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Measuring activity of small mammals in the field is challenging because they are often out of view. We used a novel method, based on temperatures of collar radio transmitters, to quantify the proportion of time eastern chipmunks (Tamias striatus (L., 1758)) spent active, curled up resting, and torpid during the summer and fall of 2 years in southern Quebec. Time active over the 24 h day was lower in a nonmast (8%) than a mast (26%) year. In the mast year, activity varied strongly from a low of 7% during the summer lull to a high of 35% in the fall. Chipmunks that exploited a feeder had higher activity (33%) than chipmunks that did not (19%). Activity was higher during the day, but some activity occurred at night. Daily activity patterns varied strongly among seasonal periods. There was no evidence of torpor during the summer lull. Torpor started much earlier in the nonmast than in the mast year and occurred more at night than during the day. Overall, our study suggests that activity in this food-storing hibernator is positively influenced by food availability and indicates that thermosensitive radiotelemetry is a promising method for recording continuous activity.

Summary 1. Populations experiencing localized mortality can recover in the short term by net movement of individuals from adjacent areas, a process called compensatory immigration or spillover. Little is known about the factors influencing the magnitude of compensatory immigration or its impact on source populations. Such information is important for understanding metapopulation dynamics, the use of protected areas for conservation, management of exploited populations and pest control. 2. Using two small, territorial damselfish species (Stegastes diencaeus and S. adustus) in their naturally fragmented habitat, we quantified compensatory immigration in response to localized mortality, assessed its impact on adjacent source populations and examined the importance of potential immigrants, habitat quality and landscape connectivity as limiting factors. On seven experimental sites, we repeatedly removed 15% of the initial population size until none remained and immigration ceased. 3. Immigrants replaced 16–72% of original residents in S. diencaeus and 0–69% in S. adustus. The proportion of the source population that immigrated into depleted areas varied from 9% to 61% in S. diencaeus and from 3% to 21% in S. adustus. In S. diencaeus, compensatory immigration was strongly affected by habitat quality, to a lesser extent by the abundance of potential immigrants and not by landscape connectivity. In S. adustus, immigration was strongly affected by the density of potential migrants and not by habitat quality and landscape connectivity. On two control sites, immigration in the absence of creation of vacancies was extremely rare. 4. Immigration occurred in response to localized mortality and was therefore compensatory. It was highly variable, sometimes producing substantial impacts on both depleted and source populations. The magnitude of compensatory immigration was influenced primarily by the availability of immigrants and by the potential improvement in territory quality that they could achieve by immigrating and not by their ability to reach the depleted area.

There has been surprisingly little attention to adaptive variation in the locomotor speed and gaits used in antipredator behaviour. We investigated the relationship between body size and the use of two alternative gaits by three species of parrotfishes (princess, Scarus taeniopterus; queen, Scarus vetula; stoplight, Sparisoma viride) escaping an approaching snorkeller in their natural fringing reef habitat in Barbados. As body size increased from about 7 to 58 cm, the proportion of fish using an energetically more costly but relatively faster escape (body and caudal fin swimming) rather than a less costly and relatively slower escape (paired fin swimming) decreased from 100% to 0%. In contrast, the study confirmed previous research showing that larger fish fled at greater distances from the snorkellers, behaviour which would have increased safety but incurred higher opportunity costs. We conclude that small fish require a more expensive gait to attain an adequate escape speed. Thus, the gait used for escaping shows a compensatory relationship with body size because small individuals with lower swimming capacity use a higher proportion of that capacity. On the other hand, flight initiation distance shows cospecialization with body size because larger fish with higher swimming capacity further reduce their risk by fleeing sooner.

Most wild animals show direct negative responses to human disturbance; however, disturbance may also have positive indirect effects by altering species interactions. In the Caribbean, introduced mongooses (Herpestes javanicus) are an important diurnal predator of the nests of critically endangered hawksbill sea turtles (Eretmochelys imbricata). We asked whether daytime visitor activity could benefit hawksbills by reducing mongoose activity in nesting habitat. We used track monitoring sites to measure how mongooses alter their space use in response to fluctuating human beach use and availability of hawksbill nests, and we estimated the indirect impact of human disturbance on nest predation for 5 years of hawksbill nesting. Human activity substantially decreased mongoose use of nesting habitat. Mongoose activity increased with abundance of nests and was lower at the edge than the interior of patches of beach vegetation, but neither factor altered relative sensitivity to disturbance. We estimated that, in addition to deterring mongooses from accessing nests on the open beach, human activity has the potential to reduce predation of nests in vegetation by up to 56% at our site, with the greatest per capita impact at low (

Flight initiation distance (FID), the distance at which an organism begins to flee an approaching threat, is an important component of antipredator behavior and a potential indicator of an animal’s perception of threat. In a field study on parrotfishes, we tested the predictions that FID in response to a diver will increase with body size, a correlate of reproductive value, and with experience of threat from humans. We studied a broad size range in four species on fringing reefs inside and outside the Barbados Marine Reserve. We used the Akaike's Information Criterion modified for small sample sizes (AICc) and model averaging to select and assess alternative models. Body size, reserve protection, and distance to a refuge, but not species, had strong support in explaining FID. FID increased with body size and generally remained two to ten times fish total length. FID was greater outside the reserve, especially in larger fish. Although we were not able to completely rule out other effects of size or reserve, this study supports predictions of an increase in FID with reproductive value and threat from humans.

