Physical Health Problems and Environmental Challenges Influence Balancing Behaviour in Laying Hens

With rising public concern for animal welfare, many major food chains and restaurants are changing their policies, strictly buying their eggs from non-cage producers. However, with the additional space in these cage-free systems to perform natural behaviours and movements comes the risk of injury. We evaluated the ability to maintain balance in adult laying hens with health problems (footpad dermatitis, keel damage, poor wing feather cover; n = 15) using a series of environmental challenges and compared such abilities with those of healthy birds (n = 5). Environmental challenges consisted of visual and spatial constraints, created using a head mask, perch obstacles, and static and swaying perch states. We hypothesized that perch movement, environmental challenges, and diminished physical health would negatively impact perching performance demonstrated as balance (as measured by time spent on perch and by number of falls of the perch) and would require more exaggerated correctional movements. We measured perching stability whereby each bird underwent eight 30-second trials on a static and swaying perch: with and without disrupted vision (head mask), with and without space limitations (obstacles) and combinations thereof. Video recordings (600 Hz) and a three-axis accelerometer/gyroscope (100 Hz) were used to measure the number of jumps/falls, latencies to leave the perch, as well as magnitude and direction of both linear and rotational balance-correcting movements. Laying hens with and without physical health problems, in both challenged and unchallenged environments, managed to perch and remain off the ground. We attribute this capacity to our training of the birds. Environmental challenges and physical state had an effect on the use of accelerations and rotations to stabilize themselves on a perch. Birds with physical health problems performed a higher frequency of rotational corrections to keep the body centered over the perch, whereas, for both health categories, environmental challenges required more intense and variable movement corrections. Collectively, these results provide novel empirical support for the effectiveness of training, and highlight that overcrowding, visual constraints, and poor physical health all reduce perching performance.     

Effectiveness of Avian Predator Perch Deterrents on Electric Transmission Lines

ABSTRACT A new high-voltage transmission line in north-central Nevada, USA, was considered a potential threat to greater sage-grouse (Centrocercus urophasianus) because avian predators are attracted to and hunt from elevated perches. As a mitigation measure, perch deterrents were installed on the transmission line towers at the time of construction; in addition, 2 existing high-voltage transmission lines were retrofitted with deterrents. Previous published studies have investigated the efficacy of perch deterrents in preventing or reducing electrocution of avian predators and fecal contamination of insulators, but none have evaluated deterrents as a means of eradicating perching on towers. We conducted point transect surveys and perching-duration observations of corvids and raptors and determined that although perch deterrents did not prevent perching, the perching duration of raptors on the deterrents was reduced compared to other perching substrates. Perching of raptors indicated that some hunting most likely took place from the towers; therefore, the deterrents did not completely obviate the threat that avian predators posed to greater sage-grouse. Although the deterrents reduced the probability of avian predators perching on the towers, avian predators overcame the deterrents to take advantage of the height of the towers where no other perches of similar height existed. The perch deterrents as designed did not have the desired short-term effect on avian predators, but further monitoring may reveal longer-term effects and distinguish perching behaviors specific to different species of avian predators.     

Postural Changes Accompany Perch Location Changes in Male Butterflies (Asterocampa leilia) Engaged in Visual Mate Searching

Males of the nymphalid butterfly Asterocampa leilia perch and wait during the morning at places where females are likely to appear. Males leave their perches to court passing females and chase away intruding males. As air and ground temperatures rise during the morning, males switch from perching on the ground to perching off the ground (average height = 0.87 m) for thermoregulatory reasons. To evaluate how this switch in perch location might affect mate detection, I have investigated how the three-dimensional posture of the male's body and head varies with perch location and how conspecifics fly through male perching areas. The body posture of males varies with perch location, as measured by pitch and roll relative to gravity, and yaw relative to the sun. Moreover, the pitch and roll of the head relative to the body is adjusted in a way that compensates for variation in body pitch and roll. These results, along with information on conspecific flight altitudes, suggest that when a male is perched on the ground his visual system is positioned in such a way that he is less likely to detect conspecifics flying nearby than when he is perched off the ground. Hence, it appears that early in the morning visual detection of mates and intruding males may be compromised by thermoregulatory concerns.     

