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Results for “Animal Behavior and Cognition”

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bioRxiv2018

Learning to act by integrating mental simulations and physical experiments

People can learn about the effects of their actions either by performing physical experiments or by running mental simulations. Physical experiments are reliable but risky; mental simulations are unreliable but safe. We investigate how people negotiate the balance between these strategies. Participants attempted to shoot a ball at a target, and could pay to take practice shots (physical experiments). They could also simply think (run mental simulations), but were incentivized to act quickly by paying for time. We demonstrate that the amount of thinking time and physical experiments is sensitive to trial characteristics in a way that is consistent with a model that integrates information across simulation and experimentation and decides online when to perform each.

animal behavior and cognition↗

bioRxiv2018

Learning list concepts through program induction

Humans master complex systems of interrelated concepts like mathematics and natural language. Previous work suggests learning these systems relies on iteratively and directly revising a language-like conceptual representation. We introduce and assess a novel concept learning paradigm called Marthas Magical Machines that captures complex relationships between concepts. We model human concept learning in this paradigm as a search in the space of term rewriting systems, previously developed as an abstract model of computation. Our model accurately predicts that participants learn some transformations more easily than others and that they learn harder concepts more easily using a bootstrapping curriculum focused on their compositional parts. Our results suggest that term rewriting systems may be a useful model of human conceptual representations.

animal behavior and cognition↗

bioRxiv2018

Regulation of Harvester Ant Foraging as a Closed-Loop Excitable System

Ant colonies regulate activity in response to changing conditions without using centralized control. Harvester ant colonies forage in the desert for seeds, and their regulation of foraging manages a tradeoff between spending and obtaining water. Foragers lose water while outside in the dry air, but the colony obtains water by metabolizing the fats in the seeds they eat. Previous work shows that the rate at which an outgoing forager leaves the nest depends on its recent experience of brief antennal contact with returning foragers that carry a seed. We examine how this process can yield foraging rates that are robust to uncertainty and responsive to temperature and humidity across minutes to hour-long timescales. To explore possible mechanisms, we develop a low-dimensional analytical model with a small number of parameters that captures observed foraging behavior. The model uses excitability dynamics to represent response to interactions inside the nest and a random delay distribution to represent foraging time outside the nest. We show how feedback of outgoing foragers returning to the nest stabilizes the incoming and outgoing foraging rates to a common value determined by the \"volatility\" of available foragers. The model exhibits a critical volatility above which there is sustained foraging at a constant rate and below which there is cessation of foraging. To explain how the foraging rates of colonies adjust to temperature and humidity, we propose a mechanism that relies on foragers modifying their volatility after they leave the nest and get exposed to the environment. Our study highlights the importance of feedback in the regulation of foraging activity and points to modulation of volatility as a key to explaining differences in foraging activity in response to conditions and across colonies. Our results present opportunities for generalization to other contexts and systems with excitability and feedback across multiple timescales.\n\nAuthor SummaryWe investigate the collective behavior that allows colonies of desert harvester ants to regulate foraging activity in response to environmental conditions. We develop an analytical model connecting three processes: 1) the interactions between foragers returning to the nest and available foragers waiting inside the nest, 2) the effect of these interactions on the likelihood of available foragers to leave the nest to forage, and 3) the return of foragers to the nest after finding seeds. We propose a mechanism in which available foragers modify their response to interactions after their first exposure to the environment. We show how this leads to colony foraging rates that adjust to environmental conditions over time scales from minutes to hours. Our model may prove useful for studying resilience in other classes of systems with excitatory dynamics.

animal behavior and cognition↗

bioRxiv2018

Diverse incubation rhythms in a facultatively uniparental shorebird -- the Northern Lapwing

Incubation by both parents is the most common form of care for eggs. Although the involvement of the two parents may vary dramatically between and within pairs, as well as over the day and breeding season, detailed description of this variation (especially in species with variable male contribution to incubation) is rare. Here, we continuously video-monitored 113 nests of Northern Lapwing Vanellus vanellus over the breeding season to reveal the diversity of incubation rhythms and parental involvement. We found great between-nest variation in the overall nest attendance (68 -94%; median = 87%) and in how much males incubated (0 - 37%; median = 13%). Notably, the less the males incubated, the lower was the overall nest attendance, even though females partially compensated for the males decrease. Overall, incubation rhythms changed little over the season and incubation period. However, as nights shorten with the progressing breeding season, the female longest night incubation bout shortened too. Essentially, nest attendance was highest, incubation bouts longest, exchange gaps shortest and male involvement lowest during the night. Also, males tended to incubate the most after sunrise and before sunset. To conclude, we revealed strong circadian rhythms and remarkable between nest differences in Northern Lapwing incubation (especially in male involvement), yet despite seasonal environmental trends (e.g. increasing temperature) Lapwing incubation rhythms remained relatively stable over the season and incubation period.

