Wildlife as a public trust

The public trust doctrine is a foundation for the Model. It is a concept that has evolved into common law from older Roman and English laws.^59,67 In English law, property was distinguished into two categories: 1) property the Crown could grant to private citizens and 2) property that the Crown held in trust for the general public. The latter properties were primarily coastal waters, navigable with the tides and offering access to important fisheries. American underpinnings of the public trust doctrine arose at the time of statehood from similar disputes around private and public rights over waterways and access to fisheries, which 19th-century American courts recognized were uniquely important to the public for navigation, commerce, and food.⁷ More than 100 yr later, the public trust doctrine provides the legal basis for private citizens who demand accountability of local, state, and federal government actions in disputes over land use that range from clean air and water to offshore oil drilling and climate change.⁵⁹

Reference to health in the public trust doctrine is primarily to public health, though paradigms that link animal, human, and ecosystem health (One Health) increasingly fall within public trust thinking.³⁵ For most wildlife populations, health is required for sustainability, so it follows that maintaining healthy wildlife falls under the public trust doctrine and is the responsibility of government wildlife management agencies (US state and federal; Canadian provincial) and the Crown (Canada).⁵² Fundamental to the doctrine is the concept that natural resources are universally valued by people and a public asset to be used and enjoyed by current and future generations. Under the public trust doctrine, natural resources (including but not limited to fish and wildlife) belong in common to all the people of the nation, and government agencies have legal responsibility for their care, including maintaining health.^59,64 At its core, the public trust doctrine is a democratic process, whereby the people elect representatives in government (the trustee) who enact, enforce and adapt wildlife management laws (e.g., protection laws, hunting and fishing laws and regulations, licenses, stamps) and wildlife or conservation policy (e.g., Endangered Species Act [ESA] of 1973,²² Migratory Bird Treaty Act of 1918,⁵⁰ Clean Air Act [CCA] of 196313 and Clean Water Act [CWA] of 1977¹⁴) on behalf of the people (the beneficiaries of the trust).⁶⁷ Thus, under the public trust doctrine, maintaining the health of wildlife populations is a social and legal obligation of the trustee.

What is wildlife health?

Defining health has been difficult and controversial in both human and veterinary medicine.³³ Historically, health has been defined as the absence of disease. However, this idea is antiquated and has been criticized on several levels: It fails to recognize that pathogens and parasites are ubiquitous in nature; that some level of disease may be normal and may serve a larger ecologic purpose; it does not address thresholds of disease that lead to illness or recovery; it overlooks the epidemiologic view that a population of animals can be healthy even while having diseased members; it is a reactive approach to disease that misses the opportunity to promote preventative health; and it is inconsistent with holistic thinking that sees health as a coping ability in the face of socioecologic interactions that are increasingly responsible for modern health threats (land use, global trade, introduced diseases, climate change, and invasive species).⁶⁶

The ambiguity of what wildlife health means and its historic focus on disease and pathogens has impeded the development of a shared concept of health across wildlife, domestic animals, and people. A modern definition for health should include resilience and sustainability of individuals and populations and a reorientation of management goals away from preservation of individual animals (except for critically endangered species) and toward sustaining populations, the complex ecosystems that support them, and their capacity to adapt.^2,34,73 Therefore, the concept of health is not purely a biologic or epidemiologic construct but is the output of a desired condition, namely, the ability of animals and populations to cope with change, particularly anthropogenic change. Core to this concept is that modern drivers of disease are more than pathogens and parasites themselves but include human-induced stressors, such as climate change, land use, pollution, invasive species, and wildlife trade.¹⁸ More than half a century before the present-day attempts to define wildlife health, Aldo Leopold (1944) wrote about health of the land as analogous to the functioning of an organism, with health being a condition of stability and self-renewal: “The land consists of soil, water, plants, and animals, but health is more than a sufficiency of these components. It is a state of vigorous self-renewal in each of them, and in all collectively.”⁴²