Individual differences in reinforcing effects of song

Six out of eight first-year male chaffinches showed some reinforcing effect of song, by perching on a particular perch and remaining on it in order to keep song playing. Since birds could show reinforcing effects by changing frequency, duration, or both, of operant perching, five different indices of reinforcement were considered. Correlations between all but one pair of indices were low, and no index had higher values than any other. For some individuals, one index was high, and for others another. Thus the need for recognizing, rather than ignoring, individual differences is illustrated.     

Effects of copper on growth and starvation in perch, Percafluviatilis L.

Non-fed perch and perch fed a reduced ration were exposed to copper (0.15 of the 96-h LC50) for 40 days. Starvation and growth rates were determined at 5-day intervals to estimate the copper's effects on metabolism and food consumption. In general, copper increased starvation rates, reduced growth rates but did not affect food consumption. Weight reductions occurred in the first, but not in the second, 5-day interval. There then followed an accelerated and linear weight reduction for 10–15 days, after which the rate of weight reduction was constant and at its highest level. Thus, perch did not acclimatize but a steady state of high metabolic cost was indicated over the last 20 days. The establishment and maintenance of this steady state was attributed to a detoxification mechanism. The increase in metabolic rate was, at steady state, estimated to increase the standard metabolic rate by at least 1.8 times. There was no apparent increase in specific dynamic action but increased activity due to an increase in competition for food was estimated to further increase the metabolic rate by 1.2 times.     

Hawk Eyes II: Diurnal Raptors Differ in Head Movement Strategies When Scanning from Perches

Background

Relatively little is known about the degree of inter-specific variability in visual scanning strategies in species with laterally placed eyes (e.g., birds). This is relevant because many species detect prey while perching; therefore, head movement behavior may be an indicator of prey detection rate, a central parameter in foraging models. We studied head movement strategies in three diurnal raptors belonging to the Accipitridae and Falconidae families.

Methodology/Principal Findings

We used behavioral recording of individuals under field and captive conditions to calculate the rate of two types of head movements and the interval between consecutive head movements. Cooper''s Hawks had the highest rate of regular head movements, which can facilitate tracking prey items in the visually cluttered environment they inhabit (e.g., forested habitats). On the other hand, Red-tailed Hawks showed long intervals between consecutive head movements, which is consistent with prey searching in less visually obstructed environments (e.g., open habitats) and with detecting prey movement from a distance with their central foveae. Finally, American Kestrels have the highest rates of translational head movements (vertical or frontal displacements of the head keeping the bill in the same direction), which have been associated with depth perception through motion parallax. Higher translational head movement rates may be a strategy to compensate for the reduced degree of eye movement of this species.

Conclusions

Cooper''s Hawks, Red-tailed Hawks, and American Kestrels use both regular and translational head movements, but to different extents. We conclude that these diurnal raptors have species-specific strategies to gather visual information while perching. These strategies may optimize prey search and detection with different visual systems in habitat types with different degrees of visual obstruction.     

Auditory prey location in a pause--travel predator: search height, search time, and attack range of Tengmalm's owls (Aegolius funereus)

We studied the nocturnal hunting and diurnal roosting behaviorof 17 radio-equipped Tengmalm's owls (Aegolius funereus), 12males and 5 females, in coniferous forest during their nestingseason. The owls perched lower when hunting than when roosting,probably because hunting perches were selected to minimize thepredator-prey distance or to obtain unobstructed access to theground-dwelling small mammal prey, whereas roosting percheswere selected to minimize the probability of being detectedby an avian predator. There was no difference between perchingheights associated with giving up and prey attack, nor werethere any differences between perching heights, perching times,and attack distances associated with successful and unsuccessfulattacks. There were no sexual differences in perching heightduring hunting or roosting. However, giving-up times tendedto be longer for females than for their mates, which is expectedbecause females are larger than males, and the relative costof flight increases with body mass. The instantaneous attackrate was independent of perching time. The owls gave up theirperches at a constant rate and independently of the amount oftime already spent on the perch in an exponentially decayingpattern. The owls perched longer, however, before launchingan attack than before giving up, probably in order to observedetected prey until the right moment for an attack. Attack distancewas independent of both perching height and perching time. Perchingtime was inversely related to perching height, which fits thetheoretical expectation that the search area will decrease withincreasing height in birds that locate prey auditorily.     

Why do some nectar foragers perch and others hover while probing flowers?

