Modeling Behavior by Coastal River Otter (Lontra Canadensis) in Response to Prey Availability in Prince William Sound,Alaska: A Spatially-Explicit Individual-Based Approach

Effects of climate change on animal behavior and cascading ecosystem responses are rarely evaluated. In coastal Alaska, social river otters (Lontra Canadensis), largely males, cooperatively forage on schooling fish and use latrine sites to communicate group associations and dominance. Conversely, solitary otters, mainly females, feed on intertidal-demersal fish and display mutual avoidance via scent marking. This behavioral variability creates “hotspots” of nutrient deposition and affects plant productivity and diversity on the terrestrial landscape. Because the abundance of schooling pelagic fish is predicted to decline with climate change, we developed a spatially-explicit individual-based model (IBM) of otter behavior and tested six scenarios based on potential shifts to distribution patterns of schooling fish. Emergent patterns from the IBM closely mimicked observed otter behavior and landscape use in the absence of explicit rules of intraspecific attraction or repulsion. Model results were most sensitive to rules regarding spatial memory and activity state following an encounter with a fish school. With declining availability of schooling fish, the number of social groups and the time simulated otters spent in the company of conspecifics declined. Concurrently, model results suggested an elevation of defecation rate, a 25% increase in nitrogen transport to the terrestrial landscape, and significant changes to the spatial distribution of “hotspots” with declines in schooling fish availability. However, reductions in availability of schooling fish could lead to declines in otter density over time.     

Modelling changes in migration pattern of herring: collective behaviour and numerical domination

According to the adopted-migrant hypothesis, first time spawning herring Clupea harengus learn their migration pattern from schooling with older individuals. Changes in migration pattern of Norwegian spring-spawning herring co-occur with the recruitment of abundant year classes to the spawning stock. It is argued that this is due to the abundant year classes being unable to learn from the older ones since most of the recruiting year class only experience their own naïve class-mates. An individual-based school simulation study is presented to explore the hypothesis. Behaviour is simulated using individual rules that take into account the movements of nearby individuals. After establishing a schooling pattern, a small proportion of the individuals is directed to move towards a given position while the remaining individuals keep using their behaviour rules. When <4% of the individuals are so directed there is no response seen in the remaining school. But when ≥7% of the total school is directed to a specific location, the remaining individuals always respond and follow the directed individuals. The simulations thus show that determined individuals can have a substantial influence on the collective behaviour of schools. Furthermore, the knife-edge response in school behaviour suggests that the relative abundance of determined individuals in a school plays an important part in the collective behaviour. This mechanism can explain the observed changes in migration pattern of Norwegian spring-spawning herring associated with the recruitment of abundant year classes to the adult Stock.     

Back to school: can antipredator behaviour in guppies be enhanced through social learning?

The ability to recognize and respond to predators often has a learned component, but few studies have examined the role of social learning in the development of antipredator behaviour. We investigated whether wild-caught juvenile guppies, Poecilia reticulata, from a low-predation river in Trinidad increase their response towards a novel predator through association with conspecifics from a high-predation river. We assigned fish to one of three treatment groups: (1) repeated exposure to a model accompanied by high-predation conspecifics; (2) repeated exposure to a model with low-predation conspecifics; (3) a control group in which focal fish interacted with high-predation fish in the absence of the model. Guppies trained with high-predation, but not low-predation, ‘demonstrators’ significantly improved their antipredator behaviour (spent more time schooling and inspected the model from further away). The guppies assigned to the control group showed no significant improvement in antipredator behaviour after the training period, suggesting that association with experienced conspecifics in the absence of the model is not sufficient to enhance the antipredator behaviour of na?ve fish. We conclude that guppies can improve their antipredator behaviour through association with more experienced conspecifics in the presence of visual cues simulating high predation risk. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.        