Studies of coral reef fish recruitment have focused more on factors influencing the return of larvae to reefs and the process of settlement than on factors affecting survival in the plank- ton, despite the well-documented importance of the larval environment for temperate marine spe- cies. We examined the ability of environmental factors to explain temporal patterns of recruitment in 8 taxa of coral reef fishes, distinguishing variables associated with settlement from those associated with the pelagic larval stage. At 10 d intervals over a 17 mo period, we collected newly settled fishes from settlement units in Barbados (West Indies). We collected concurrent data on 3 settlement- associated variables, lunar darkness, wind speed, and tidal amplitude, and 5 larval environment vari- ables, sea-surface temperature, cloud cover, salinity, chlorophyll a concentration, and normalized water-leaving radiance at 555 nm. The last 3 were associated with low-salinity intrusions originating in the Amazon. We used hierarchical partitioning and Mallow's C(p) model selection to identify important variables for each taxon. Temporal patterns of recruitment differed among taxa of which 6 showed significant environmental correlations. Significant settlement variables included lunar darkness and tidal amplitude. Significant larval environment variables were diverse and varied in magnitude and sign across taxa. The effects of larval variables were generally strong relative to settlement variables. The temporal scale of the strongest environmental predictor differed across taxa. Our study supports the views that planktonic factors affecting larval survival substantially influ- ence recruitment in coral reef fishes and that different species are affected differently by a common, temporally variable, planktonic environment.

Predators are an important source of mortality for animals that lay their eggs in buried nests. We asked how depth alters the process of predation for buried prey. We outlined a general model of predation risk where depth may alter both prey detection and subsequent capture: deeper prey are detected less often because the strength of olfactory cues decreases with burial depth and, once detected, are further protected by the costs of digging. Using this framework, we examined how burial depth influenced egg predation for critically endangered hawksbill sea turtles (Eretmochelys imbricata) by introduced mongooses (Herpestes javanicus) in Barbados. We tested the effects of nest depth on detection and subsequent predation using observational data on hawksbill nests over a 2-year period and an experiment with artificial nests. For both real and artificial nests, depth had little effect on nest detection by mongooses, but once detected, shallower nests were much more likely to be preyed on. Mongooses appear to use depth-invariant surface cues to detect nests but increase digging persistence in response to olfactory cues. We argue that excavation cost is an important but overlooked mechanism protecting deeply buried resources. For reptiles with buried nests, the relationship between depth and predation risk leads to important predictions about how changes to nesting habitat or the predator community will affect egg survival and offspring sex ratio. More generally, identifying the mechanisms by which burial depth protects prey is essential for understanding how resource burial strategies evolved and are maintained in predator‐prey systems. Key words: cache recovery, conservation, hatching success, Herpestes auropunctatus javanicus, invasive species, temperature-dependent sex determination. [Behav Ecol]

When food patch quality varies unpredictably over time, animals may benefit from sampling to track these changes. Previous theoretical work has shown how patch and environmental characteristics influence the optimal sampling policy, but there has been little attention to the effects of conspecifics, especially for species that do not live in groups. We used a simulation model to investigate the influence of conspecifics, as both competitors and providers of social information, on the optimal sampling behaviour of nongroup foragers. Competition reduces the range of patch characteristics for which frequent sampling provides a higher gain rate than rare or no sampling. Under conditions where sampling is beneficial, however, competition has little effect on the optimal sampling rate. Social information generally decreases the optimal sampling rate. However, the effect is small when the social information is unreliable. This will often occur when animals forage solitarily because of an inability to detect other animals at the patch or to distinguish animals that are sampling the patch from those that are exploiting it. Thus, the presence of conspecifics should reduce the sampling rate of nongroup foraging animals, but the extent of the reduction will depend on the reliability of the available social information.

Foraging and vigilance conflict in animals that lower their head during food search and handling, but it is less clear whether these activities conflict in animals that handle food with the head raised. In these species, at least part of the foraging process is physically compatible with vigilance. Nevertheless, both vigilance and food handling require cognitive resources, so animals may not be vigilant whenever their head is raised. We tested whether grey squirrels are vigilant when they are handling food items held in their forepaws while in a semiupright posture. If vigilance occurs during handling, we predicted that squirrels finding food in a location with a partially blocked view would change location before handling to improve visibility. Because this test assumes that the benefit of vigilance during handling is greater than the cost of moving, we tested small food items (sunflower seeds) in which the temporal cost of changing position on the rate of food intake was relatively high and large items (crackers with peanut butter) in which the cost of changing position was relatively low. When handling crackers, squirrels that had their lateral view obstructed at the food presentation site changed to a position with a better view more often than controls or squirrels that had their overhead view obstructed. When handling sunflower seeds, squirrels never changed their position. These results support the view that squirrels are vigilant during semiupright handling, but that vigilance may be sacrificed if it leads to high foraging costs.

When food patches vary in quality over time, sampling by repeated visits can allow animals to track this variation and improve their foraging success. Sampling, however, requires spending time visiting patches that are currently poor. The optimal investment in sampling should depend on characteristics of the patch, the animal, and the environment, but there are few empirical studies of these relationships in nature. Here, we describe discovery, exploitation, and sampling of randomly varying artificial food patches by free-ranging eastern chipmunks ( Tamias striatus (L., 1758)). Chipmunks effectively tracked variation over a broad time scale, discovering patches within a few days, sampling and exploiting over several weeks, and decreasing sampling when renewals ceased. Sampling allowed the chipmunks to track variation on an hourly scale through rapid discovery of renewals. Sampling rates were high (median = 0.3 visits·individual–1·h–1; range = 0–4.2). Sampling was not affected by the frequency or magnitude of patch renewal but was lower for chipmunks whose burrows were farther from the patch. Sampling is an important part of chipmunk foraging strategy, but the difficulty of estimating patch quality and renewal rate and the effects of competition may prevent a close matching between sampling rate and patch characteristics under natural conditions.

When an animal has found and consumed food at a new location, information about whether and when food will be present again could improve future foraging efficiency. A series of rapid returns followed by less frequent visits and finally abandonment of the patch could provide such information. By analogy with area-concentrated (area-restricted) search, we call this hypothesized pattern “time-concentrated sampling”. We tested whether eastern chipmunks ( Tamias striatus (L., 1758)) would show time-concentrated sampling in the field and whether the pattern of visits would be affected by patch value. We used peanuts to induce animals to discover a small patch of sunflower seeds. After depleting the patch, returning to find it empty, and leaving without food, 36 of 40 animals returned on sampling visits. Sampling rate was initially high and declined over 4 h. The number of peanuts and number of visits where seeds were obtained positively predicted sampling rate, but the volume of sunflower seeds presented and the distance to the burrow did not. We conclude that chipmunks exhibit flexible time-concentrated sampling.