Diurnal hawkmoths, Hemaris fuciformis, and bumblebees, Bombus pasquorum, were observed foraging for nectar in flowers of Viscaria vulgaris. The hawkmoths hovered in front of the flowers, while the bees perched on them. The hawkmoths had a faster probing rate than the bees, and consequently also had higher gross and net rates of energy gain. A model is presented that shows that hovering only yields a higher net rate of energy gain (NREG) than perching when nectar volumes are high due to low competition for the resource. The difference in NREG of perchers and hoverers decreases with an increase of competition, and eventually perching yields the highest NREG. This is an effect of the higher cost of hovering. The results suggest that hovering can only evolve as a pure evolutionarily stable strategy (ESS) if competition is reduced, for example by co-evolutionary specializations with plants. The possibility that it has evolved as a mixed ESS (i.e. individuals can both hover and perch depending on the resource level) is discussed. The evolution of optimal foraging strategies is discussed, and it is pointed out that the rate of gain of an animal is independent of the strategy used when all competing foragers use the same strategy, but competitively superior strategies will nevertheless evolve because they are ESSs. Competition between strategies with different energy costs are special, because resource availability determines which strategy is competitively superior. A high-cost strategy can only evolve as a pure ESS at high resource levels, or as a mixed ESS at intermediate levels.     

Night-time roosting in laying hens and the effect of thwarting access to perches

Free-living hens roost on branches in trees at night, and laying hens in aviary systems or cages provided with perches also make extensive use of these for night-time roosting. It is therefore suggested that roosting on perches is important to the hens and that domestic hens should be provided with perches in order to promote welfare. However, no study has addressed the question of motivation for roosting. In the present experiment, we studied undisturbed roosting behaviour and the reaction of commercial laying hens when roosting on perches was thwarted. Fifty-two adult hens (Lohmann Selected Leghorn, LSL) were kept in two groups of 26 hens in litter pens with perches at heights of 23, 43 and 63 cm. Behaviour was observed for 60 min starting at lights-off, registering the number of hens on each perch level. The hens started to get onto the perch immediately and within 10 min after lights-off, more than 90% of the hens were on the perch. All hens roosted close together on the top perch. In a second experiment, 24 hens were kept in eight groups of three birds each in experimental pens equipped with perches. Birds were tested in four different situations: (1) the pen unchanged (Base), (2) the perch covered with plexiglass (PCov), (3) the perch removed (PRem) and (4) the unchanged pen (Post). The order of PCov and PRem alternated between groups in a balanced manner and all groups of birds experienced all four treatments. The hens were observed for 60 min from lights-off using focal sampling. For comparisons, the Post treatment served as the control. In the treatments where perching was not possible, the hens spent less time sitting (p=0.042), and also tended to spend more time standing (p=0.06), than in the control. Furthermore, the hens moved more (p=0.042) when the perch was inaccessible, and when the perch was visible but inaccessible they also showed more attempts to take off (p=0.042). These findings can be interpreted as increased frustration and/or exploration, probably to find an alternative roosting site. Together with the high use of perches for night-time roosting under undisturbed conditions, these results indicate that laying hens are motivated to perch and imply that hens kept under conditions where perching is not possible may experience reduced welfare.     

Bird-Flowers: Hovering Versus Perching Exploitation

Usually, bird-flowers are classified into New World flowers (used by hovering hummingbirds) and Old World species (adapted to perching birds). Since there are many observations which violate this classification the proposal is made to distinguish between blossoms adapted to hovering birds and those providing a well-defined perch. Characters and examples are given for both groups including the different ways a perch is provided by the plant and the distinct methods of hover-flight in birds. The diverse adaptive solutions for bird pollination within some taxa are exemplified. To understand bird-flowers the actual functioning of flowers must be in focus, and not the geographic distribution nor the systematic affiliation of their visitors.     