animal behavior and cognition↗

bioRxiv2018

Absolute pitch can be learned by some adults

Absolute pitch (AP), the rare ability to name any musical note without the aid of a reference note, is thought to develop in an early critical period of development. Although recent research has shown that adults can improve AP abilities in a single training session, the best learners still did not achieve note classification performance comparable to performance of a genuine AP possessor. Here, we demonstrate that genuine AP levels of performance can be trained in eight weeks for some adults, with the best learner passing all measures of AP ability after training and retaining this knowledge for at least four months after training. Alternative explanations of these positive results, such as improving accuracy through adopting a slower, relative pitch strategy, are not supported based on joint analyses of response time and accuracy. The post-training AP assessments were extensive, totaling 204 notes taken from eight different timbres and spanning over seven octaves. These results clearly demonstrate that explicit perceptual training in some adults can lead to AP performance that is behaviorally indistinguishable from AP that results from childhood development. Implications for theories of AP acquisition are discussed.

animal behavior and cognition↗

bioRxiv2018

The effectiveness of clove oil and cautery disbudding methods on preventing horn growth in dairy goat kids

The effectiveness of clove oil and cautery disbudding on horn growth was evaluated in goat kids. The study used 243 Saanen doe kids (4{+/-}1.0 days old; mean {+/-} SD) on two commercial dairy goat farms, and were disbudded with either (i) clove oil injection (CLOVE), (ii) a cautery iron and bud removed (BUDOFF), or (iii) a cautery iron with bud left intact (BUDON). Each kid received a different treatment per bud, which were balanced between buds (left and right) and randomly allocated. A trained observer monitored bud growth following treatment for 3 months recording either: N: no growth, H: normal horn, S: abnormal horn (scur), or SC: soft, fibrous lump (scorn). After the final observation, buds were assessed for the probability of detecting (i) success (no growth), (ii) scurs, (iii) horns or (iv) scorns [with 95% CI]. The probability of success for BUDOFF (0.77 [0.63, 0.87]) was higher than for BUDON (0.20 [0.11, 0.34]) and CLOVE (0.09 [0.04, 0.18]; P [≤] 0.05). Furthermore, the probability of success for BUDON was higher than for CLOVE (P [≤] 0.05). The probability of scurs was higher for CLOVE (0.72 [0.63, 0.80]) than BUDOFF (0.25 [0.17, 0.34]) and BUDON (0.30 [0.21, 0.39]; P [≤] 0.05). There was no difference in the probability of scurs for BUDOFF and BUDON (P > 0.05). The probability of horns was higher for CLOVE (0.21 [0.15, 0.29]) than BUDON (0.02 [0.01, 0.06]; P [≤] 0.05); horns were not observed for BUDOFF. The probability of scorns for BUDON, the only treatment that led to scorns, was 0.41 (0.25, 0.60). These results suggest that BUDOFF was more effective at preventing growth than CLOVE and BUDON and appears the most effective method, of the methods tested, for disbudding kids. Future research should explore different clove oil administration methods or other alternatives to cautery disbudding that may be both efficacious and cause less pain.

animal behavior and cognition↗

bioRxiv2018

Hormonal signaling cascades required for phototaxis switch in wandering Leptinotarsa decemlineata larvae