To understand how health supports, and is supported by, the Model, a definition of wildlife health that recognizes both the societal forces increasingly responsible for a departure from the desired condition one calls health and the ecologic resilience that helps protect wildlife from such deviations is required.^5,9,39 For these purposes a new definition of wildlife health is offered following Stephen⁶⁶ within the context of Leopold's three principles of health (stability, self-renewal, and ethos; 1944⁴²): Wildlife health is the interaction of biologic, social and environmental determinants that affect a wild animal population's ability to cope with change (stability), recover in the face of change (self-renewal), and meet societal goals (ethic). Stability and self-renewal are separate but complementary goals. Leopold (1944) equated stability with health of a diverse community.⁴² Health was associated with, and perhaps caused by, this diversity and complexity. More and more, species richness meant more and more complex relations between them, and this increase in species diversity correlates positively with increasing health. Leopold's self-renewal is analogous to resilience, defined by Walker et al. (2004) as “the capacity of a system to absorb disturbance and reorganize while undergoing change so as to still retain essentially the same function, structure, identity, and feedbacks.”⁷³ Resilience in an ecosystem requires redundancy of both function and response, whereby species fulfill more than one role in the ecosystem and individuals vary in their ability to deal with a threat, enabling some members of the population to survive change and the system to continue operating.³ Therefore, health is more than mere survival (not an end goal or target state), but rather a dynamic process. At the population health level, species build resilience and overcome vulnerabilities through high genetic diversity, and at the individual animal level, by changing behaviors in response to their environment throughout life.^20,60,75 Finally, healthy wildlife must be healthy in the eyes of the public and meet the goals and ethos (the guiding beliefs and ideals that characterize a group) society holds for their wildlife resources.⁵ This final part of the definition is especially critical when considering health in the context of the public trust doctrine that forms the heart of the Model. It is the healthy population, more than just the individual, which must meet societal goals. A definition of health that incorporates these three key elements will help realize the greatest impact on wildlife health and sustainability and stand the best chance of advancing policy.

Wildlife health and the Model

Even though the Model faces significant future challenges, it has endured as one example for sustainable natural resource stewardship. A main reason for the Model's enduring legacy is that it grants value to the public by clarifying ownership in, and management of, the nation's wildlife resource (a living asset) and, in so doing, empowers the public to help secure the resource for future generations.³⁵ Few attributes of a living asset could be considered more valuable than its health, both in terms of public perceptions and sustainability. Indeed, wildlife health, or the capacity of animal populations and ecosystems to exhibit stability and self-renewal, is dependent upon a public ethos for their management and preservation.⁵

The health of wildlife and the Model are uniquely integrated (Fig. 1), and the Model supports the health of wildlife (and, as a consequence, people) in diverse ways that extend well beyond the traditional values of disease surveillance and disease management. Likewise, the concept of health supports the Model. A modern definition of wildlife health can be used to show a wide application of the Model to protecting the health of both game and nongame species, as well as humans. Stability, self-renewal, and ethics all contribute to the unique interrelationships of wildlife health and the Model.

Figure 1.

The North American Model of Wildlife Conservation, a set of beliefs for the care of wildlife and wild places, is founded on the public trust doctrine. The Model's seven tenets protect wildlife health, and, in return, healthy wildlife give value back to the people as beneficiaries of the trust. The authors submit that the intergenerational model gives in perpetuity: when we take care of nature, nature takes care of us. Illustration credit to Laura Donohue

How the Model protects wildlife health

One of the most important contributions of the Model to the protection of wildlife health is stewardship of (e.g., surveillance of and informed actions that sustain) healthy animal populations (Fig. 1). Wildlife health research (science as a tool for wildlife policy) is essential for sound wildlife management, and it includes work in the fields of epidemiology, toxicology, parasitology, pathology, ecology, and climate sciences to name a few disciplines, all of which inform ecosystem-level processes. Although research can provide practical solutions, it is incumbent upon policy makers to enact these solutions; therefore, setting priorities for wildlife health research is critical to the future of the Model.^54,58 Although facts alone are not enough to guide important wildlife decisions and drive policy,⁵¹ science is a critical tool that provides much of the information that managers, administrators, and lawmakers need to debate policy. Given that there exist conflicting uses of wildlife (e.g., utilization vs preservation), it is essential that the best knowledge is used to develop strategies that satisfy the broadest public interest.⁶⁹ Financial support for trust management has historically come from consumptive interests (sales of hunting and fishing licenses, wildlife stamps, and taxes on ammunition and fishing tackle). Although the Model does not in itself provide funding and infrastructure for research, it does provide an underlying philosophy that government agencies use to allocate funding and guide how it is applied; see Model tenets such as “science is the proper tool for discharge of wildlife policy” (Table 1).⁵²