Effects of density on perching behavior of broiler chickens

Exercise through perching has been suggested as a way to reduce the impact of leg problems in broiler chickens. It is possible that higher stocking densities may motivate birds to perch more, and perhaps reduce some of the detrimental effects to broiler health seen with high stocking densities. The goal of this research was to investigate the effects of density (10, 15, and 20birds/m(2)) and perch design on the frequency of perch utilization. Mixed sex broilers were assigned to 36 pens in a four perch treatmentxthree density factorial with three replications for each treatment/density combination in a randomized complete block design. Pens were assigned to one of four perch treatments: control (no perches), horizontal (three horizontal perches), angled (three 10 degrees angled perches), or mixed angle (one horizontal, one 10 degrees angled, and one 20 degrees angled perch), at each of the three densities. The results show that although the frequency of perch use was low, (2.6%+/-0.15), significant preferences were clear. Perching frequency was significantly higher when birds were raised at stocking densities of 15 (2.88+/-0.303) or 20birds/m(2) (2.76+/-0.211), as opposed to 10birds/m(2) (2.10+/-0.209) as indicated by a marginally significant main effect (p<0.0597), and a significant linear effect (P<0.0427). The birds used the horizontal perches the most, followed by 10 degrees angled and mixed angle perch treatments with decreasing frequency. An effect of age was found, in that perching increased during the first 4 weeks, and dropped off significantly at the end of the rearing period for all perch treatments. In general, perches closest to the hallway or outside of the house were used more than perches in the middle of the pen. Preferential use of the highest section of the 10 degrees angled perches was also found. The applied perch treatments or densities did not significantly affect final body weight or feed conversion. Percent mortality due to heat stress showed a significant increase with density, while mortality not caused by heat stress did not change with perch treatment or density.     

The influence of simulated aquatic macrophytes on the zooplankton consumption rate of juvenile roach, Rutilus rutilus, rudd, Scardinius erythrophthalmus, and perch, Perca fluviatilis

Laboratory experiments showed that, of zooplanktivorous roach, rudd and perch, in the absence of any environmental structure roach were the most efficient feeders, but high densities of simulated submerged marcrophytes elevated perch to this position; rudd matched the performances of perch and roach only at intermediate structure densities. These changes in efficiency rankings with increased structure were the result of overall decreases in the performances of roach and rudd. Simulated water lilies and emergent reeds had their own influences on consumption rate. These effects were largely mediated through relationships between structure density and swimming speed; roach and rudd, not perch, showed reduced swimming speeds in the more structured environments. Observations of the routine behaviour of the fish suggest that their assessment of predation risk may be an important factor in determining their activity level and hence foraging strategy.     

Behavioral and physiological thermoregulation in male cicada killers (Sphecius speciosus) during territorial behavior

(1) Male cicada killers had elevated, apparently regulated, thoracic and head temperatures during territorial perching and patrolling in full sunshine. (2) Dead, dry wasps reached near-lethal temperatures on the bare ground, and were hotter with their bodies perpendicular to the sun's rays, as opposed to parallel. (3) The percentage of males perching on the ground, their perch duration, and the percentage oriented perpendicular to the sun decreased during the mid-day. (4) Males used a low-amplitude wing vibration early and late in the day, perhaps boosting heat production. (5) Changes in behavior were related to changes in the intensity of solar radiation.     

Avian electrocution rates associated with density of active small mammal holes and power-pole mitigation: Implications for the conservation of Threatened raptors in Mongolia

Avian electrocution at power lines is a well-documented phenomenon, yet factors influencing the frequency of electrocution events and the efficacy of mitigation techniques remain relatively under-reported. During May-July, we surveyed a 56 km long 15 kV electricity distribution line running across open steppe in Mongolia recording electrocuted birds of prey under the power poles. We recorded high rates of electrocution of several Threatened raptor species, particularly the Endangered Saker Falcon Falco cherrug, which was killed at a monthly rate of 1.6 birds per 10 km during the period of our study. Electrocution frequency at line poles was associated with density of small mammal holes and the deployment of mitigation measures. It is likely that local prey abundance influences the frequency of birds of prey perching on power poles, which is consequently reflected in electrocution rate. We evaluated the efficacy of mitigation measures and found that the use of perch deflector spikes on the crossarms of line poles reduced electrocution rates when 3 or 4 spikes were deployed. Perch deflectors probably worked by reducing the opportunity for birds to perch adjacent to pin insulators rather than by reducing the frequency of birds perching on the crossarm per se. At anchor poles, reconfiguration of jump wires at two phases, so they passed under the crossarm rather than over, significantly reduced electrocution rates. These mitigation measures potentially represent a relatively inexpensive method to reduce the frequency of raptor electrocution events in regions where cost is a key factor for power line managers in determining whether or not any form of mitigation is used.     