Many animals exploit several niches sequentially during their life cycles, a fitness referred to as ontogenetic niche shift (ONS). To successfully accomplish ONS, transition between development stages is often coupled with changes in one or more primitive, instinctive behaviors. Yet, the underlining molecular mechanisms remain elusive. We show here that Leptinotarsa decemlineata larvae finish their ONS at the wandering stage by leaving the plant and pupating in soil. At middle wandering phase, larvae also switch their phototactic behavior, from photophilic at foraging period to photophobic. We find that enhancement of juvenile hormone (JH) signal delays the phototactic switch, and vise verse. Moreover, RNA interference (RNAi)-aided knockdown of LdPTTH (prothoracicotropic hormone gene) or LdTorso (PTTH receptor gene) impairs avoidance response to light, a phenotype nonrescuable by 20-hydroxyecdysone. Consequently, the RNAi beetles pupate at the soil surface or in shallow layer of soil, with most of them failing to construct pupation chambers. Furthermore, a combination of depletion of LdPTTH/LdTorso and disturbance of JH signal causes no additional effects on light avoidance response and pupation site. Finally, we establish that TrpA1 (transient receptor potential (TRP) cation channel) is necessary for light avoidance behavior, acting downstream of PTTH. We conclude that JH/PTTH cascade concomitantly regulates metamorphosis and the phototaxis switch, to drive ONS of the wandering beetles from plant into soil to start the immobile pupal stage.\n\nAuthor summaryMany animals occupy distinct niches and utilize diverse resources at different development stages in order to meet stage-dependent requirements and overcome stage-specific limitations. This fitness is referred to as ontogenetic niche shift (ONS). During the preparation for ONS, animals often change one or more primitive, instinctive behaviors. Holometabolous insects, with four discrete developmental periods usually in different niches, are a suitable animal group to explore the molecular modes of these behavioral switches. Here we find that Leptinotarsa decemlineata larvae, an insect defoliator of potatoes, switch their phototactic behavior, from photophilic at feeding period to photophobic during the larval-pupal transition (wandering stage). This phototactic switch facilitates the wandering larvae to accomplish the ONS from potato plant to their pupation site below ground. We show that JH/PTTH cascade controls the phototaxis switch, through a step in photo transduction between the photoreceptor molecule and the transient receptor potential cation channel.

animal behavior and cognition↗

bioRxiv2018

A rational account of human memory search

Performing everyday tasks requires the ability to search through and retrieve past memories. A central paradigm to study human memory search is the semantic fluency task, where participants are asked to retrieve as many items as possible from a category (e.g. animals). Observed responses tend to be clustered semantically. To understand when our mind decides to switch from one cluster/patch to the next, recent work has proposed two competing mechanisms. Under the first switching mechanism, people make strategic decision to switch away from a depleted patch based on marginal value theorem, similar to optimal foraging in a spatial environment. The second switching mechanism demonstrates that similar behavior patterns can emerge using a random walk on a semantic network, without necessarily involving strategic switches. In the current work, instead of comparing competing switching mechanisms over observed human data, we propose a rational account of the problem by examining what would be the optimal patch-switching policy under the framework of reinforcement learning. The reinforcement learning agent, a Deep Q-Network (DQN), is built upon the random walk model and allows strategic switches based on features of the local semantic patch. After learning from rewards, the resulted policy of the agent gives rise to a third switching mechanism, which outperforms the previous two switching mechanisms. Our results provide theoretical justification of strategies used in human memory research, and shed light on how an optimal AI agent under realistic human constraints can generate hypothesis about human strategies in the same task.

animal behavior and cognition↗

bioRxiv2018

Social learning strategies regulate the wisdom and madness of interactive online crowds

Why groups of individuals sometimes exhibit collective wisdom and other times maladaptive herding is an enduring conundrum. Here we show that this apparent conflict is regulated by the social learning strategies deployed. We examined the patterns of human social learning through an interactive online experiment with 699 participants, varying both task uncertainty and group size, then used hierarchical Bayesian model-ftting to identify the individual learning strategies exhibited by participants. Challenging tasks elicit greater conformity amongst individuals, with rates of copying increasing with group size, leading to high probabilities of herding amongst large groups confronted with uncertainty. Conversely, the reduced social learning of small groups, and the greater probability that social information would be accurate for less-challenging tasks, generated wisdom of the crowd effects in other circumstances. Our model-based approach provides evidence that the likelihood of collective intelligence versus herding can be predicted, resolving a longstanding puzzle in the literature.

animal behavior and cognition↗

bioRxiv2018

Carpenter ants use diverse antennae sampling strategies to track odor trails

Directed and meaningful animal behavior depends on the ability to sense key features in the environment. Among the different environmental signals, olfactory cues are critically important for foraging, navigation, and social communication in many species, including ants. Ants use their two antennae to explore the olfactory world, but how they do so remains largely unknown. In this study, we use high resolution videography to characterize the antennae dynamics of carpenter ants (Camponotus pennsylvanicus). Antennae are highly active during both tracking and exploratory behavior. When tracking, ants used several distinct behavioral strategies with stereotyped antennae sampling patterns (which we call sinusoidal behavior, probing, and trail following). In all behaviors, left and right antennae movements were anti-correlated, and tracking ants exhibited biases in the use of left vs right antenna to sample the odor trail. These results suggest non-redundant roles for the two antennae. In one of the behavioral modules (trail following), ants used both antennae to detect trail edges and direct subsequent turns, suggesting a specialized form of tropotaxis. Lastly, removal of an antenna resulted not only in less accurate tracking but also in changes in the sampling pattern of the remaining antenna. Our quantitative characterization of odor trail tracking lays a foundation to build better models of olfactory sensory processing and sensorimotor behavior in terrestrial insects.\n\nSummary StatementHigh resolution imaging of antennae reveals distinct patterns of sampling with non-redundant roles in odor tracking.

