Indirect effects of hunting on wildlife

Hunting is more than the removal of individuals from wildlife populations. One of the classic examples comes from work on North American ungulates, where selective trophy hunting of large-horned bighorn sheep Ovis canadensis males has driven evolutionary declines in horn size and body mass (Coltman et al. 2003), illustrating how human-imposed selective pressures can restructure life-history traits. Yet growing evidence shows that hunting influences wildlife through far broader, non-lethal pathways. Studies on elk Cervus canadensis in human-dominated landscapes showed that human disturbance – especially hunting – can elevate vigilance more strongly than natural predators, reducing feeding time and potentially affecting fitness (Ciuti et al. 2012a). More recently, Zenth et al. (2025a) emphasized that wildlife responses to humans fall along an avoidance–tolerance–attraction continuum, shaped jointly by a species' evolutionary history with humans and by the ecological experiences individuals acquire over their lifetimes. In systems where humans behave primarily as predators, such as through hunting or persecution, responses are expected to shift strongly toward avoidance (Zenth et al. 2025a). This perspective aligns closely with the risk–disturbance hypothesis, which posits that animals perceive and respond to human activities much as they would to natural predators (Frid and Dill 2002). Under this framework, wildlife behavioral decisions emerge from an inherent trade-off between risk avoidance and other fitness-enhancing activities such as food acquisition and reproduction (Clinchy et al. 2016). Heightened anti-predator responses, even to ostensibly non-threatening forms of human disturbance, can impose high fitness costs. It is therefore unsurprising that many hunted species perceive humans as super-predators (Darimont et al. 2015), reacting to them in ways remarkably similar to reactions to large carnivores. The perception of risk induced by hunting may cascade into shifts in life-history traits even when no mortality occurs, and such effects can arise even in the absence of active hunting because many species treat human presence – whether hunters or not – as a potential threat (Zanette and Clinchy 2020). These indirect effects arise because hunting functions as a powerful ecological signal that can drive changes in physiological state, behaviour and spatial ecology. Despite their importance, indirect effects of hunting remain under-recognized in management frameworks (Cromsigt et al. 2013), where long-term harvest quotas and abundance estimates are often prioritized over behavioral and physiological responses. Yet as recreational activities grow and human land use becomes increasingly pervasive, wildlife populations are exposed to a mosaic of human presence, ranging from hikers to hunters, and indirect effects are becoming increasingly consequential for both conservation and sustainable harvest strategies. This special issue of Wildlife Biology brings together a diverse collection of studies that, collectively, illustrate many pathways through which hunting can influence wildlife beyond direct mortality. The contributions examine the physiological, behavioral, spatial, and demographic responses that emerge when animals navigate landscapes shaped by human predation risk. Some of these responses unfold at fine spatial and temporal scales, while others propagate across entire landscapes. By spanning different taxa, ecosystems and methodological approaches, the special issue provides a broad and integrative perspective on the mechanisms underlying indirect hunting effects. The contributions highlight not only the taxonomic and ecological breadth of these responses, but also the methodological diversity required to study them – from endocrinology and behavioral assays to experimental and observational surveys and GPS telemetry. Taken together, they offer a foundation for integrating indirect effects into management frameworks, encouraging a shift from viewing hunting solely as a source of mortality to understanding it as a multifaceted ecological force that requires explicit consideration in contemporary wildlife management. Among the most direct demonstrations of indirect effects is the elevation of physiological stress triggered by hunting activity. One of the earliest empirical studies on this topic showed that red deer Cervus elaphus hunted with hounds experienced profound physiological disruption, including depleted muscle glycogen, tissue damage, and extremely high cortisol concentrations, signs of severe physiological stress (Bateson and Bradshaw 1997). In this issue, Pedersen et al. (2024) report that mountain hares Lepus timidus pursued by hounds exhibit serum cortisol levels more than six times higher than hares shot without pursuit. Despite involving different taxa and contexts, these studies converge on the same conclusion: pursuit-based hunting can impose substantial physiological costs, and endocrine responses offer a sensitive metric for detecting disturbance even when demographic effects are not yet apparent. Such findings echo long-standing theoretical predictions that repeated activation of the stress axis can have downstream consequences for immune