桃红颈天牛成虫的交配行为及对不同寄主植物的栖落和产卵选择性

【目的】桃红颈天牛Aromia bungii是一种钻蛀性害虫,主要以蔷薇科果树和观赏树木为寄主。本研究旨在搞清楚桃红颈天牛成虫的交配产卵行为及其对不同寄主植物的栖落和产卵选择性。【方法】选择苹果Malus pumila、山樱花Prunus serrulata var. spontanea、桃Prunus persica、西府海棠Malus micromalus、毛樱桃Prunus tomentosa、秋子梨Pyrus ussuriensis、杏Prunus armeniaca和红叶李Prunus cerasifera var. atropurea 8种寄主植物木段,构建为成虫的活动场所,观察桃红颈天牛成虫的交配和产卵行为,并测定桃红颈天牛成虫在不同寄主木段上的栖落数量和产卵量。【结果】桃红颈天牛成虫的交配行为分为避让、打斗和交配3种行为。交配过程可分为相遇抱对、插入输精、交配后陪护3个阶段。桃红颈天牛雌虫产卵时无刻槽行为,喜欢将卵产于较为狭窄的缝隙中。雌虫偏好在桃树木段上栖落,雄虫则偏好在毛樱桃木段上栖落。李亚科李属的桃是桃红颈天牛最喜欢的产卵寄主木段,而雌虫在苹果亚科的苹果、海棠和秋子梨木段上产卵极少。相关性分析结果表明雌虫在寄主木段上的栖落数量与产卵量占比间存在正相关性,雄虫在寄主木段上的栖落数量与雌虫在寄主木段上的栖落数量之间也存在正相关性。【结论】桃红颈天牛雌成虫最喜欢桃树木段,雄虫对寄主植物的选择性与雌虫并不完全相同。     

Raptor and Corvid Response to Power Distribution Line Perch Deterrents in Utah

Abstract: Increased raptor and corvid abundance has been documented in landscapes fragmented by man-made structures, such as fence posts and power lines. These vertical structures may enhance raptor and corvid foraging and predation efficiency because of increased availability of perch, nesting, and roosting sites. Concomitantly, vertical structures, in particular power distribution lines, have been identified as a threat to sage-grouse (Centrocercus spp.) conservation. To mitigate potential impacts of power distribution lines on sage-grouse and other avian species, the electrical power industry has retrofitted support poles with perch deterrents to discourage raptor and corvid use. No published information is available regarding efficacy of contemporary perch deterrents on avian predator use of lower-voltage power distribution lines. We evaluated efficacy of 5 perch deterrents mounted on support poles of an 11-km section of a 12.5-kV distribution line that bisected occupied Gunnison sage-grouse (Centrocercus minimus) habitat in southeastern Utah, USA. Perch deterrents were mounted on the line in November–December 2006 following a random replicated block design that included controls. During 168 hours and 84 hours of direct observation in 2007 and 2008, respectively, we recorded 276 and 139 perching events of 7 potential avian predators of sage-grouse. Golden eagles (Aquila chrysaetos) were the dominant species we recorded during both years. We did not detect any difference in perching events by perch deterrent we evaluated and controls (P > 0.05). Perch deterrents we evaluated were not effective because of inherent design and placement flaws. Additionally, previous pole modifications that mitigated avian electrocutions provided alternative perches. We did not record any raptor or corvid electrocutions or direct predation on Gunnison sage-grouse. The conclusions of this study can be applied by conservation groups and power companies to future management of power distribution lines within areas inhabited by species sensitive to man-made vertical structures.     

Perch selection in Sympetrum species (Odonata: Libellulidae): importance of vegetation structure and composition

1. Perching dragonflies are closely associated with the physical structure of vegetation because adults utilise plants when foraging, thermoregulating, and mate-seeking. However, little attention has been given to which structural attribute of vegetation is playing a key role within foraging habitat use. 2. This study focused on the influence of different features of perches on their selection by adult dragonflies. As a model group, a typical percher behavioural guild of Sympetrum was used and experimental plots with artificial perches and different structural properties were established. 3. It was found that adults preferred perch sticks with a wider diameter and larger spacing. It is assumed that these perching sites are advantageous because their base is more stable, they provide the best view for successful foraging, and there is no interference among individuals. 4. This study also revealed significant differences between male and female preferences. Females used less structured vegetation formed by thin perches in high densities. It is suggested that female discrimination is influenced by the higher competitiveness of males, which is related to their agonistic behaviour. 5. These results suggest that the availability of perches in the foraging habitat might be an essential requirement for adults. However, within the terrestrial surroundings of breeding sites, the structure of vegetation providing conditions for perching may be associated only with certain habitats. In intensive landscapes, physically structured vegetation can be limited or completely absent.     