animal behavior and cognition↗

bioRxiv2018

Searching for rewards like a child means less generalization and more directed exploration

How do children and adults differ in their search for rewards? We consider three different hypotheses that attribute developmental differences to either childrens increased random sampling, more directed exploration towards uncertain options, or narrower generalization. Using a search task in which noisy rewards are spatially correlated on a grid, we compare 55 younger children (age 7-8), 55 older children (age 9-11), and 50 adults (age 19-55) in their ability to successfully generalize about unobserved outcomes and balance the exploration-exploitation dilemma. Our results show that children explore more eagerly than adults, but obtain lower rewards. Building a predictive model of search to disentangle the unique contributions of the three hypotheses of developmental differences, we find robust and recoverable parameter estimates indicating that children generalize less and rely on directed exploration more than adults. We do not, however, find reliable differences in terms of random sampling.

animal behavior and cognition↗

bioRxiv2018

Small females prefer small males: size assortative mating in Aedes aegypti mosquitoes

With Aedes aegypti mosquitoes now being released in field programs aimed at disease suppression, there is interest in identifying factors influencing the mating and invasion success of released mosquitoes. One factor that can increase release success is size: released males may benefit competitively from being larger than their field counterparts. However, there could be a risk in releasing only large males if small field females avoid these males and instead prefer small males. Here we investigate this risk by evaluating mating success for mosquitoes differing in size. We measured mating success indirectly by coupling size with Wolbachia-infected or uninfected mosquitoes and scoring cytoplasmic incompatibility as a way of estimating relative mating success. Large females showed no evidence of a mating preference, whereas small males were relatively more successful than large males when mating with small females, exhibiting an advantage of around 20-25%. Because field females typically encompass a wide range of sizes while laboratory reared (and released) males typically fall into a narrow size range of large mosquitoes, these patterns can influence the success of release programs which rely on cytoplasmic incompatibility to suppress populations and initiate replacement invasions. Releases could include some small males generated under low food or crowded conditions to counter this issue, although this would need to be weighed against issues associated with costs of producing males of various size classes.

animal behavior and cognition↗

bioRxiv2018

Stepping into a dangerous quagmire: environmental determinants of human-lancehead pit vipers (Bothrops genus) contact resulting in injuries, Brazilian Amazon

Despite significant and successful efforts in Brazil regarding snakebites in the areas of research, antivenom manufacture and quality control, training of health professionals in the diagnosis and clinical management of bites, little is known about determinants of snakebites incidence in order to further plan interventions to reduce the impact of this medical condition. Understanding the complexity of ecological interactions in a geographical region is important for prediction, prevention and control measures of snakebites. The aim of this investigation is to describe spatial distribution and identify environmental determinants of human- lancehead pit vipers (Bothrops genus) contact resulting in injuries, in the Brazilian Amazon. Aggregated data by municipality was used to analyze the spatial distribution of Bothrops bites cases and its relationship with geographic and environmental factors. Eight geo-environmental factors were included in the analysis as independent variables: (1) tree canopy loss increase; (2) area with vegetation cover; (3) area covered by water bodies; (4) altitude; (5) precipitation; (6) air relative humidity; (7) soil moisture; and (8) air temperature. Human- lancehead pit vipers (Bothrops genus) contact resulting in envenomings in the Amazon region is more incident in lowlands [-0.0006827 (IC95%: -0.0007705; - 0.0005949), p<0.0001], with high preserved original vegetation cover [0.0065439 (IC95%: 0.0070757; 0.0060121), p<0.0001], with heaviest rainfall [0.0000976 (IC95%: 0.0000925; 0.0001026), p<0.0001] and higher air relative humidity [- 0.0081773 (IC95%: -0.0107681; -0.0055865), p<0.0001]. This association is interpreted as the result of the higher forest productivity and abundance of pit vipers in such landscapes.\n\nAuthor summaryDespite successful efforts in Brazil regarding snakebites in the areas of research, antivenom manufacture and quality control and training of health professionals, little is known about determinants of snakebites incidence in order to further plan interventions to reduce the impact of this medical condition. Understanding the complexity of ecological interactions in a geographical region is important for prediction, prevention and control measures of snakebites. The aim of this study is to describe spatial distribution and identify environmental determinants of human- lancehead pit vipers (Bothrops genus) contact resulting in injuries, in the Brazilian Amazon. An increase in the forest productivity with a higher availability of some types of prey, such as frogs and amphibians, anurans and lizards, was suggested as a cause for the higher snake abundance in the rainy season. Probably due to the higher forest productivity and abundance of pit vipers in such landscapes, human-lancehead pit vipers contact resulting in envenomings in the Amazon region is more incident in lowlands, with high preserved original vegetation cover, with heaviest rainfall and higher air relative humidity.