For endangered species, small populations are inordinately susceptible to health threats and management interventions can often mean the difference between survival and extinction.^18,49,44 A good example is the decline of the peregrine falcon (Falco peregrinus) as a result of organochlo- rine pesticide–induced eggshell thinning.²³ Although not endangered, the peregrine falcon had a limited number of breeding pairs prior to widespread use of dichlorodiphenyltrichloroethane (DDT), thus leaving them more susceptible to its effects.⁷² Research revealed a link between reproductive failure in the form of thin and weak eggshells and DDT contamination through bioaccumulation in the food chain in peregrine falcons, as well as many other fish-eating raptors, brown pelicans (Pelecanus occidentalis), and other species.^23,65 Science and policy decisions resulted in bans on the production and use of DDT and eventual recovery of the peregrine.⁸ In this case and others like it, the science-based approach of the Model facilitated health and management interventions that proved essential to preserve the wildlife resource and secure the public's investment in the future (wildlife resource of the public trust doctrine). Under the public trust doctrine, government agency intervention to save endangered species is mandated under the Endangered Species Act (ESA 1973),²² a landmark legislation made possible by the structure of the Model.²

Wildlife health monitoring, disease interventions, and health-related policy decisions are facilitated under the Model, but health threats to wildlife populations can also increase if one moves away from the Model. A good example is chronic wasting disease (CWD) and the effects of commercialization of wildlife. Efforts to deal with CWD as an emerging health threat to North American cervid populations has both benefited from tenets of the Model (science as a tool for wildlife policy: Table 1) and suffered from exceptions to the Model's application (failing to eliminate markets for game, and allocation of wildlife by law, by defining wildlife as agricultural animals and ignoring wildlife as an international resource, respectively). Knowledge about cervid health has benefited from intensive hunter harvest surveillance and culling, as have related monitoring and research efforts.³⁷ But the raising of captive cervids has exacerbated the emergence of CWD and represents a clear departure from the Model and public trust doctrine—while land can be privately owned, the wildlife living on the land must not be.⁵² With the raising of wild cervids in captive environments (game ranching) in North America, came a shift from public trust to private ownership, and management of captive wildlife by landowners complicates the control of a wildlife disease. A glaring weakness of the Model is that it is a set of principles rather than established law, so agencies of the government may at times ignore it, political and financial forces may compromise it, but sufficient social pressure can work through political and legal channels to reverse these exceptions.

How healthy wildlife gives value to the Model

There is perhaps no greater value of wildlife than the support of Earth's life systems (clean air, clean water, photosynthesis, carbon sequestration, and nutrient cycling), which healthy wild animals, plants, and intact ecosystems provide at minimal cost to people (Fig. 1).³⁹ If one agrees that the driving goal of the Model is to ensure that wildlife populations and the ecosystems they are a part of, are maintained for future generations (intergenerational equity), then humans will need to protect the processes that support wildlife (and human) health, even if one does not understand them fully.³⁵ To move science, to policy, to action, there is often a need for legislation to evolve (e.g., the Endangered Species Act) away from only saving individuals of a species and toward saving complex systems on which the populations depend.²

An overlooked aspect of wildlife is the nutrition and food security that healthy wild animals provide to people. Although the monetary value of wild harvests in North America are poorly understood, if humans were to lose the billions of pounds of wild animal protein from hunting and fishing, the replacement costs associated with domestic livestock production and modern agriculture would add considerable burdens to both the environment and the economy (Wild Harvest Initiative).⁴⁵ Indeed, in parts of the world where unsustainable practices have decimated wildlife populations, the loss of essential protein in the diet of the rural poor has significant health implications, including childhood anemia and cognitive deficits.³⁰ Indigenous peoples rely heavily on wild harvests of game, and an estimated 45 million Americans and Canadians annually engage in hunting and fishing for food.^68,74 When one considers that the amount of money recreational hunting and fishing pump into regional, local, and national economies exceeds the actual market value of the wild food, the larger economic value of harvesting wildlife becomes apparent.

People are connecting with nature in new ways that represent an evolution of the Model. One change is citizen science, and it has contributed significant new understanding of the natural world.^19,70,77 Given that the Model requires public approval and engagement, its value may be weakened by changing public perceptions of wildlife as a result of increased separation from nature, a lack of understanding of where food comes from, changing philosophies on animal rights, and a decline of hunting and fishing traditions. In this landscape, citizen science offers a unique opportunity for people to realize new value in wildlife and how natural systems are connected to their health.^4,19 Given the growing consensus that a broad alliance of people is necessary for resource conservation, one intimately connected with the health of a living asset, let us now explore controversies surrounding the Model and examine its relevance moving into the 21st century.