We developed a benthic standard monitoring unit for recruitment of fishes (SMURF) to sample fishes that settle in coral rubble and tested it on three fringing reefs on the west coast of Barbados, West Indies. These rubble SMURFs are inexpensive to construct and permit newly settled fishes, including cryptic, secretive and small species, to be quickly and fairly completely (> 83%) removed by divers without returning the unit to the surface. Over a 3-month period involving 9 collections, 32 units on 3 reefs yielded 948 newly settled fishes belonging to 28 taxa (3.3 ± 0.2 S.E. recruits per sample, n = 287) in addition to numerous crustaceans. Most specimens were Sparisoma spp. (Scaridae) (41.8%) and Stegastes partitus (Pomacentridae) (13.6%), with moderate numbers of Scarus spp. (Scaridae) (8.6%), Lythrypnus spp. (Gobiidae) (7.4%), and Pseudogramma gregoryi (Serranidae) (7.2%). Sampling SMURFs at 1-day rather than 11-day intervals yielded approximately twice as many fish, although some taxa were not affected by sampling frequency, indicating taxon-specific differences in post-settlement loss rates. Netting, intended to reduce predation on settlers, did not affect settlement estimates unless algae grew on it, suggesting that the SMURF design minimizes fish predation even in the absence of the netting. Over time, however, the netting resulted in substantial algal growth that was associated with an increase in abundance of Sparisoma spp. and a decrease in the abundance of S. partitus . This suggests that settler estimates are more affected by microhabitat changes from algal growth than by predation. During low settlement periods, SMURFs performed better than light-traps in assessing the daily input of new settlers of two abundant taxa. Eight SMURFs per reef were sufficient to demonstrate differences in settlement rates and temporal correlations in settlement within and among reefs. This study underscores the potential of benthic SMURFs to measure settlement of coral reef fishes at a range of spatio-temporal scales with moderate research cost and effort, and to facilitate the study of the settlement stage of several taxa.

When territory owners temporarily leave their territories, intrusion often increases. Periodic returns (revisits) may reduce intrusion, but not necessarily, because this tactic might increase total time away from the territory. The effectiveness of revisits also depends on a subsequent delay in the return of intruders. Adult female yellowtail damselfish briefly leave their territories in the early morning every 3 days to spawn. Some females make a single trip; others return to their territory several times before they finish spawning. To determine how much time females spent on revisits and whether it reduced intrusion, we observed revisits by multiple-trip females and compared intrusion on the territories of spawning and experimentally caged single-trip and multiple-trip females. If revisits reduce intrusions, multiple-trip females should have higher intrusions when caged than when spawning. If revisits show adaptive plasticity, caged single-trip females should have lower intrusion rates than caged multiple-trip females. Not counting the first trip to the male's nest and the final return trip, we estimated that spawning multiple-trip females averaged 86% of their time at the male's nest, 11% back in the territory and 3% travelling. When owners were spawning, territories of both single- and multiple-trip fish received about 5–7 min of intrusion. When owners were caged, intrusion increased significantly only on territories of multiple-trip females. We consider this the first direct evidence that revisits during temporary absences reduce intrusion on territories, suggesting that revisiting is a plastic trait that females may vary in response to intruder pressure.

We developed a modified visual census technique suitable for fairly sedentary, hole-dwelling species and used it to determine the diversity, density, biomass, and habitat use of morays at four sites including fringing, patch, and bank reefs in Barbados, West Indies. The method involved a careful search during two passages over transects by day and by night, noting size and position of morays seen, and using the number of new observations on the second passage to estimate the proportion of morays not seen. First passage counts were generally higher than numbers of morays recorded in previous visual censuses. These estimates were raised when we used the time period (day or night) with the highest average density visible for each species, added different individuals from the two passages, and corrected for individuals not seen. We saw more goldentail morays (Gymnothorax miliaris) during the day but more spotted (G. moringa), viper (Enchelycore nigricans), and chestnut (E. carychroa) morays at night. Counts of chain morays (Echidna catenata) did not differ significantly between night and day. Relative abundance and size of moray species varied among sites and to a lesser extent among habitat types within sites, but spotted morays were generally the most important in numbers and biomass. Mean estimated moray density and biomass were much higher than in most previous visual censuses, but similar to rotenone samples on other reefs and comparable to those of other families of predatory fishes. Our findings confirm that morays are abundant and potentially important predators that should be the focus of more attention in ecological studies of coral reefs.

We examined the abundance of blue tang surgeonfish, Acanthurus coeruleus, in each of three social modes (schooling, territorial, and wandering) in relation to size class, ecological variables, population density and time of day to discern potential determinants of social organization. We found individuals from all three social modes in all four fringing reef habitats (back reef, flat, crest and spur and groove zones) at our main site. Territorial tang density was highest in the flat zone, lowest in the spur and groove zone and negatively related to adult damselfish density. A higher proportion of tangs formed schools in reef zones with the highest densities of territorial damselfishes (spur and groove, crest). In the back reef and flat zones, where damselfish densities were very low, tangs rarely formed schools. Tangs in the wandering mode were most abundant in the back reef. The density of territorial tangs did not change with time of day, but non-territorial tangs tended to wander more in the morning and to form schools more at midday. Small yellow-phase juveniles were always territorial, and the incidence of territoriality decreased in the larger size classes, while schooling and wandering increased. Among similar fringing reefs, the incidence of territoriality increased with increasing population density. These data suggest that life history stage, damselfish density, and conspecific population density are important determinants of blue tang social organization.

