling fishes？

Lately, there has been an increasing interest in intraspeciflc variation in behaviour, and numerous studies on persona- lity have been performed in a variety of animals, including several fish species. Individuals have been divided into coping style categories or arranged along a behaviour gradient, such as the bold/shy continuum. However, many fish species live in groups, and the social environment can influence the behaviour of an animal in different ways. There may be conflicts within groups due to competition for resources, and dominance hierarchies are commonly found. On the other hand, there are many benefits of con- sensus decision-making within the group. Conformity of behaviour is probably adaptive, due to the benefit of public information on, for example, food resources and predation risk. Accordingly, studies of fish shoals have found evidence of consensus deci- sion-making. Furthermore, factors in the environment, such as predation risk would also influence the behaviour expressed. To be able to understand behaviour patterns in a group of fish, it is necessary to consider the variation of individual characteristics, and how the group, as well as other environmental factors, affects the behaviour of individuals. Here, I will review studies on different aspects of personality within a social context in fish, with a special emphasis on the Eurasian perch Percafluviatilis [Current Zo- ology 58 （1）： 35-44, 2012].

To forage or hide？ Threat-sensitive foraging behaviour in wild, non-reproductive passerine birds

Because antipredator behaviours are costly, the threat-sensitive predator avoidance hypothesis predicts that individual animals should express predator-avoidance behaviour proportionally to the perceived threat posed by the predator. Here, we experimentally tested this hypothesis by providing wild passerine birds supplemental food （on a raised feeding platform） at either 1 or 4 m from the edge of forest cover （potential refuge）, in either the presence or absence of a nearby simulated predation threat （a sharp-shinned hawk Accipiter striatus model）. Compared with the control treatment, we observed proportionally fewer bird visits to the food patch, and the birds took longer to re-emerge from forest refuge and return to feed at the food patch, after the hawk presentation than before it. The observed threat-sensitive latency-to-return response was stronger when the food patch was further away from the nearest refuge. Overall, our results are consistent with the predictions of the threat-sensitive predator avoidance hypothesis in that wild passerine birds （primarily black-capped chickadees Poecile atricapillus） exhibited more intense antipre- dator behavioural responses with increasing level of apparent threat. The birds were thus sensitive to their local perceived threat of predation and traded-off safety from predation （by refuging） and foraging gains in open habitat in a graded, threat-sensitive manner [Current Zoology 60 （6）： 719-728, 2014].

Revealing the control of migratory fueling： An integrated approach combining laboratory and field studies in northern wheatears Oenanthe oenanthe

Migratory birds rely on fueling prior to migratory flights. Fueling in migrants is controlled by intrinsic as well as ex- trinsic factors. From captive studies we have started understanding the internal mechanisms controlling bird migration. Field studies have demonstrated the effects of external factors, such as food availability, weather, competitors, parasites or diseases, on the stopover behavior of migrants. However, an integrated approach is still missing to study coherently how the innate migration program interacts with the varying environmental cues and to estimate the contribution of the innate migration program and the environment to realized migration. The northern wheatear Oenanthe oenanthe offers a unique opportunity for integrated studies. It breeds across almost the whole Holarctic with just a ＂gap＂ between eastern Canada and Alaska. All breeding populations over- winter in sub-Saharan Africa which makes the northern wheatear one of the most long-distant migratory songbirds with extraor- dinary long non-stop flights across oceans. It is a nocturnal migrant which travels without parental or social aid/guidance. Thus, young birds rely entirely on endogenous mechanisms of timing, route selection and fueling on their first outbound migration. By establishing indoor housing under controlled conditions the endogenous control mechanisms of northern wheatear migration could be revealed. At the same time, environmental factors controlling fueling could be investigated in the field. On migration wheatears occur in a variety of habitats with sparse vegetation where their stopover behavior could be quantitatively studied in the light of ＂optimal migration＂ theory by the use of remote balances, radio-tagging and even experimentally manipulated food availability. The present paper summarizes our approach to understand the control of migration in northern wheatears by combin- ing field and laboratory studies at various spatial and temporal scales, and linking various sub-disciplines .