Foraging area and hunting technique selection of Common Kestrel (Falco tinnunculus) in winter: the role of perch sites

In winter, Common Kestrel minimizes energy expenditure by using the low-cost, low-profit technique of perch hunting. Existence of the perch sites is the precondition of perch hunting. Therefore, one can predict that the kestrels would prefer a habitat with more perch sites, and perch sites should have an important role in the kestrels' hunting technique use, habitat selection and habitat use in winter. To test this prediction, the authors manipulated two areas in a grassland. They increased the potential perch sites in one area with bamboo poles (hereafter test area) and kept another as control (hereafter control area). They observed and compared the kestrels' use and their behaviors in these two areas. Far more kestrels appearing in the test area with increasing perch sites than in the control area were recorded. The kestrels stayed in the test area with more perch sites significantly longer than in the control area. And in the test area with more perch sites, kestrels hunted 77.24% of the total hunting with the technique of perch hunting. In the control area, kestrels hunted only with the technique of flight-hunting. There was a significant correlation between the technique used by kestrels and the areas with or without perch sites. In the test area with increasing perch sites kestrels spent 51.8% of their time in perching and 12.1% in air, which were 30.1% and 34.8%, respectively, in the control area. There was no significant difference in hunting profit between areas. The results suggest that perch sites play an important role in the selection of hunting technique and foraging habitat for kestrels in winter, and kestrels appear to prefer the habitat with suitable perch sites in winter.     

栖木在越冬红隼（Falco tinnunculus）的觅食地与捕食方式选择中的作用

栖木是重要的生境因子,对于鸟类生境选择和利用具有重要意义。2003年9月-2004年3月,采用固定样地对照观测的方法,分析研究栖木在越冬红隼（Falco tinnunculus）的栖息地选择与捕食方式选择中的作用。研究结果表明,增加了栖木的试验区（下称试验区）,红隼的出现频率远大于未增加栖木的对照区（下称对照区）;试验区红隼个体平均停留时间显著长于对照区;在试验区红隼栖停捕食占捕食次数的77.24%,而在对照区红隼只进行飞行捕食,红隼捕食方式和样地中是否增加栖木具有极显著相关性;试验区,红隼栖停行为时间占51.8%,大于对照区（30.1%）,对照区中,红隼在空中的行为如飞行、翱翔、悬停等行为时间所占比例为34.8%,远高于试验区（12.1%）。这些结果表明,栖木在越冬红隼的栖息地选择和捕食方式选择中具有重要的作用,栖木的存在是栖停捕食的先决条件,冬季红隼偏好于具有较好栖木条件的栖息地,并且偏向于采取低消耗低收益的栖停捕食。     

Adult Male Density Influences Juvenile Microhabitat Use in a Territorial Lizard

Habitat choice often has strong effects on performance and fitness. For many animals, optimal habitats differ across age or size classes, and individuals shift habitat use through ontogeny. Although many studies document ontogenetic habitat shifts for various taxa, most are observational and do not identify the causal factor of size‐specific habitat variation. Field observations of the brown anole lizard (Anolis sagrei) show that juveniles perch on shorter and thinner vegetation than adults. We hypothesized that this variation is due to adult males forcing smaller juveniles to less preferred habitat. To test this assertion, we manipulated adult male densities in mesh enclosures with artificial trees to examine the response of juvenile microhabitat choice. We found that adult male density had strong effects on juvenile perch height, perch width, and substrate use, suggesting that age‐class competition contributes to the observed ontogenetic differences in habitat choice. We also found that time of day significantly affected juvenile perch height and substrate use. In many cases, our results suggest that juveniles distance themselves from adults using different microhabitats from those used in our control ‘no‐adult’ treatment. However, these findings were often body size dependent and varied depending upon time of day. This study highlights the complexity of juvenile perching behavior and demonstrates the role of intraspecific interactions in shaping habitat use by juvenile animals.