Controversy and the Model

Following the first written articulation of the Model by Geist in 1995, there has been mounting debate about its shortcomings.^12,61 Critiques of the Model focus on a handful of major challenges that can be viewed from two perspectives: 1) application of the Model to the wildlife resource (threats to wildlife stability and self-renewal) and 2) human perceptions of wildlife (threats to a public ethos for wildlife). In the first viewpoint, the application of the Model has suffered from confusion about public trust responsibilities resulting in a mosaic of state laws and policies, inadequate regulation of invasive species, the need for sustainable funding beyond a single user pay system, and a failure to incorporate indigenous peoples' knowledge and rights.³⁶ In the second viewpoint, the fitness of the Model is increasingly questioned as wildlife abundance brings conflict, private ownership competes with public ownership of wildlife, and a nonhunting public doubts the relevancy of the Model.⁷⁶ The latter is a consequence of the Model's historical focus on game animals at the expense of nongame wildlife that has favored hunters and anglers over other trust beneficiaries. Thorough reviews of these challenges can be found elsewhere.^12,51,61,69 Therefore, examining the shortcomings that most directly impact the connection between wildlife health and the Model is necessary: a focus on game animals, wildlife overabundance, and invasive species.

Focus on game animals at the expense of nongame animals: The Model's overt focus on hunting and fishing gives the perception that it lacks inclusion of other wildlife conservation interests.^6,29 A philosophy based predominately on harvest as a management tool does not adapt itself readily to more holistic ecosystem health approaches, and it is not very useful for the vast number of species (many of them threatened or endangered) that are not harvested. Although often used for sampling, hunting and fishing are not precise tools by themselves and are too often circumvented to make them a primary means of controlling most diseases and parasites. They are somewhat more useful for reducing health problems that are population associated, nutritional, and/or density dependent. Health threats have also arisen directly from hunting and angling, notably lead toxicity resulting from environmental contamination by lead-based ammunition and ingestion of lead fishing weights. This has hampered endangered species conservation programs, including the recovery of the common loon (Gavia immer) and bald eagle in the northeastern United States and the California condor (Gymnogyps californianus) in the West.^25,32,63 Concern regarding continued health risks to wildlife from lead has given rise to negative perceptions of hunters and anglers, in general, despite the many responsible individuals who are using and promoting nontoxic materials and the fact that many are simply unaware of the risks.

Wildlife overabundance: a new dilemma: Overwhelming land-use changes and decimation of predators (in part, an outcome of the Model) have created a new problem: wildlife overabundance. Many of the game animals prioritized under the Model have made remarkable recoveries. Today 30 million white-tailed deer (Odocoileus virginianus), 10 million beaver (Castor canadensis), 7 million wild turkey (Meleagris gallopavo), and 5 million Canada geese (Branta canadensis) are at levels wildlife managers consider overabundant or reaching densities that adversely affect other native species, ecosystems, or humans.²⁷ Most of these species are generalists or opportunists, primarily herbivores, but include carnivores and omnivores like the coyote (Canis latrans) and raccoon (Procyon lotor), which have benefited from large predator elimination, taken advantage of anthropogenic agricultural activities, or have adapted to urban landscapes. When wildlife grow so plentiful that conflict ensues, wild animals may be seen as a liability rather than a benefit, and some people increasingly see them as pests, vermin, or nuisances.^21,76

Leopold warned of the impending threats of too many deer on the landscape, and the ecologic toll can be significant with deer wreaking havoc on the forest understory, leading to widespread decline of migratory songbirds as a contemporary example.^10,16,40 However, the health implications to the deer, and to a variety of cohabitating wildlife species, are just as severe.³¹ Leopold recognized that the loss of top predators had an adverse effect on the health of the food web, affecting not only prey, but parasites and pathogens as well. The trophic cascade following the loss of top predators can lead to a disproportionate survival of unhealthy animals and a higher burden of disease in the system.⁵ Anthropogenic changes impacting the diversity of wildlife species and the structure of ecologic guilds may also affect public health—the overpopulation of deer and white-footed mice (Permomyscus leucopus) are largely responsible for the emergence of Lyme disease, the most common vectorborne epidemic in the United States.⁵⁵

Invasive species: Invasive alien species (IAS) are animals, plants, fungi, or microorganisms moved by humans to environments outside their original range, and being highly adaptable, often outcompete native animals and bring harm to ecosystems.¹¹ In the United States, invasive species are the second leading cause of floral and faunal extinctions, costing an estimated US$120 billion each year.¹⁶ Alarmingly, of the “100 World's Worst IAS” outlined in the Convention on Biological Diversity, one quarter of those listed are linked to diseases of wildlife.⁵⁷