function, energy balance and reproductive output (Crespi et al. 2013). Behaviour provides one of the earliest indications of how animals perceive and react to disturbance. Vigilance and flight behavior are among the most widely studied responses, as they reflect an animal's assessment of potential danger and can impose opportunity costs. Across a range of taxa, hunting has been linked to increased vigilance and elevated flight-initiation distances (Pauli and Buskirk 2007, Tarakini et al. 2014), thereby shaping the landscape of fear and modifying access to key resources such as feeding and resting sites (Laundré et al. 2010). Fear-driven behavioral adjustments may translate into demographic costs (LaManna and Martin 2016), contributing to the broader suite of indirect effects associated with hunting pressure. Several papers in this special issue align with these results. In mallards Anas platyrhynchos, Blake-Bradshaw et al. (2024) experimentally manipulated different disturbance types (pedestrians and vehicles) and show that behavioral responses are highly context-dependent. Movement, diel activity and space use vary not only across disturbance types but also across hunting periods: for instance, pedestrians elicit stronger behavioral shifts outside the hunting season, whereas uncovered vehicles alter space use primarily in pre-hunt and early-hunt periods. These findings highlight how animals integrate risk at multiple spatial and temporal scales, weighing localized, non-lethal threats against the broader landscape-level risk imposed by hunting. Rock ptarmigan Lagopus muta behavior offers a striking complement. Sooth et al. (2025) quantify flight-initiation distance (FID) across hunted and unhunted populations in Iceland and Italy, showing that hunting triggers sharp increases in FID at the start of the hunting season, with rapid relaxation once hunting ends. These patterns illustrate the potential immediacy and reversibility of behavioral response to hunting risk. A related but more complex pattern emerges in Alpine marmots Marmota marmota. Zenth et al. (2025b) show that marmots in hunted areas have higher FID than those in recreation-only landscapes, indicating stronger avoidance of lethal disturbance. Unlike ptarmigan, however, marmots do not promptly adjust their behavior across the hunting season, and FIDs remain high also outside of the hunting season. Taken together, these studies do not point to a single behavioral response to hunting but rather to a spectrum of strategies: in some contexts, species exhibit rapid, reversible adjustments to risk and readily habituate to benign human presence, whereas in others they show more persistent avoidance of hunting risk, reflecting context-dependent differences in ecology, cognition and in their behavioral plasticity to update risk cues. Habitat selection and movement patterns are shaped by several factors: not only food availability, terrain and weather, but also human activities, which can alter habitat attractiveness, disrupt activity rhythms and generate landscapes of fear (Laundré et al. 2010). Hunting is particularly influential in this respect. By adding lethal risk to the landscape, it can induce shifts in diel activity, reduce use of certain areas at certain times of day, trigger refuge-seeking behavior or increase displacement as animals attempt to avoid hunters (Grignolio et al. 2011). Movement ecology therefore offers a powerful lens for understanding the indirect effects of hunting, because animals continually adjust where and when they move in response to perceived risk. Yet species differ markedly in how they navigate these trade-offs, and the contributions in this special issue illustrate this diversity of responses particularly well. Several studies show how hunting drives variation in movement ecology at local and landscape scales. In their long-term GPS analysis of alpine reindeer Rangifer tarandus, Mysterud et al. (2025) show that movements increase in years with higher harvest rates, particularly in late September when hunting pressure intensifies. Reindeer – living in open terrain and forming large, cohesive groups – exhibited longer and more variable step lengths during the daytime, as well as elevated movement on weekends early in the season. These patterns stand in contrast to those observed in red deer Cervus elaphus: Eggers et al. (2025) document strong day/night habitat segregation in forested landscapes, with deer in hunted areas reducing daytime movement and retreating into dense cover, before re-entering open habitats at night, when no hunting occurs. Together, these studies highlight that large herbivores differ markedly in their behavioral responses to hunting depending on habitat structure and social organization. Whereas forest ungulates often minimize movement to avoid detection during risky periods, open-habitat species such as reindeer may exhibit elevated movement and broader spatial displacement, potentially amplifying the energetic costs of disturbance at a critical time of year. Spatial redistribution is particularly pronounced in waterbirds. Tronel et al. (2025) show that abundance of waterbird communities declines sharply in hunted wetlands immediately after the hunting season opens, with birds concentrating in the limited network