Wild animals increase vigilance at the expense of feeding time in response to predation risk or threats from conspecifics. Increased vigilance may therefore indicate increased fear. We tested dairy cattle to determine whether time spent vigilant changed in response to the novelty of their location, the presence of a dog or the presence of an aversive, gentle or unfamiliar handler. We conducted 12 3 min trials per cow on 40 cows tested individually in a large outdoor enclosure containing an attractive food source. The feeders restricted the animal’s view so that it could not feed and scan simultaneously, so vigilance time was defined as any time the animal’s head was raised. During the initial trials, the degree of vigilance was high, but the amount of vigilance decreased significantly with number of trials. Time vigilant was significantly higher in the presence of a dog than in the presence of a human or when neither was present. In a second experiment, 20 cows, that had been trained to recognise an aversive and a gentle person for 3 weeks prior to testing, were tested in an indoor pen containing an attractive food source with the aversive, gentle, or an unfamiliar person nearby. The presence of the aversive person significantly increased vigilance time compared to the unfamiliar and gentle people. However, vigilance time did not decrease with repeated exposure to the enclosure, perhaps because the testing barn was already familiar. These results suggest that cows alter their vigilance according to their degree of fearfulness toward people and toward different environments, and that measures of vigilance may provide information on the degree of fearfulness of the animals. © 2004 Elsevier B.V. All rights reserved.

Although many studies of vigilance examine head raising in foraging, grooming or resting animals, pauses during intermittent locomotion are rarely considered from the perspective of vigilance, and no studies have compared head raising and pausing in the same system. We videotaped central place foraging chipmunks, Tamias striatus, as they approached a patch, collected sunflower seeds, and left to return to their burrows. There was a strong similarity between head raising during foraging and pausing during intermittent locomotion. Chipmunks paused more frequently when moving towards the patch than when leaving the patch. Chipmunks in the patch raised their heads at an intermediate rate, which tended to decrease with time in the patch. Pauses and the duration of motionless periods during head raises were very short (∼0.4 s), and their frequency distributions were similar. Animals remained motionless during 22% of the time spent approaching the patch, 14% of the time spent in the patch and 7% of the time spent leaving the patch. Rates of pausing and head raising generally decreased with short-term familiarity (number of trips to the patch) and with long-term familiarity (proximity of the patch to the burrow). Trials with higher pause rates when approaching the patch had higher head-raising rates in the patch. Whether the focal individual was solitary, dominant or subordinate in a dyad, or competing with multiple chipmunks in the patch had no effect on pausing or head raising. In a separate experiment, exposure to a model hawk increased pause and head-raising rates. We conclude that head raising during foraging and pausing during locomotion serve a similar vigilance function, that this vigilance is directed towards detection of predators rather than conspecifics, and that time allocated to vigilance is sufficient to significantly reduce foraging rates and affect many space use and foraging decisions.

Hibernation is widely regarded as an adaptation to seasonal energy shortage, but the actual influence of energy availability on hibernation patterns is rarely considered. Here we review literature on the costs and benefits of torpor expression to examine the influence that energy may have on hibernation patterns. We first establish that the dichotomy between food- and fat-storing hibernators coincides with differences in diet rather than body size and show that small or large species pursuing either strategy have considerable potential scope in the amount of torpor needed to survive winter. Torpor expression provides substantial energy savings, which increase the chance of surviving a period of food shortage and emerging with residual energy for early spring reproduction. However, all hibernating mammals periodically arouse to normal body temperatures during hibernation. The function of these arousals has long been speculated to involve recovery from physiological costs accumulated during metabolic depression, and recent physiological studies indicate these costs may include oxidative stress, reduced immunocompetence, and perhaps neuronal tissue damage. Using an optimality approach, we suggest that trade-offs between the benefits of energy conservation and the physiological costs of metabolic depression can explain both why hibernators periodically arouse from torpor and why they should use available energy to minimize the depth and duration of their torpor bouts. On the basis of these trade-offs, we derive a series of testable predictions concerning the relationship between energy availability and torpor expression. We conclude by reviewing the empirical support for these predictions and suggesting new avenues for research on the role of energy availability in mammalian hibernation.

The timing and basis of the transition from energy reserve accumulation to reserve utilization in autumn may be a key determinant of winter survival in endotherms, but has rarely been examined directly in the field. In the present study we quantify the energetics of autumn mast hoarding in eastern chipmunks (Tamias striatus) to document the degree to which larder hoarding permits capitalizing on brief pulses of resource abundance and to evaluate the basis of the decision to stop hoarding and initiate hibernation. Daily energy expenditure, measured with the doubly labeled water technique, increased significantly with date and decreasing ambient temperature, eventually exceeding 3× resting metabolic rate in late autumn. Simultaneous documentation of food delivery to burrow larder hoards revealed that delivery rates were low in early autumn, extremely high for a brief period in mid-autumn, then low again in late autumn. Combining estimates of energy expenditure, consumption, and delivery yielded net energy surpluses of 1,320-4,600 kJ day(-1) during the peak hoarding period, meaning total hibernation energy requirements could be acquired in 1-2 days. These results, together with measures of food availability and ambient temperature, suggest that chipmunk activity in late autumn may be affected by both the extent of hoard accumulation and thermoregulatory constraints on sustained energy expenditure. We speculate that both state-dependency and energetic ceilings on autumn hoarding behavior may enhance the capacity of the mast seeding strategy of trees to effectively swamp the foraging efforts of larder-hoarding granivores.

To determine the relationship between within-litter birth weight variation and pre-weaning survival and weight gain, and to provide practical guidance on fostering low-birth-weight piglets, we analyzed piglet survival and weight gain in litters of piglets from 52 sows followed through eight consecutive parities. Litters with high variation in birth weight had more deaths, especially if the litter’s mean birth weight was low. High variation in birth weight was also associated with high variation in weaning weight, but was not significantly related to mean weaning weight. Piglets with birth weights well below the range of most of the litter (‘low-birth-weight piglets’) were more likely to die than their litter-mates, but their weight gains were normal for their birth weight if they survived. These piglets experienced particularly low survival in larger litters and litters from sows of sixth parity or older. Litters containing low-birth-weight piglets started, on average, with more piglets born alive and had a lower pre-weaning survival (with the majority of deaths being low-birth-weight piglets), but did not wean significantly more piglets than litters without low-birth-weight piglets. The majority of litters had a negatively skewed distribution of birth weights, with more piglets well below the mean than well above it. Our data are consistent with the hypothesis that high variation in birth weight contributes to reduced survival, at least for litters of low mean birth weight, and to variable weaning weights. Our data also support the hypothesis that in terms of survival, small piglets have a competitive disadvantage compared to their heavier litter-mates, a disadvantage that is exacerbated in large litters and litters from older sows. Our data suggest that selection for increased litter size that results in more low-birth-weight piglets per litter may not be beneficial unless measures are undertaken to improve the survival of low-birth-weight piglets.

