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Anthropogenic noise is a pervasive pollutant that decreases environmental quality by disrupting a suite of behaviors vital to perception and communication. However, even within populations of noise-sensitive species, individuals still select breeding sites located within areas exposed to high noise levels, with largely unknown physiological and fitness consequences. We use a study system in the natural gas fields of northern New Mexico to test the prediction that exposure to noise causes glucocorticoid-signaling dysfunction and decreases fitness in a community of secondary cavity-nesting birds. In accordance with these predictions, and across all species, we find strong support for noise exposure decreasing baseline corticosterone in adults and nestlings and, conversely, increasing acute stressor-induced corticosterone in nestlings. We also document fitness consequences with increased noise in the form of reduced hatching success in the western bluebird (Sialia mexicana), the species most likely to nest in noisiest environments. Nestlings of all three species exhibited accelerated growth of both feathers and body size at intermediate noise amplitudes compared with lower or higher amplitudes. Our results are consistent with recent experimental laboratory studies and show that noise functions as a chronic, inescapable stressor. Anthropogenic noise likely impairs environmental risk perception by species relying on acoustic cues and ultimately leads to impacts on fitness. Our work, when taken together with recent efforts to document noise across the landscape, implies potential wide-spread, noise-induced chronic stress coupled with reduced fitness for many species reliant on acoustic cues.

Decades of research demonstrate that roads impact wildlife and suggest traffic noise as a primary cause of population declines near roads. We created a “phantom road” using an array of speakers to apply traffic noise to a roadless landscape, directly testing the effect of noise alone on an entire songbird community during autumn migration. Thirty-one percent of the bird community avoided the phantom road. For individuals that stayed despite the noise, overall body condition decreased by a full SD and some species showed a change in ability to gain body condition when exposed to traffic noise during migratory stopover. We conducted complementary laboratory experiments that implicate foraging-vigilance behavior as one mechanism driving this pattern. Our results suggest that noise degrades habitat that is otherwise suitable, and that the presence of a species does not indicate the absence of an impact.

Correctly assessing the total impact of predators on prey population growth rates (lambda, λ) is critical to comprehending the importance of predators in species conservation and wildlife management. Experiments over the past decade have demonstrated that the fear (antipredator responses) predators inspire can affect prey fecundity and early offspring survival in free-living wildlife, but recent reviews have highlighted the absence of evidence experimentally linking such effects to significant impacts on prey population growth. We experimentally manipulated fear in free-living wild songbird populations over three annual breeding seasons by intermittently broadcasting playbacks of either predator or nonpredator vocalizations and comprehensively quantified the effects on all the components of population growth, together with evidence of a transgenerational impact on offspring survival as adults. Fear itself significantly reduced the population growth rate (predator playback mean λ = 0.91, 95% CI = 0.80 to 1.04; nonpredator mean λ = 1.06, 95% CI = 0.96 to 1.16) by causing cumulative, compounding adverse effects on fecundity and every component of offspring survival, resulting in predator playback parents producing 53% fewer recruits to the adult breeding population. Fear itself was consequently projected to halve the population size in just 5 years, or just 4 years when the evidence of a transgenerational impact was additionally considered (λ = 0.85). Our results not only demonstrate that fear itself can significantly impact prey population growth rates in free-living wildlife, comparing them with those from hundreds of predator manipulation experiments indicates that fear may constitute a very considerable part of the total impact of predators.

Background Interspecific interactions, including competition and predation, are key drivers of ecological systems. Understanding these interactions remains challenging in the wild as it requires quantifying their effects, particularly the non-consumptive effects (NCEs) driven by predation risk. We conducted a 7-month study in a semi-natural open bat colony, monitoring interactions between Egyptian fruit bats ( Rousettus aegyptiacus ) and black rats ( Rattus rattus ) competing for food, where rats also pose a potential predation risk to the bats. Results Video analysis revealed that bat responses to rats were fundamentally different from responses to conspecifics. The primary response was avoidance, with bat landings near food decreasing significantly when rats were present. For the 789 landings that did occur, bats showed increased vigilance and reduced foraging success, demonstrating clear NCEs. Crucially, bat foraging strategies were highly context-dependent, shifting with seasonal resource availability and rat abundance. During winter when rats were uncommon, the bats primarily employed predation risk-averse strategies (avoidance and vigilance). In spring, when rats were frequent, although there was clear temporal partitioning between the bat and the rat populations, some of the bats shifted to heterospecific interference competition, and occasionally attacked the rats to gain access to food—a behavior inconsistent with simple risk-aversion models. Conclusions Our findings demonstrate that the bat-rat interactions are dynamically modulated by resource availability, which alters rat presence and thereby the context-dependent interplay between interference competition and NCEs. This study provides rare quantitative evidence of how behaviorally flexible animals strategically manage interference competition and predation risk based on seasonal ecological conditions.