Effects of Emergence Time and Early Social Rearing Environment on Behaviour of Atlantic Salmon: Consequences for Juvenile Fitness and Smolt Migration

Consistent individual differences in behaviour have been well documented in a variety of animal taxa, but surprisingly little is known about the fitness and life-history consequences of such individual variation. In wild salmonids, the timing of fry emergence from gravel spawning nests has been suggested to be coupled with individual behavioural traits. Here, we further investigate the link between timing of spawning nest emergence and behaviour of Atlantic salmon (Salmo salar), test effects of social rearing environment on behavioural traits in fish with different emergence times, and assess whether behavioural traits measured in the laboratory predict growth, survival, and migration status in the wild. Atlantic salmon fry were sorted with respect to emergence time from artificial spawning nest into three groups: early, intermediate, and late. These emergence groups were hatchery-reared separately or in co-culture for four months to test effects of social rearing environment on behavioural traits. Twenty fish from each of the six treatment groups were then subjected to three individual-based behavioural tests: basal locomotor activity, boldness, and escape response. Following behavioural characterization, the fish were released into a near-natural experimental stream. Results showed differences in escape behaviour between emergence groups in a net restraining test, but the social rearing environment did not affect individual behavioural expression. Emergence time and social environment had no significant effects on survival, growth, and migration status in the stream, although migration propensity was 1.4 to 1.9 times higher for early emerging individuals that were reared separately. In addition, despite individuals showing considerable variation in behaviour across treatment groups, this was not translated into differences in growth, survival, and migration status. Hence, our study adds to the view that fitness (i.e., growth and survival) and life-history predictions from laboratory measures of behaviour should be made with caution and ideally tested in nature.     

Response of seaward-migrating European eel (Anguilla anguilla) to manipulated flow fields

Anthropogenic structures (e.g. weirs and dams) fragment river networks and restrict the movement of migratory fish. Poor understanding of behavioural response to hydrodynamic cues at structures currently limits the development of effective barrier mitigation measures. This study aimed to assess the effect of flow constriction and associated flow patterns on eel behaviour during downstream migration. In a field experiment, we tracked the movements of 40 tagged adult European eels (Anguilla anguilla) through the forebay of a redundant hydropower intake under two manipulated hydrodynamic treatments. Interrogation of fish trajectories in relation to measured and modelled water velocities provided new insights into behaviour, fundamental for developing passage technologies for this endangered species. Eels rarely followed direct routes through the site. Initially, fish aligned with streamlines near the channel banks and approached the intake semi-passively. A switch to more energetically costly avoidance behaviours occurred on encountering constricted flow, prior to physical contact with structures. Under high water velocity gradients, fish then tended to escape rapidly back upstream, whereas exploratory ‘search’ behaviour was common when acceleration was low. This study highlights the importance of hydrodynamics in informing eel behaviour. This offers potential to develop behavioural guidance, improve fish passage solutions and enhance traditional physical screening.     

Narrow-Front Loop Migration in a Population of the Common Cuckoo Cuculus canorus,as Revealed by Satellite Telemetry

Narrow migration corridors known in diurnal, social migrants such as raptors, storks and geese are thought to be caused by topographical leading line effects in combination with learning detailed routes across generations. Here, we document narrow-front migration in a nocturnal, solitary migrant, the common cuckoo Cuculus canorus, using satellite telemetry. We tracked the migration of adult cuckoos from the breeding grounds in southern Scandinavia (n = 8), to wintering sites in south-western Central Africa (n = 6) and back to the breeding grounds (n = 3). Migration patterns were very complex; in addition to the breeding and wintering sites, six different stopover sites were identified during the 16,000 km annual route that formed a large-scale clockwise loop. Despite this complexity, individuals showed surprisingly similar migration patterns, with very little variation between routes. We compared observed tracks with simulated routes based on vector orientation (with and without effects of barriers on orientation and survival). Observed distances between routes were often significantly smaller than expected if the routes were established on the basis of an innate vector orientation programme. Average distance between individuals in eastern Sahel after having migrated more than 5,000 km for example, was merely 164 km. This implies that more sophisticated inherent guiding mechanisms, possibly involving elements of intermediate goal area navigation or more elaborate external cues, are necessary to explain the complex narrow-front migration pattern observed for the cuckoos in this study.     

Population Differences in the Schooling Behaviour of Newborn Guppies,Poecilia reticulata

Population differences in the schooling behaviour of adult guppies (Poecilia reticulata) from Trinidad have previously been well documented. This paper demonstrates that variation in schooling behaviour is also present in newborn fish. Guppies from the Aripo River of Trinidad display well-developed schooling behaviour from birth. In addition to forming cohesive and polarized groups, these newborn fish also exhibit predator inspection behaviour. Newborn guppies from the Paria River perform inspections but, unlike the Aripo fish, are poor schoolers. Population variation in behaviour at birth does not necessarily reflect the pattern observed in the adult fish. As adults, guppies from the Upper section of the Aripo River have a much lower schooling tendency and are less wary during inspection than the downstream Lower Aripo guppies. At birth, however, the schooling behaviour and inspection behaviour in the two populations is identical. These results suggest that different selective pressures operate on adult and newborn guppies in Trinidad.     