Most physiological and ecological approaches to animal locomotion are based on steady state assumptions, yet movements of many animals are interspersed with pauses lasting from milliseconds to minutes. Thus, pauses, along with changes in the duration and speed of moves, form part of a dynamic system of intermittent locomotion by which animals adjust their locomotor behavior to changing circumstances. Intermittent locomotion occurs in a wide array of organisms from protozoans to mammals. It is found in aerial, aquatic and terrestrial locomotion and in many behavioral contexts including search and pursuit of prey, mate search, escape from predators, habitat assessment and general travel. In our survey, animals exhibiting intermittent locomotion paused on average nearly 50% of their locomotion time (range 6–94%). Although intermittent locomotion is usually expected to increase energetic costs as a result of additional expenditure for acceleration and deceleration, a variety of energetic benefits can arise when forward movement continues during pauses. Endurance also can be improved by partial recovery from fatigue during pauses. Perceptual benefits can arise because pauses increase the capacity of the sensory systems to detect relevant stimuli. Several processes, including velocity blur, relative motion detection, foveation, attention and interference between sensory systems are probably involved. In animals that do not pause, alternative mechanisms for stabilizing the perceptual field are often present. Because movement is an important cue for stimulus detection, pauses can also reduce unwanted detection by an organism's predators or prey. Several models have attempted to integrate energetic and perceptual processes, but many challenges remain. Future advances will require improved quantification of the effects of speed on perception.

Many species of hibernating mammals rely on hoarded food rather than body fat to support winter energy requirements. Here, we evaluate whether the associated ingestive and digestive requirements reduce the benefits that food-storing hibernators can accrue from torpor. Using a simple model, we predict (1) that digestive efficiency could either increase or decrease with increased use of torpor, depending on the Q(10) of digestion relative to the Q(10) of whole-animal metabolism and (2) that increased torpor will result in a linear decrease in energy consumption but an exponential increase in euthermic intake requirements. In 16 captive eastern chipmunks (Tamias striatus), the proportion of time that different individuals spent in torpor was highly variable (29.8%+/-5.9%; 0.0%-86.3%), positively correlated with dry matter digestibility (r2=0.53, P=0.02) and negatively correlated with energy consumption (r2=0.72, P=0.002). Thus, by both increasing conversion efficiency and reducing energy requirements, torpor appears to provide a double benefit for energy conservation by food-storing hibernators. Despite this, a comparative analysis shows that the euthermic intervals of food-storing rodents are four times as long and torpor intervals are half as long as that of fat-storing rodents. Given that required euthermic intake rates are expected to increase exponentially at high levels of torpor, the reduced torpor expression of food-storing species may result from constraints on their ability to load enough food into the gut when euthermic to cover the energy requirements of the subsequent torpor cycle.

We studied territoriality and habitat use by yellow phase juvenile blue tangs, Acanthurus coeruleus, on a small fringing reef in Barbados, West Indies. Juvenile blue tangs occurred on the reef crest, spurs, and a transition zone between the reef crest and reef flat at a density of about 8 individuals per 100 m2, but were much rarer on the reef flat. They were solitary and occupied stable home ranges (median=0.85 m2) that increased with body size. Observational and experimental data documented aggressive defense of home ranges against conspecific and to a lesser extent congeneric, A. bahianus, juveniles (about 7.5 approaches and attacks per hour directed at intruders). Home range locations were structurally more complex and closer to a vertical face than expected by chance. Although juvenile blue tang territories overlapped considerably with those of larger and more aggressive Stegastes damselfish, which are believed to exclude solitary adult Acanthurus spp. from reef crest and spurs, the tangs avoided Stegastes and were rarely chased (

We used a sow-controlled housing system to examine temporal and individual variation in the tendency of sows to associate with young. During a 5-week lactation, 22 sows and litters were housed in a pen where the sow could freely leave and re-enter the piglets’ area by stepping over a barrier that the piglets could not cross. Despite this option, the sows remained with the piglets almost constantly during the 1st day after birth. Nineteen sows (‘leavers’) changed to spending most of their time away from the litter at some point in the lactation. The change was rapid, often within a single week, and occurred in week 2, 3, 4 or 5, depending on the individual. The time of rapid increase in time away was not related to characteristics of the sow or litter, including parity, litter size and sex ratio. Three sows (‘stayers’) did not increase their time away as lactation advanced, and rarely spent more than 15% of their day in the piglet-free area. Nearly all sows showed a clear preference to defecate in the piglet-free area. This study shows 1. that sows voluntarily reduce their contact with the young; 2. that the timing of this reduction varies greatly amongst sows for reasons that may relate to differences in maternal motivation, and 3. that sows do not abandon the litter if the young cannot follow. The clear preference that most sows developed for the piglet-free area reinforces physiological evidence that constant confinement with older litters is aversive for many sows.

Movement of coral reef fishes across marine reserve boundaries subsequent to their initial settlement from the plankton will affect the ability of no-take reserves to conserve stocks and to benefit adjacent fisheries. However, the mobility of most exploited reef species is poorly known. We tagged 1443 individuals of 35 reef fish species captured in Antillean fish traps in the Barbados Marine Reserve and adjacent non-reserve over a two-month period. Trapping and visual surveys were used to monitor the movements of these fish during the trapping period and the subsequent two months. Estimates of distances moved were corrected for the spatial distribution of sampling effort and for the number of recaptures of individual fish. Recapture rates for individual species ranged from 0–100% (median=38%). Species mobility estimated by recapture and resighting were highly correlated. Most species were strongly site attached, with the majority of recaptures and resightings occurring at the site of tagging. However, only one of 59 tagged jacks (Caranx latus, C. ruber) was ever resighted, suggesting emigration from the study area. All species were occasionally recorded away from the sites where they had been tagged (20–500 m), and several species, including surgeonfish, Acanthurus bahianus, A. coeruleus, filefish, Cantherhines pullus, butterflyfish, Chaetodon striatus, angelfish Holocanthus tricolor and parrotfish, Sparisoma viride, ranged widely within reefs. In contrast, few movements were observed between reefs separated by more than 20 m of sand and rubble, and no emigration from the Reserve was recorded. Most reef fishes vulnerable to Antillean traps appear sufficiently site-attached to benefit from reserves. However, many species move over a wide enough area to take them out of small reserves on continuous reef. Use of natural home range boundaries could minimize exposure of fishes in reserves to mortality from adjacent fisheries.