animal behavior and cognition↗

bioRxiv2018

Customizing material into embodied cap by sponge crab

Animal personality is considered to be developed through complex interactions of an individual with its surrounding environment. How can we quantify the personality of an individual? Quantifying intra- and inter-individual variability of behavior, or individual behavioral type, appears to be a prerequisite in the study of animal personality. We propose a statistical method from a predictive point of view to measure the appropriateness of our assumption of individual behavior in repeatedly measured behavioral data from several individuals. For a model case, we studied the sponge crab Lauridromia dehaani known to make and carry a cap from a natural sponge for camouflage. Because a cap is most likely to be rebuilt and replaced repeatedly, we hypothesized that each individual crab would grow a unique behavioral type and it would be observed under an experimentally controlled environmental condition. To test the hypothesis, we conducted behavioral experiments and employed a new Bayesian model-based comparison method to examine whether crabs have individual behavioral types in the cap making behavior. Crabs were given behavioral choices by using artificial sponges of three different sizes. We modeled the choice of sponges, size of the trimmed part of a cap, size of the cavity of a cap, and the latency to produce a cap, as random variables in 26 models, including hierarchical models specifying the behavioral types. In addition, we calculated the marginal-level widely applicable information criterion (mWAIC) values for hierarchical models to evaluate and compared them with the non-hierarchical models from the predictive point of view. As a result, the crabs of less than about 9 cm in size were found to make caps from the sponges. The body size explained the behavioral variables namely, choice, trimmed cap characteristics, and cavity size, but not latency. Furthermore, we captured the behavioral type as a probabilistic distribution structure of the behavioral data by comparing WAIC. Our statistical approach is not limited to behavioral data but is also applicable to physiological or morphological data when examining whether some group structure exists behind fluctuating empirical data.

animal behavior and cognition↗

bioRxiv2018

Fast animal pose estimation using deep neural networks

Recent work quantifying postural dynamics has attempted to define the repertoire of behaviors performed by an animal. However, a major drawback to these techniques has been their reliance on dimensionality reduction of images which destroys information about which parts of the body are used in each behavior. To address this issue, we introduce a deep learning-based method for pose estimation, LEAP (LEAP Estimates Animal Pose). LEAP automatically predicts the positions of animal body parts using a deep convolutional neural network with as little as 10 frames of labeled data for training. This framework consists of a graphical interface for interactive labeling of body parts and software for training the network and fast prediction on new data (1 hr to train, 185 Hz predictions). We validate LEAP using videos of freely behaving fruit flies (Drosophila melanogaster) and track 32 distinct points on the body to fully describe the pose of the head, body, wings, and legs with an error rate of <3% of the animals body length. We recapitulate a number of reported findings on insect gait dynamics and show LEAPs applicability as the first step in unsupervised behavioral classification. Finally, we extend the method to more challenging imaging situations (pairs of flies moving on a mesh-like background) and movies from freely moving mice (Mus musculus) where we track the full conformation of the head, body, and limbs.

animal behavior and cognition↗

bioRxiv2018

The effect of nutrient storage on courtship behavior and copulation frequency in the fruit fly, Drosophila melanogaster.