of available reserves. Such large-scale redistribution can effectively create a net loss of usable habitat, reducing the carrying capacity of wetlands and intensifying competition for food and resting opportunities even when suitable habitat is technically available. This may have consequences not only for conservation but also for hunting itself, as declining bird numbers may diminish hunting opportunities. These patterns highlight the need for management approaches that consider how hunting regulations, refuge networks and habitat management interact to support both conservation and sustainable hunting, while minimizing unintended ecosystem-level consequences. The direct demographic impacts of hunting operate through the removal of individuals from a population, reducing abundance, altering age and sex structure, and potentially influencing reproductive output and survival through harvest-selective pressures (Coltman et al. 2003, Milner et al. 2006, van de Walle et al. 2021). More subtle, however, are the indirect demographic consequences that arise when hunting modifies physiology, behaviour or space use in ways that ultimately affect vital rates (Frank et al. 2017). Elevated vigilance can reduce foraging efficiency and body condition, potentially lowering survival and reproductive success (Pauli and Buskirk 2007). Avoidance of high-quality foraging areas due to hunting risk may similarly impose nutritional constraints, particularly in species facing strong seasonal energetic bottlenecks (Bonnot et al. 2013), with possible carry-over effects on condition-dependent traits such as survival or recruitment. Indirect demographic responses can also emerge through behavior-dependent mortality, whereby individuals with certain movement or habitat-selection strategies are more likely to be harvested. In southern Sweden, where moose Alces alces experience high annual harvest rates, Graf et al. (2025) show that habitat selection predicts harvest risk in a sex-specific manner: males selecting high-NDVI areas during the rut were more likely to be shot, whereas female mortality increased among individuals selecting habitats closer to roads during the hunting season. These patterns suggest that hunting might impose selection on behavioral traits, gradually filtering habitat-use strategies within populations and creating demographic consequences that extend beyond direct removals. Notably, not all hunting-associated activities produce negative indirect effects. In northern bobwhite Colinus virginianus, Magdziuk et al. (2025) evaluate demographic outcomes of low-intensity dog training and find no adverse effects on adult or nest survival, clutch size, hatchability or fecundity. Rather than contradicting evidence for indirect effects, this study highlights their context dependence: disturbance intensity, frequency, habitat quality and management practices can determine whether behavioral or physiological responses translate into demographic consequences. In this system, well-managed land, predictable disturbance schedules and limited dog–bird encounters appear sufficient to buffer populations from sub-lethal effects, underscoring the need to avoid generalizing indirect effects across species or management contexts. While a special issue serves to advance knowledge through new empirical evidence, it also provides a vital platform for researchers to synthesize current findings and establish a cohesive agenda for future inquiry. This special issue shows that the ecological footprint of hunting extends well beyond harvest mortality. It alters how animals perceive risk, how they distribute themselves across landscapes, and how they allocate energy to survival and reproduction. These indirect effects accumulate into patterns of stress response, behavioural changes and space use, that can profoundly influence population resilience and management outcomes. Ultimately, this special issue contributes valuable pieces to a broader and complex puzzle describing the proximate and ultimate outcomes of hunting and its indirect effects. However, we believe that several important knowledge gaps remain. Here, we discuss only a few of them, with the aim of stimulating further research on this topic (Table 1). • How hunting interacts with natural predation (additive versus compensatory effects) • The impact of hunting-induced stress and behavioral shifts on the animal microbiome • Lack of long-term longitudinal studies (beyond 2–5 year funding cycles) • Taxonomic bias: over-reliance on temperate ungulates and large carnivores • How cultural motivations (e.g. subsistence versus trophy hunting) influence harvest patterns • How species use human-dominated areas as ‘human shields' or refuges Looking ahead, prospects for advancing our understanding of hunting impacts are increasingly promising, particularly given rapid technological developments (Samiappan et al. 2024, Okuley et al. 2025). Artificial intelligence applied to camera traps, drones, bioacoustics, and satellite-based animal tracking is already transforming our capacity to monitor wildlife at unprecedented spatial and temporal scales (Kitzes et al. 2025). These tools offer powerful opportunities to address long-standing questions, yet substantial gaps remain. To fully realise this