Fear itself (perceived predation risk) can affect wildlife demography, but the cumulative impact of fear on population dynamics is not well understood. Parental care is arguably what most distinguishes birds and mammals from other taxa, yet only one experiment on wildlife has tested fear effects on parental food provisioning and the repercussions this has for the survival of dependent offspring, and only during early-stage care. We tested the effect of fear on late-stage parental care of mobile dependent offspring, by locating radio-tagged Song Sparrow fledglings and broadcasting predator or non-predator playbacks in their vicinity, measuring their parent’s behavior and their own, and tracking the offspring’s survival to independence. Fear significantly reduced late-stage parental care, and parental fearfulness (as indexed by their reduction in provisioning when hearing predators) significantly predicted their offspring’s condition and survival. Combining results from this experiment with that on early-stage care, we project that fear itself is powerful enough to reduce late-stage survival by 24%, and cumulatively reduce the number of young reaching independence by more than half, 53%. Experiments in invertebrate and aquatic systems demonstrate that fear is commonly as important as direct killing in affecting prey demography, and we suggest focusing more on fear effects and on offspring survival will reveal the same for wildlife.

Summary Escaping from a predator is a matter of life or death, and prey are expected to adaptively alter their physiology under chronic predation risk in ways that may affect escape. Theoretical models assume that escape performance is mass dependent, whereby scared prey strategically maintain an optimal body mass to enhance escape. Experiments testing the mass‐dependent predation risk hypothesis have demonstrated that prior experience of predation risk can affect body mass, and the behavioural decisions about evasive actions to take. Other studies on natural changes in body mass indicate that mass can affect escape. No single experiment has tested if all of these components are indeed linked, which is a critical necessary condition underpinning the mass‐dependent predation risk hypothesis. We tested all components of the mass‐dependent predation risk hypothesis in a repeated measures experiment by presenting predator and non‐predator cues to brown‐headed cowbirds housed in semi‐natural conditions. Exposure to predator cues affected body mass, fat, pectoral muscle thickness and evasive actions (take‐off angle and speed), but not the physiological capacity to escape, as measured by flying ability. Examining individual variation revealed that flying ability was unrelated to mass loss in either sex, unrelated to mass gain in males, and only females that gained a very large amount of mass flew poorly. We next conducted a body mass manipulation in the laboratory to rigorously test whether small to large perturbations in mass can ever affect flying ability. We induced either no change in mass (control), a moderate reduction of <10% or a more extreme reduction of >10% which the literature suggests should enhance flight. Flying ability was maintained regardless of treatment. Examining individual variation revealed the same precise patterns as in the first experiment. We conclude that prey may alter their mass and evasive actions in response to predation risk, but their escape ability remains robust and inelastic, presumably because disabling oneself is likely to lead to disastrous consequences. We suggest that animals may only face a mass‐dependent predation risk trade‐off in a narrow set of circumstances linked to life‐history stages that require large amounts of mass gain, for example, parturition and migration. A lay summary is available for this article. Lay Summary