The impact of individual perceptual and cognitive factors on collective states in a data-driven fish school model

In moving animal groups, social interactions play a key role in the ability of individuals to achieve coordinated motion. However, a large number of environmental and cognitive factors are able to modulate the expression of these interactions and the characteristics of the collective movements that result from these interactions. Here, we use a data-driven fish school model to quantitatively investigate the impact of perceptual and cognitive factors on coordination and collective swimming patterns. The model describes the interactions involved in the coordination of burst-and-coast swimming in groups of Hemigrammus rhodostomus. We perform a comprehensive investigation of the respective impacts of two interactions strategies between fish based on the selection of the most or the two most influential neighbors, of the range and intensity of social interactions, of the intensity of individual random behavioral fluctuations, and of the group size, on the ability of groups of fish to coordinate their movements. We find that fish are able to coordinate their movements when they interact with their most or two most influential neighbors, provided that a minimal level of attraction between fish exist to maintain group cohesion. A minimal level of alignment is also required to allow the formation of schooling and milling. However, increasing the strength of social interactions does not necessarily enhance group cohesion and coordination. When attraction and alignment strengths are too high, or when the heading random fluctuations are too large, schooling and milling can no longer be maintained and the school switches to a swarming phase. Increasing the interaction range between fish has a similar impact on collective dynamics as increasing the strengths of attraction and alignment. Finally, we find that coordination and schooling occurs for a wider range of attraction and alignment strength in small group sizes.     

Year-Round Tracking of Small Trans-Saharan Migrants Using Light-Level Geolocators

Since 1899 ringing (or banding) remained the most important source of information about migration routes, stopover sites and wintering grounds for birds that are too small to carry satellite-based tracking systems. Despite the large quantity of migrating birds ringed in their breeding areas in Europe, the number of ring recoveries from sub-Saharan Africa is very low and therefore the whereabouts of most small bird species outside the breeding season remain a mystery. With new miniaturized light-level geolocators it is now possible to look beyond the limits of ring recovery data. Here we show for the first time year round tracks of a near passerine trans-Saharan migrant, the European Hoopoe (Upupa epops epops). Three birds wintered in the Sahel zone of Western Africa where they remained stationary for most of the time. One bird chose a south-easterly route following the Italian peninsula. Birds from the same breeding population used different migration routes and wintering sites, suggesting a low level of migratory connectivity between breeding and wintering areas. Our tracking of a near passerine bird, the European Hoopoe, with light-level geolocators opens a new chapter in the research of Palaearctic-African bird migration as this new tool revolutionizes our ability to discover migration routes, stopover sites and wintering grounds of small birds.     

School fidelity in fishes: The yellow perch pattern

School fidelity concerns the cohesiveness of social aggregations over time, as measured by the regularity or repeatability with which known individuals re-occur as members of a school. School fidelity was measured by divers who observed yellow perch (Perca flavescens) marked with individually recognizable tags in Cazenovia Lake, New York. Yellow perch were facultative schoolers, with individual differences in schooling tendency (measured as percentage of time in schools) accounting for different numbers of observations of schooled versus solitary fish. The greatest co-occurrence was found between fish with strong schooling tendencies, but within this group co-occurrence was random. Home ranges overlapped greatly between individuals, yet co-occurrence was more a function of schooling tendency than of overlapping home ranges. Individuals with overlapping home ranges but with weak schooling tendencies seldom co-occurred. Home range size increased directly with schooling tendency: the distances that individuals moved apparently depended on the movements of the schools they joined, with strongly schooling fish remaining in schools longer. Individuals joined and left schools frequently; this also reflects a lack of fidelity between fish. Fish schools that form primarily for predator avoidance may show higher levels of fidelity than do schools that form for foraging or hydrodynamic efficiency.     

Presettlement schooling behaviour of a priacanthid,the Purplespotted Bigeye Priacanthus tayenus (Priacanthidae: Teleostei)

We report in situ behavioural observations of presettlement schooling in Priacanthus tayenus off Coral Bay, Western Australia collected using pelagic Baited Remote Underwater stereo-Video systems. Two groups of fish (8 and 9 individuals) were observed that aggregated into a single school. Mean total length was 24.1 mm (12.5–30.2 mm). The fish swam at a mean speed of 8.5 cm s^?1 in a group spacing themselves more or less evenly at a distance of around one body length from the nearest neighbour within the school. P. tayenus appeared to be sometimes associated with juveniles of other species. The results presented here add to the limited, but growing body of literature on the schooling behaviour of the early pelagic stages of demersal fishes.     