Reserves are being used increasingly to conserve fish communities and populations under threat from overfishing, but little consideration has been given to how fish behavior might affect reserve function. This review examines the implications of how fish use space, in particular the occurrence and size of home ranges and the frequency and direction of home range relocations. Examples are drawn primarily from the literature on coral reef fishes, but the principles apply to other habitats. Reserves can protect fish species only if individuals restrict their movements to a localized home range during at least part of the life cycle. Home range sizes increase with body size. In small reserves, a significant proportion of fish whose home ranges are centered within the reserve can be exposed to fishing mortality because their home ranges include non-reserve areas. Relocation of home ranges following initial settlement increases exposure to the fishery, especially if habitat selection is frequency-dependent. Distance, barriers, and costs of movement counter such redistribution. These considerations lead to predictions that population density and mean fish size (1) will form gradients across reserve boundaries with maxima in the center of the reserve and minima outside the reserve away from the boundary; (2) will increase rapidly in newly established reserves, only later providing ‘spillover’ to adjacent fisheries as density-dependent emigration begins to take effect; and (3) will be higher in reserves that are larger and have higher area:edge ratios, more habitat types, natural barriers between reserve and non-reserve areas, and higher habitat quality inside than outside the reserve. (4) Species with low mobility and weak density-dependence of space use will show the greatest increase in reserves and the strongest benefit for population reproductive capacity, but those with intermediate levels of these traits will provide the greatest spillover benefit to nearby fisheries.

Surgeonfish (Acanthuridae) are prominent, herbivorous members of coral reef communities that occur as dispersed individuals and small, loose groups ('non-schooling fish') or as members of large, highly aggregated, mixed-species schools ('schooling fish'). We examined the relationships among fish size, habitat use and schooling in two species of surgeonfish on a fringing reef in Barbados, West Indies. Both ocean surgeonfish, Acanthurus bahianus, and blue tangs, A. coeruleus, appeared to show ontogenetic habitat shifts. The density of juvenile ocean surgeonfish was highest in the back reef (inshore), lower on the reef crest (intermediate) and lowest in the spurs and grooves (offshore) zone, but schooling adults were most abundant in the spurs and grooves zone. In a multiple regression considering the effects of depth, algal cover, rugosity and distance from shore, the density of non-schooling ocean surgeonfish was positively associated with percent algal cover on the substratum and negatively with distance from shore. Newly settled blue tangs occurred only in the reef crest and spurs and grooves zones, but larger juveniles were more common in the back reef, while adults were more evenly distributed across zones. The density of non-schooling blue tang was positively associated with rugosity, distance from shore, and percent algal cover. In both species, schooling occurred primarily in adults; small juveniles never participated in the large, dense schools. The proportion of adults that were schooling increased from the back reef to the reef crest to the spurs and grooves zone. These results are consistent with the hypothesis that schooling permits adult surgeonfish access to higher quality food in the territories of damselfish (Pomacentridae) that predominate on the reef crest and spurs.

Juvenile pollock (Pollachius virens) school in open water at low tide and disperse in beds of intertidal algae at high tide. The goal of the present study was to determine whether both aggregation and use of algal habitat represent alternative antipred- ator tactics for pollock, and whether their occurrence depended on the number of fish present and the amount of algal habitat available. We systematically varied fish density and algal availability in large (8-M2) arenas and examined distributions before and after exposure to an avian predator model, a stuffed cormorant (Phalacrocorax auritus). Pollock preferred the algal habitat, and the proportion of fish in the algae increased as the amount of algal habitat increased. When density of fish in the arena increased, the number of fish in the algal habitat increased, but the proportion decreased. Following exposure to the predator model, the proportion of fish in the algae increased. Fish in the open were aggregated most of the time, but there was a trend toward increased aggregation of those fish remaining in the open following exposure to the predator. Thus, the use of two alternative antipredator tactics can produce very dynamic spatial distributions. Because the benefits of aggregations are positively density dependent while those of refuges are likely negatively density de- pendent, species that use both tactics are likely to show dramatic shifts in habitat distribution with changes in population size and refuge availability.

We examined how spatial distribution and the use of aggressive behavior by blue gouramis, Trichogaster trichopterus (Belontiidae), in the presence of a concentrated food source were affected by group size and by the short-term presence and absence of food. Gouramis aggregated in the area of the food source, and the frequency of aggressive acts per fish was higher for fish near the food source than for fish away from it. The frequency of aggressive acts per fish near the food source decreased with group size and was about 50 times higher in groups of 2 and 4 than it was in groups of 16 and 32. In group sizes 2 and 4, the frequency of aggression was unaffected by the presence and absence of food, but in larger group sizes aggression increased during short intervals without food. The mean proportion of time spent near the food source increased from group size 2 to group size 8 and decreased from group size 8 to group size 32 and was greater during intervals of food availability than during intervals in which food was not available. We suggest that gouramis adjust their relative use of contest and scramble competition according to the costs and benefits of aggression as determined by the number of competitors and by the potential for missed feeding opportunities. The average proportion of time spent in the vicinity of the food source appears to be influenced by both the rate of aggression and by the net rate of gain available.