Nutrient storage and metabolism effects on reproductive behavior are well studied in higher vertebrates like mammals, but are less understood in simpler systems. Drosophila melanogaster is well suited to study the ramifications of diet and metabolic energy storage on reproductive behaviors as they are commonly used to explore energy mobilization pathways. We tested, for the first time, courtship of the naturally occurring adipose (adp60) mutant which over-accumulates triglycerides and glycogen on a normal diet. We also fed wild type (WT) flies either a normal diet, high fat diet or food deprived them before measuring courtship, copulations, and glycogen and triglyceride levels. Adipose mutants decreased both courtship and copulation frequency, yet showed the highest glycogen and triglyceride levels. We suggest the adp60 physique and/or an altered ability to utilize mobilize energy explains these effects. Food deprived WT flies had the lowest glycogen and triglycerides but exhibited shortened courtship latencies with increased courtship behaviors. This may be due to a decreased lifespan of food deprived flies leading to a greater reproductive drive. However, high fat fed flies copulated more frequently and had the highest triglycerides among WT groups, yet equal glycogen levels to the normal fed WT group. Thus, a high fat diet either increases male attractivity or male courtship persistence. Taken together, available diet and nutrient storage affects male fly reproductive behavior in a unique manner, which may be explained by their natural history, and provides a paradigm for understanding energetics based on reproductive potential.

animal behavior and cognition↗

bioRxiv2018

Human vicarious trial and error is predictive of spatial navigation performance

When learning new environments, rats often pause at decision points and look back and forth over their possible trajectories as if they were imagining the future outcome of their actions, a behavior termed \"Vicarious trial and error\" (VTE). As the animal learns the environmental configuration, rats change from deliberative to habitual behavior, and VTE tends to disappear, suggesting a functional relevance in the early stages of learning. Despite the extensive research on spatial navigation, learning and VTE in the rat model, fewer studies have focused on humans. Here, we tested whether head-scanning behaviors that humans typically exhibit during spatial navigation are as predictive of spatial learning as in the rat. Subjects performed a goal-oriented virtual navigation task in a symmetric environment. Spatial learning was assessed through the analysis of trajectories, timings, and head orientations, under habitual and deliberative spatial navigation conditions. As expected, we found that trajectory length and duration decreased with the trial number, implying that subjects learned the spatial configuration of the environment over trials. Interestingly, IdPhi (a standard metric of VTE) also decreased with the trial number, suggesting that humans benefit from the same head-orientation scanning behavior as rats at spatial decision-points. Moreover, IdPhi captured exclusively at the first decision-point of each trial, was correlated with trial trajectory duration and length. Our findings demonstrate that in VTE is a signature of the stage of spatial learning in humans, and can be used to predict performance in navigation tasks with high accuracy.

animal behavior and cognition↗

bioRxiv2018

Utilising the boundary layer to help restore the connectivity of fish habitats and populations

SignificanceHabitat fragmentation is a significant contributor to the worldwide decline of freshwater ecosystem health, the most pervasive cause of which is culverts. Culverts act as a barrier to fish movement, impacting feeding, predator avoidance, spawning, and community structures. Here we show that a common remediation strategy that involves baffles, is detrimental to the successful passage of small bodied and juvenile fish at high velocities. To remedy this widespread problem, we present a novel remediation design that benefits a range of small-bodied species and juvenile fish at the same high velocities, regardless of morphology or ecological niche. The application of this remediation design may be expanded to any smooth surfaced anthropogenic structure, to improve fish passage and restore ecosystem functionality.\n\nAbstractCulverts are a major cause of habitat fragmentation in freshwater ecosystems, are a barrier to fish movement, and are regarded as a significant contributor in the decline of freshwater fish populations globally. To try to address this, various culvert remediation designs have been implemented, including the installation of vertical baffles and the provision of naturalistic (rock) substrates. While remediation strategies generally aim to reduce the velocity of water flowing through the structure, there is often resistance to their use because the resultant reduction in culvert discharge can negatively impact upstream flooding while also resulting in debris clogging and increased culvert maintenance costs. In addition, baffles markedly increase water turbulence that may be detrimental to passage by some fish species or size classes. Here we present some novel remediation designs that exploit the reduced water velocity in boundary layers along the culvert wall to enhance fish passage without significantly compromising discharge capacity. These longitudinal designs produce an expanded reduced velocity zone along the culvert margins that generate minimal turbulence. We show that these novel designs are significantly advantageous to the swimming endurance and traversability for six small-bodied Australian fish species. We also provide data on how and why some culvert baffle designs may impede small-bodied fish passage. This data scales with increasing water velocity, encompassing inter-specific differences in swimming capacity. These results have broad implications for fish community structure and the requirement of juvenile cohort of large-bodied commercially important species where baffles have been implemented to facilitate fish passage.

animal behavior and cognition↗