The ontogeny of twilight migration patterns in grunts (Pisces: Haemulidae)

The development of dusk and dawn migratory behaviours was investigated in French and white grunts (Haemulon flavolineatum and H. plumieri) at St. Croix, U.S. Virgin Islands. Four juvenile stages were recognized: small, medium, transitional, and large. Each stage differed in age, size, coloration, habitat preference, diel foraging patterns, and twilight migratory behaviour. Comparisons between medium (15 to 30 mm long, 30 to 50 days old) and large juveniles (40 to 120 mm, 80 to 700 days) were emphasized. Medium juveniles occurred in small, diurnally feeding groups near sea urchins in the sand halo around a reef. Group composition varied during the day. They migrated at 15 min after sunset, moving hesitantly from halo to grassbed. Migration routes remained constant over a month, but differed over two years. Large juveniles fed nocturnally, formed daytime resting schools over coral heads, and migrated at 25 min after sunset. Compared with medium fish, resting site constancy was greater during a day, migration activities were significantly less variable, and migration routes remained relatively constant for two years.Ontogenetic differences in constancy of daytime school locales and migration routes may result from learning, facilitated perhaps by greater overlap of age cohorts in large juveniles. Other differences in behavioural variability may result from ontogenetic development of the visual apparatus, plus stabilizing selection due to greater predation on smaller, behaviourally variable fish.     

The social organization of adult blue tangs, <Emphasis Type="Italic">Acanthurus coeruleus</Emphasis>, on a fringing reef,Barbados, West Indies

Blue tangs in Barbados exhibit three distinct social modes: territorial, schooling and wandering. We compared the mobility, foraging, aggression performed and received and the use of cleaning stations of adult blue tangs among modes and among habitats within a single fringing reef in Barbados. Evidence from observed switches during focal observations and multiple observations of tagged individuals indicate that fish are either territorial or non-territorial. Non-territorial fish formed schools and wandered. However, wandering can be used during solitary movements by fish in either type. Fish in the territorial mode, not previously described in adults of this species, restricted activity to a small area overlapping the territories of other tangs. They actively chased conspecifics and were chased mostly by damselfishes. They swam more slowly and fed at higher rates than other modes. Fish in the schooling mode ranged widely in compact, polarized groups of conspecifics, congeners and other species. They were not aggressive and were attacked mostly by damselfishes. They swam rapidly and fed at intermediate rates. Fish in the wanderer mode showed neither aggression nor association with other individuals. They swam rapidly, well above the substrate, fed little, were chased by conspecifics, ocean surgeonfish, A. bahianus, and damselfish and visited cleaning stations more often then other modes. All three modes were observed in all four main zones of the reef, and their behaviour changed quantitatively with habitat type. We suggest that territoriality reduces competition for algal food, schooling allows fish to overcome the food defence by damselfish, tangs and ocean surgeonfish, and wandering permits solitary movement over the reef to cleaning stations, feeding sites and other resources.     

Schooling behaviour and retinomotor response of juvenile Pacific bluefin tuna Thunnus orientalis under different light intensities

Schooling behaviour and histological retinal light adaptation in juvenile Pacific bluefin tuna Thunnus orientalis were examined under various light intensities to determine the effect of light intensity on behaviour. After monitoring the schooling behaviour of juveniles 35–36 and 45–46 days post hatching, schooling variables such as nearest neighbour distance and separation swimming index were measured under different light intensities. Furthermore, retinal indices of light adaptation were investigated histologically for each experimental light intensity. Under intensities >5 lx, schooling variables in the two juvenile growth stages were nearly constant, allowing schooling. In contrast, the schooling variables indicated that the fish gradually swam more widely and randomly with decreasing light intensities <5 lx. The retinal indices also showed a shift from light adaptation to dark adaptation at light levels <5 lx. From 5 to 0·01 lx, retinal adaptation and fish schooling behaviour changed with light intensity. These data suggest that the schooling behaviour of juvenile Pacific bluefin tuna is greatly affected by retinal adaptation.     

A standardized method for quantifying consistent individual differences in schooling behaviour

A method for quantifying consistent individual differences in schooling behaviour is presented. This method, which utilizes a school of models, improves on previous methods by removing the unwanted variation that is introduced by live stimulus fish while still providing the physiological experience of schooling to the focal fish. Three‐spined stickleback Gasterosteus aculeatus observed in the model school assay exhibited consistent individual differences in schooling behaviour.     