Daniel E. Ruzzante,* David C. Hamilton, Donald L. Kramer, and James W. A. Grant* "Department of Biology, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada, Department of Mathematics, Statistics, and Computing Science, Dalhousie University, Halifax, Nova Scotia B3H 3J5, Canada, Department of Biology, McGill University, 1205 Docteur Penfield Avenue, Montreal, Quebec H3A 1B1, Canada, and Department of Biology, Concordia University, 1455 Boulevard de Maisonneuve West, Montreal, Quebec H3G 1M8, Canada

We examined the relationship between the intestine length and the amount of plant material in the diet of 21 species of fish from forest streams in Panama. Alimentary tract analyses supplemented by literature reports showed that four loricariid catfish species and one poeciliid were specialized herbivores consuming almost exclusively periphyton and detritus. Four species, including one erythrinid, one characid, one trichomyctycterid and one eleotrid, were carnivores consuming almost entirely food of animal origin. Twelve species, including five characids, one lebiasinid, two pimelodelids, three cichlids and one poeciliid, were omnivores consuming food of both plant and animal origin, but the average proportion of food of plant origin (detritus and algae plus higher plant parts) varied from 4–60%. Most omnivores increased plant food consumption with increasing size. Because intestine length increases allometrically with body size and the pattern of increase differs considerably among species and is influenced by length:mass relationships, we compared species at the same size and took both length and mass into account. At a given size, intestine lengths of herbivores were longer than those of omnivores, and these were longer than those of carnivores. Differences in intestine length among the dietary categories were greater at larger body sizes and when the common size was defined by body mass than when it was defined by body length. There was no trend for the average proportion of plant material consumed to be related to intestine length among the omnivores, when confounding effects of body mass were taken into account. The slopes of the allometric equations relating log10 intestine length to log10 body size for herbivores tended to be higher than for omnivores and higher for omnivores than for carnivores, but both herbivores and omnivores showed extensive variation and overlap with the other dietary categories. Among the omnivores, there was no trend for slopes to be steeper for species consuming more plant material on average or for species showing larger ontogenetic increases in plant consumption. These results permit increased precision in describing diet-intestine length relationships, but indicate that the widely held belief that intestine length reflects diet in fishes should only be applied to broad dietary categories and not to finer divisions among omnivores.

We examined the ontogenetic allometry of intestine length in relation to body length and body mass in 21 species of fish from forest streams in Panama. The relationships between log10 intestine length and log10 body length and mass were well described by linear regressions, although some species showed slight curvilinearity. Slopes and intercepts of the linear regressions varied considerably among species. Intestine length was positively allometric in most species, with slopes of the intestine length:body length relationship ranging from 1.09 to 2.11. Relative intestine lengths (intestine length/body length) varied by two orders of magnitude (0.39–38.44) in the data set as a whole, but the variation was about one order of magnitude when species were compared at a common body size. Species in which body mass increased more rapidly with body length had more rapid increases in intestine length with body length. Among omnivorous and carnivorous species compared at the same body length, heavier species had longer intestines. Interspecific comparisons of relative intestine length may produce misleading conclusions unless comparisons are made at a common size and account for differences in relative mass.

When central place foragers compete aggressively for patchy resources, subordinates may be preventedfrom collecting food until a dominant has departed with its load. Extensions of central place foraging models predict that animals forced to wait at a patch should increase their load sizes and patch times aswell as their tendency to search for and switch to alternative patches. We tested these predictions usingeastern chipmunks, Tamias striatus, hoarding sunflower seeds collected from seed/vermiculite mixturesin trays placed 5-8 m from their burrows. By using her hand to prevent access to the patch, the experimentersubjected animals to progressively increasing waiting times at two seed densities; another series of trialsat the same seed densities monitored a similar number of trips without imposed waiting. As predicted, patch times and load sizes were higher in sessions with imposed waiting than in control sessions. Loadsizes increased with trial number in experimental sessions but decreased or remained the same in controlsessions. Chipmunks spent more of their time searching for alternative patches during trials with imposed waiting than during controls. They also started searching for alternative patches at lower levels of imposed waiting when using poor than when using rich patches. These results indicate that the effects of interference on foraging decisions and on spatial overlap between individuals can be predicted by simple economic models. Furthermore, the results suggest how resource-defense tactics can be predicted by the economic effects of interference on the foraging efficiency of the opponent.

Functional connectivity, the degree to which the landscape facilitates or impedes movement, depends on how animals perceive costs and benefits associated with habitat features and integrate them into a movement path. There have been few studies on functional connectivity in marine organisms, despite its importance for the effectiveness of Marine Protected Areas. In this study, we asked how open sand and conspecific distribution affected functional connectivity of longfin damselfish (Stegastes diencaeus) on fringing reefs in Barbados. We translocated 102 individuals to sites varying in sand gap width and in configuration: Continuous (solid reef between release site and territory); Detour (sand along the direct path between release site and territory, but an alternative, continuous solid U-shaped reef path); and Patch (sand between release site and territory, but an alternative stepping stone path). We visually tracked and mapped every homing path. We found no evidence of a barrier to movement in the Continuous configuration, but sand was a partial barrier in Detour and Patch configurations. The probability of crossing the sand gap dropped below 50% when its width was >1.85 m in Detour and >3.90 m in Patch configuration. Damselfish avoiding large gaps took detours that approximated the route maximizing travel over reef, but they crossed more short sand gaps and fewer conspecific territories, suggesting avoidance of agonistic interactions. This study quantifies for the first time the size and steepness of a barrier to movement in a marine organism, and it provides evidence for effects of both landscape configuration and conspecific distribution on functional connectivity.

Abstrac-t.We have developed a model that reconciles information-sharing and producerscrounger models of group foraging. Our model includes producers, scroungers, and an opportunistic forager that can both produce and scrounge but with reduced efficiency. We show that these three strategies can coexist only in the unlikely case that the opportunist's loss in searching ability is exactly equal to its gain in scrounging ability. However, all pairs of strategies can coexist. Three parameters control the proportions of coexisting strategists: the degree of compatibility between the opportunist's producing and scrounging activities; the proportion of food patches that are shared with scrounging individuals; and the effective group size. When there is little incompatibility between producing and scrounging, opportunists will always be present, unless the producer is able to consume most of the patch without sharing. The opportunist strategy is always excluded when there is a high degree of incompatibility between producing and scrounging. We consider the organismal and ecological factors that are likely to affect all three parameters. Our model predicts that scrounging behavior is likely to be selected in a wide range of foraging groups and that it may impose a considerable cost on sociality.