Spatial and temporal variation in perceived predation risk is an important determinant of movement and foraging activity of animals. Foraging in this landscape of fear, individuals need to decide where and when to move, and what resources to choose. Foraging theory predicts the outcome of these decisions based on energetic trade‐offs, but complex interactions between perceived predation risk and preferences of foragers for certain functional traits of their resources are rarely considered. Here, we studied the interactive effects of perceived predation risk on food trait preferences and foraging behavior in bank voles (Myodes glareolus) in experimental landscapes. Individuals (n = 19) were subjected for periods of 24 h to two extreme, risk‐uniform landscapes (either risky or safe), containing 25 discrete food patches, filled with seeds of four plant species in even amounts. Seeds varied in functional traits: size, nutrients, and shape. We evaluated whether and how risk modifies forager preference for functional traits. We also investigated whether perceived risk and distance from shelter affected giving‐up density (GUD), time in patches, and number of patch visits. In safe landscapes, individuals increased time spent in patches, lowered GUD and visited distant patches more often compared to risky landscapes. Individuals preferred bigger seeds independent of risk, but in the safe treatment they preferred fat‐rich over carb‐rich seeds. Thus, higher densities of resource levels remained in risky landscapes, while in safe landscapes resource density was lower and less diverse due to selective foraging. Our results suggest that the interaction of perceived risk and dietary preference adds an additional layer to the cascading effects of a landscape of fear which affects biodiversity at resource level. Animals need to make a lot of decisions when foraging on landscapes of fear, but complex interactions between perceived predation risk and dietary preferences are seldom studied. We studied the interaction of perceived predation risk, food trait preference and movement in experimental landscapes, and found that risky conditions lowered foraging time and density of resources. Individuals were opportunistic when feeding regardless of risk, but changed preference for certain food items when conditions were safe, adding an additional layer to cascading effects of landscapes of fear.

Herbivores making space use decisions must consider the trade-off between perceived predation risk and forage quality. Herbivores, specifically snowshoe hares (Lepus americanus), must constantly navigate landscapes that vary in predation risk and food quality, providing researchers with the opportunity to explore the factors that govern their foraging decisions. Herein, we tested predictions that intersect the risk allocation hypothesis (RAH) and optimal foraging theory (OFT) in a spatially explicit ecological stoichiometry framework to assess the tradeoff between predation risk and forage quality. We used individual and population estimates of snowshoe hare (n = 29) space use derived from biotelemetry across three summers. We evaluated resource forage quality for lowbush blueberry (Vaccinium angustifolium), a common and readily available forage species within our system, using carbon:nitrogen and carbon:phosphorus ratios. We used habitat complexity to proxy perceived predation risk. We analyzed how forage quality of blueberry, perceived predation risk, and their interaction impact the intensity of herbivore space use. We used generalized mixed effects models, structured to enable us to make inferences at the population and individual home range level. We did not find support for RAH and OFT. However, variation in the individual-level reactions norms in our models showed that individual hares have unique responses to forage quality and perceived predation risk. Our finding of individual-level responses indicates that there is fine-scale decision-making by hares, although we did not identify the mechanism. Our approach illustrates spatially explicit empirical support for individual behavioral responses to the food quality–predation risk trade-off.

Although ecologists have long recognized that animal space use is primarily determined by the presence of predators and the distribution of resources, the effects of these two environmental conditions have never been quantified simultaneously in a single spatial model. Here, in a novel approach, predator-specific landscapes of fear are constructed on the basis of behavioral responses of a prey species (vervet monkey; Cercopithecus aethiops), and we show how these can be combined with data on resource distribution to account for the observed variation in intensity of space use. Results from a mixed regressive—spatial regressive analysis demonstrate that ranging behavior can indeed be largely interpreted as an adaptive response to perceived risk of predation by some (but not all) predators and the spatial availability of resources. The theoretical framework behind the model is furthermore such that it can easily be extended to incorporate the effects of additional factors potentially shaping animal range use and thus may be of great value to the study of animal spatial ecology.

There is increasing interest in how animals respond to multiple stressors, including potential synergistic or antagonistic interaction between pathogens and perceived predation risk (PPR). For prey that exhibit phenotypic plasticity, it is unclear whether infection and PPR affect behaviour and morphology independently, or in an antagonistic or synergistic manner. Using a 2 × 2 factorial experiment involving green frog (Lithobates clamitans) tadpoles exposed to ranavirus (FV3) and larval dragonflies (Anax spp.), we assessed whether anti-predator responses were affected by infection. We found that activity and feeding were reduced additively by both stressors. Body mass of tadpoles from FV3-exposed tanks was lighter relative to control and PPR-only tanks, while metabolism was comparable across treatments. We found that FV3 exposure compromised morphometric responses to PPR in an antagonistic manner: tadpoles exposed to both treatments had restricted changes in tail depth compared to those receiving singular treatment. We conclude that multiple stressors can have complex and substantive effects on organisms, and that interactions between stressors may yield a range of responses depending on the level of exposure and sensitivity of the organism. Additional work should more fully determine mechanisms underlying the complex interplay between infection and predation risk, across a range of environmental conditions.