The first federal court case affirming the public trust doctrine in the United States occurred in 1842. Leopold noted that by 1840, the beginnings of a decline in native plant and animal communities were evident, with the loss of iconic species such as the bison and passenger pigeon and the import of invasive sparrows, starlings, rodents, and pheasants.⁴² The Model arose at a time before significant global spread of species and, therefore, lacks any specific protections for native animal populations against harmful invasives. Furthermore, the Model's support for game animals for the purpose of harvesting has damaged the health of some native communities, including the movement of non-native game animals and fish that have degraded both landscapes and fisheries. Similarly, the movement of species from one area to another, whether for hunting, purposeful trans-location, or biologic control, is not addressed in the Model, and this has occasionally harmed both wildlife and human health.¹¹

Health and the future of the Model

A revival of the public trust doctrine has been attributed to the case law writings of Judge Joseph Sax and includes language that goes beyond consumptive uses of wildlife (primarily in the form of hunting and angling) to include individual rights to a healthy, diverse, and productive natural environment where clean air, clean water, and other natural resource entitlements, including the right to healthy wildlife, are defensible against a noncompliant government.^24,56,59 Thus, maintaining healthy wildlife has a legal as well as biologic, social, and moral basis.

Increasingly, one must recognize that the health of animals is intimately connected to one's own health (both physical and mental) and that of the environment.³⁹ The global pandemics arising from Ebola, human immunodeficiency virus, severe acute respiratory syndrome, and related corona-viruses threaten the foundation of species management, conservation, and health and challenge one to embrace a new understanding of the world.^18,26 The concept that health is shared among all living things has led to new viewpoints of health that reach across disciplines (e.g., One Health, conservation medicine, and Planetary Health), varying primarily in perspective and degree of anthropocentric thinking.⁴³

The authors agree with Nelson et al. (2011) in their critique of the Model when they argue that “the greatest value of the Model is that it highlights the need to confront a more basic question: What is conservation?”⁵¹ This perspective may help answer an equally urgent question facing society: Can humans appreciate how health (both one's own and that of cohabiting species) is central to a public trust, thereby bestowing upon us a responsibility for care of the earth? The Model has taken us a long way toward achieving healthy wildlife populations through a variety of means, including hunting and fishing. Notably, the public trust doctrine has garnered essential public interest that bestows value on natural resources, while giving citizens enforceable rights.^59,62 To keep the Model relevant, however, one should be open to new ideas of health that encompass far more than abundance of consumable fish and wildlife. Health must extend beyond a biologic state of individuals to include the ecosystems in which animals live, the processes that connect and sustain them, and, importantly, unite squarely behind a renewed societal contract, where human actions as a cohabiting species are held accountable.

Healthy wildlife as an ethic of modern society

In this perspective, it is reasoned that wildlife health supports the North American Model of Wildlife Conservation and, in turn, the Model protects the health of wild animals. Toward that end, wildlife health is defined as the interaction of biologic, social, and environmental determinants that affect a wild animal population's ability to cope with change (stability), recover in the face of change (self-renewal), and meet societal goals (ethic). The final tenet of the triad, meeting societal goals, is perhaps the most vital of the three because it serves to protect the first two. If one is to see the Model change to keep up with changing public attitudes and trends in natural resource use, the public must find real value in its wildlife resource. Health is perhaps one of the most easily understood values of a living system and serves to connect the realities of modern threats to wildlife with the need to protect its resilience through public education and deliberate guardianship.^5,21,34

In his land ethic, Leopold conveys the idea that individual respect for, and responsibility of, a community is part of an ethical sequence.⁴¹ The first part of this sequence is respect for the individual (the golden rule), the second is respect for society (democracy), and the final part is respect for the land organism, which he widened to encompass the soils, waters, plants, and animals. Leopold equated ethics with cooperation in a community and understood that “we can be ethical only in relation to something we can see, feel, understand, love, or otherwise have faith in.”⁴¹ Aldo Leopold never put down on paper a set of principles to define his land ethic. Rather, he believed that “nothing so important as an ethic is ever ‘written”’ and can only evolve “in the minds of a thinking community.”⁴¹ The thinking community, Leopold knew, would act with an ethical conscience if they believed “a thing is right when it tends to preserve the integrity, stability and beauty of the biotic community. It is wrong when it tends otherwise.”⁴¹ An ethic is a moral principle that affirms a form of conduct—in essence, it is the “trust” in the public trust that upholds the Model. Consequently, the Model provides the framework for a health ethic. Health brings integrity and stability and leads to the faith that Leopold hoped for; and so, the authors offer a simple addendum to Leopold’s land ethic: when we take care of nature, nature takes care of us.