Response of downstream migrant juvenile Pacific salmonids to accelerating flow and overhead cover

Mechanical structures designed to divert or guide juvenile migrant salmon at dams often work less effectively than expected. This likely results from a lack of understanding of fish behaviour. In order to address this, a series of experiments was conducted at McNary dam, USA, to assess the influence of hydraulic transition and overhead cover on the behaviour of seaward migrating juvenile Pacific salmon. Fish passing through a flume encountered a choice of route that varied based on hydraulic factors and overhead cover. Direct observation revealed that individuals elicited strong avoidance behaviour when they encountered areas where hydraulic conditions changed rapidly or were covered. Our findings have implications relevant to fish pass design and culvert restoration in Europe. Critically, improvement of current fish pass design and development of alternative mechanisms that effectively block fish access to, and divert fish away from poor passage routes, requires consideration of the behavioural component of fish migration. Guest editors: R. L. Welcomme & G. Marmulla Hydropower, Flood Control and Water Abstraction: Implications for Fish and Fisheries     

The influence of habitat stability on landmark use during spatial learning in the three-spined stickleback

The capacity to learn enables animals to match their phenotypic response to a changing environment on the basis of experience but learning is likely to incur costs such as the cost of making mistakes or the energetic cost of processing information. Little is known about how animals optimize the use of learned behaviour within their natural environments such that potential costs are minimized. We investigated whether the use of local landmarks in learning orientation routes by the three-spined stickleback, Gasterosteus aculeatus, varied in response to the visual stability of their natural habitats. Sticklebacks collected from five fast-flowing rivers and five ponds were trained to locate a hidden reward in a T-maze. Locating the reward required the fish to learn a body-centred algorithmic behaviour (turn left or right) or to follow plant landmarks. Probe trials, in which these cues conflicted, revealed which spatial cue the fish was using. Pond fish appeared to rely more than river fish on visual landmarks, which is consistent with the suggestion that even within a species, learned behaviour is fine-tuned in response to local environmental conditions. Landmarks may be reliable indicators of location only in stable pond habitats. In rivers, turbulence and flow may continually disrupt the visual landscape such that river fish may benefit from learning orientation routes only if learning is constrained so that unreliable visual cues are ignored. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

Lateralisation of visual function in yellow-eyed mullet (Aldrichetta forsteri) and its role in schooling behaviour

Lateralisation of cognitive function is a common phenomenon found throughout the animal kingdom. In fish, lateralisation is involved in visually mediated behaviours such as schooling, predator avoidance and foraging. This study sought to quantify visual laterality in yellow-eyed mullet (Aldrichetta forsteri), to determine visual asymmetries and the significance of lateralisation, and the factors which influence functional behaviours in schooling fish. Tank-based experiments investigated individual and population level lateralisation, schooling behaviour, and optic lobe asymmetry. Variation in direction and strength of lateralisation in individuals was found in juveniles, but at a population level significant bias was found in adults. Right eye biased fish had a larger right optic lobe than control fish. Strongly lateralised fish showed a tendency to occupy positions of safety within the school more frequently than control fish. In combination with observed differences in schooling behaviour, the possibility of ontogenetic plasticity in behavioural lateralisation and optic lobe morphology is suggested.     

Schooling Fish Under Attack Are Not All Equal: Some Lead,Others Follow

Animal groups such as fish schools, bird flocks and insect swarms appear to move so synchronously that they have long been considered egalitarian, leaderless units. In schooling fish, video observations of their spatial-temporal organization have, however, shown that anti-predator manoeuvres are not perfectly synchronous and that individuals have spatial preferences within the school. Nonetheless, when facing life-or-death situations, it is not known whether schooling fish react to a threat following a random or a hierarchically-based order. Using high-speed video analysis, here we show that schooling fish (Golden grey mullet, Liza aurata) evade a threat in a non-random order, therefore individuals that are first or last to react tend to do so repeatedly over sequential stimulations. Furthermore, startle order is strongly correlated with individual positional preferences. Because school members are known to follow individuals that initiate a manoeuvre, early responders are likely to exert the strongest influence on the escape strategy of the whole school. Our results present new evidence of the intrinsic heterogeneity among school members and provide new rules governing the collective motion of gregarious animals under predator attack.