Competition for food in 2 populations of a wild-caught fish

Aggressive behavior when competing for resources is expected to increase as the ratio of competitors-to-resource ratio （CRR） units increases. Females are expected to be more aggressive than males when competing for food when body size is more strongly related to reproductive suc- cess in females than in males, whereas aggression is predicted to decrease under high ambient predation risk by natural selection. Under the risk allocation model, however, individuals under high ambient predation risk are expected to be more aggressive, and forage more in the absence of imminent risk than their low risk counterparts. An interaction between adult sex ratio （i.e., adult males/females）, ambient predation risk （high vs. low）, and sex on intrasexual competition for mates in Trinidadian guppies Poecilia reticulata has been shown. The interaction suggested an increase in aggression rates as CRR increased, except for males from the high predation population. To compare the patterns of competition for food versus mates, we replicated this study by using food patches. We allowed 4 male or 4 female guppies from high and low predation populations to com- pete for 5, 3, or 1 food patches. The foraging rate was higher in a high rather than low ambient pre- dation risk population. Surprisingly, CRR, sex, and population of origin had no effect on aggression rates. Despite other environmental differences between the 2 populations, the effect of ambient predation risk may be a likely explanation for differences in foraging rates. These results highlight the importance for individuals to secure food despite the cost of competition and predation.

Smaller and bolder prey snails have higher survival in staged encounters with the sea star Pisaster giganteus

Temporally consistent individual differences in behavior, also known as animal personality, can have large impacts on individual fitness. Here, we explore the degree to which individual differences in anti-predator response （or boldness） influence survival rates in groups of snails Chlorostoma funebralis when they encounter a predatory sea star Pisaster giganteus. The snail C. funebralis shows consistent individual variation in predator response where some fearful snails actively flee bodies of water occupied by predators whereas bolder snails consistently do not. We show here that bold snails are significantly more likely to survive encounters with a predatory sea star and, somewhat counterintuitively, fearful snails actually suffer higher mortality rates. We also found that smaller snails and those occurring at higher experimental densities experienced higher per capita survival rates. Positive effects of prey boldness on survival are not uncommonly reported in the animal personality literature; however, such results are inconsistent with classic animal personality theory borrowed from the optimal foraging literature. The findings herein add to the growing body of evidence that consistent individual differences in behavior can impact predator-prey interactions and that boldness is potentially under positive predator-driven selection in some systems.

Social biology of rodents

Herein, I summarize some basic components of rodent social biology. The material in this paper is summarized andcondensed from a recent book “Rodent Societies: An Ecological and Evolutionary Perspective” edited by J. O.Wolff and P. W. Sherman (2007). I describe the four basic spacing patterns and illustrate how female territoriality isa function of offspring defense and male mating tactics are a function of female defensibility. The vulnerability ofyoung to infanticide shapes female spacing and mating behavior. Food does not appear to be a defensible resourcefor rodents, except for those species that larder hoard nonperishable items such as seeds. Philopatry and theformation of kin groups result in genetic sub-structuring of the population, which in turn affects effectivepopulation size and genetic diversity. Dispersal is male biased and typically involves emigration from the maternalsite to avoid female relatives and to seek unrelated mates. Scent marking is a major form of communication and isused in reproductive competition and to assess prospective mates, but it is also eavesdropped by predators to locateprey. Females do not appear to alter the sex ratio of litters in response to maternal condition but among arvicolinerodents daughters appear to be favored in spring and sons in autumn. Rodents are relatively monomorphic;however, females tend to be larger than males in the smallest species and smaller in the larger species. Predationrisk results from an interaction among foraging time and vulnerability and in turn affects behavioral and life historycharacteristics.