potential, technological innovation must be paired with strategic investment that directs funding towards clearly defined research priorities rather than short-term or opportunistic applications. Below, we identify key research priorities that would particularly benefit from recent advances in technology, artificial intelligence, and wildlife monitoring (Table 1). One particularly promising avenue for future research would be to investigate how interactions between management systems – such as hunting practices and harvest quotas – and predatorsinfluence trophic cascades, especially in systems that are overwhelmingly occupied and driven by human hunters (Messerli et al. 2000, Mysterud et al. 2020). Although it is well established that natural predators and hunters impose different selection pressures (Proffitt et al. 2009, Ciuti et al. 2012b, Zeckhauser 2017), examining the effects of their varying combinations, and determining whether these effects are compensatory, additive, or interactive, would greatly enhance our understanding of the profound ecological and evolutionary consequences of hunting in a world with steadily increasing human-dominated landscapes. Hunting can substantially alter predator–prey interactions, yet these effects remain insufficiently resolved. By selectively removing prey or predators, modifying prey behaviour, or altering spatial and temporal activity patterns, hunting may reshape encounter rates, functional responses, and trophic feedback in ways that differ from those driven by natural predation, with consequences that can propagate across food webs. Replicated, long-term, landscape-scale experiments incorporating multi-trophic datasets remain rare. Without sustained measurements across plants, herbivores, predators, and ecosystem processes, studies risk overlooking delayed or spatially diffuse effects, as increasingly suggested by recent work on soil processes and avian communities (Mehlhoop et al. 2022, Amin et al. 2025). Another important direction for future research is to better disentangle physiological effects beyond those traditionally addressed in stress-focused studies. One emerging and largely unexplored aspect the animal exposed to human hunting pressure and fear have been to alter their behaviour et al. activity patterns et al. 2003), habitat selection et al. 2013), and feeding ecology and with likely consequences for and the associated with traits et al. how such changes affect foraging efficiency and life-history strategies a promising for advancing our knowledge of indirect hunting A further key issue consequences. Hunting is often in of artificial selection and the or of wildlife whereby certain and behavioural traits are by human hunters (Darimont et al. 2009, Ciuti et al. Although hunting has for the selective pressures imposed by and (e.g. tools to animals at or even to large areas and where animals are during the differ from those even a a contemporary hunting may be and artificial selection (Darimont et al. the of hunted populations is therefore and to evolutionary over and to whether hunting practices be to selection and more harvest of the research in this as well as many future advances in this on long-term longitudinal studies. strongly support the and of such study systems and against on the few long-term Although these systems have been long-term studies are funding is in – often to years – and research over multiple extremely evidence the and by long-term ecological studies et al. and therefore that is to funding and and to for long-term investment in wildlife monitoring is a critical need to disentangle lethal from non-lethal effects of to their importance, and only long-term monitoring can on such ecological long-term, studies consequences of direct mortality from or demographic indirect effects, a by et al. over-reliance on and of on systems and the the of studies on temperate ungulates and large carnivores in and North while taxa, and remain markedly the of current research the social of hunting do and its direct and indirect impacts on Milner et al. of hunting and wildlife vary widely across and contexts, as do motivations for hunting, ranging from subsistence to These differences can strongly influence which individuals are and how hunting pressure is across with potentially ecological consequences. research across the would be particularly valuable for understanding how social of hunting wildlife and conservation outcomes. The and consequences of hunting – such as hunting, drive or – are also particularly with to indirect impacts on species (Grignolio et al. and ecosystem et al. 2013). and species often exhibit behavioural and spatial responses to hunting to changes in habitat use, and movement patterns across landscapes. In the use of human-dominated areas as refuges or ‘human shields' by some with avoidance or displacement by others et al. 2013), may restructure and species interactions, yet across systems and hunting not operate in its effects interact with and yet studies or outcomes are et al. these be for a more and understanding of hunting in – are to and for their support during the of the papers in this special issue as well as during the of this all the for their contributions to the special – The no funding for this – The no of – – and – – and