To investigate the effect of familiarity'with the local terrain on the ability to escape predators, we recorded the type of refuge chosen and the distance and time required to reach it, for chipmunks escaping a pursuing human at different distances from their burrows. Chipmunks never used their burrow as a refuge unless the chase was initiated within 2.5 m of the burrow entrance. The final refuge was commonly farther than the burrow entrance. Chipmunks were most likely to take refuge in holes other than their burrow when chased within their home range, whereas they were most likely to flee up trees when chased outside their home range. Chipmunks released within their home range (10 m from burrow) took only half as much time and travelled only half as far to reach a refuge as they did when released outside their normal home range (100 m from burrow)

SUMMARY (1) This study examines the population ecology of Poecilia gillii (Kner & Steindachner, 1863), a small algae- and detritus-feeding fish, inhabiting sixteen isolated, residual pools of a high-gradient, intermittent stream in Costa Rica following floods which severely reduced the number of fish in the stream. (2) Immediately after the floods, population sizes averaged 20% and pool surface areas 130% of their pre-flood values, periphyton production was relatively low and dissolved oxygen was relatively high. Among pools, population densities were not correlated with their pre-flood values, and the population growth rates showed a weak negative correlation with density, a marginal positive correlation with periphyton production and no correlation with oxygen. (3) Near the end of the 153-day post-flood study period, population sizes had risen to 50% of their pre-flood values, while pool areas had fallen to 73% of their preflood values. Periphyton production was relatively high and dissolved oxygen was very low. Among pools, population densities were correlated with their pre-flood values, and the population growth rate showed a strong negative correlation with population density and strong positive correlations with periphyton production and dissolved oxygen level. (4) These results suggest that in highly seasonal tropical environments, temporal patterns of population abundance in high-gradient streams will be very different from those in floodplains, where the rainy season is a time of increase and the dry season a time of decline. Spatial variation in environmental characteristics which control periphyton, detritus and oxygen availability may produce characteristic population densities in different pools. An increase in the proportion of males and a decrease in their size after the floods suggest social inhibition of sexual maturation during the late dry season.

The behavior of dwarf gouramis (Colisa lalia, Pisces, Belontiidae) and their vulnerability to predation by snakeheads (Channa micropeltes, Pisces, Channidae) were observed at four dissolved oxygen concentrations. When the oxygen level was near saturation (8 ppm) or only moderately reduced (3 ppm), the gouramis rarely breathed air and spent most of their time in a patch of artificial vegetation. At extremely low oxygen concentrations (1 and 0 ppm) the gouramis increased their air-breathing frequency and spent less time in cover. Gouramis were more likely to be captured by the snakeheads when out of the vegetation, and thus were caught more quickly at lower oxygen levels, even though their air-breathing frequency declined and use of cover increased in the presence of the predators. These results indicate that dissolved oxygen concentration, which varies considerably in many fish habitats, can affect use of cover and risk of predation in fishes.

The bimodally respiring catfish Clarias macrocephalus Gunther responded to a toxic extract of Croton tiglium (Euphorbiaceae) seeds by increased air breathing under both normoxic (8.1 ± 0.4 mgO2 l−1) and hypoxic (0.7 ± 0.1 mgO2l−1) conditions. Fish in hypoxia survived longer than those in normoxia when surface access was provided. When air breathing was prevented, survival time in toxin was greatly reduced at both levels of dissolved oxygen, and fish in normoxia survived longer than those in hypoxia. Non-toxin controls without surface access survived in normoxia but in hypoxia died at the same time as the fish in toxin. These results suggest that air breathing increases the resistance offish to toxins by permitting a decrease in the rate of gill ventilation and hence the rate at which toxins are absorbed.

The reproductive seasons of 6 species of characoid fishes inhabiting a tropical forest stream in Panama were determined from observations on gonadal condition and size frequency distribution of the populations over an 18—mo period. In this area the relatively mild dry season lasts °4 mo, stream discharge increases moderately during the rainy season, floods are intense but brief and temperature is very stable. Bryconamericus emperador and Piabucina panamensis spawned in temporary tributaries in June with the first floods of the rainy season. Brycon petrosus and Hyphessobrycon panamensis spawned in the dry season. The majority and adult Gephyrocharax atricaudata were mature in most months, but fry appeared in several peaks scattered through both dry and rainy seasons. Roeboides guatemalensis seemed to breed throughout the year but with a dry season peak. Previous studies of tropical freshwater fishes have emphasized the widespread tendency toward a flood spawning pattern but have investigated primarily highly seasonal savanna environments. I suggest that the diversity in the present study is related to the relatively stable habitat. Five hypotheses to explain the diversity in the timing of reproduction are proposed and briefly discussed: reproductive seasonality (1) is controlled by adult or juvenile food availability, (2) is controlled by interspecific competition for food among juveniles, (3) is controlled by competition for spawning sites, (4) is a mechanism for reproductive isolation, or (5) is unrelated to local conditions but is a reflection of earlier evolution of specializations for spawning under particular conditions.

This study was undertaken to determine the effect of vasectomy and tubal section on spontaneous locomotive movement and exploratory behavior in mice which might reflect an alteration in endocrine function. Adult Swiss Webster mice were either vasectomized tubectomized castrated or sham-operated upon. Controls were not operated on. 45 days after operation spontaneous movement in a box was recorded by an electronic field and exploratory behavior was d:termined from activities in another box with marked lines which recorded searching activities. Spontaneous movement was 1.7 greater in normal or sham-operated mice than in vasectomized (p less than .001) and 1.3 times greater than in castrate animals (p less than .05). Tubectomy and ovariectomy had the same effects as vasectomy or castration but with more variability. Exploratory behavior was slightly less in tubectomized mice. It was concluded that vasectomized or tubectomized mice had 60% less spontaneous movement than normal mice 45 days after operation; exploratory behavior was not significantly influenced by either operation. Results do not confirm findings reported by others than vasectomy enhances testosterone secretion or rejuvinates the organism. A degenerative effect is suggested.