U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2018–1128

Evaluation of Key Scientific Issues in the Report, 

“State of the Mountain Lion—A Call to End Trophy 

Hunting of America’s Lion”

Evaluation of Key Scientific Issues in the Report, 

“State of the Mountain Lion—A Call to End Trophy 

Hunting of America’s Lion” 

By James W. Cain III and Michael S. Mitchell

Open-File Report 2018-1128

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

RYAN K. ZINKE, Secretary

U.S. Geological Survey

James F. Reilly II, Director

U.S. Geological Survey, Reston, Virginia: 2018

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Suggested citation:

Cain, J.W., III, and Mitchell, M.S., 2018, Evaluation of key scientific issues in the report, “State of the 

mountain lion—A call to end trophy hunting of America’s lion”: U.S. Geological Survey Open-File Report 

2018-1128, 14 p., https://doi.org/10.3133/ofr20181128. 

ISSN 2331-1258 (online)
iii

Contents

Abstract ......................................................................................................................................................................1

Introduction................................................................................................................................................................. 2

Presumption That Hunting Limits Mountain Lion Populations.....................................................................................2

Selectively Cited and Interpreted Literature................................................................................................................3

Imprecise and Inadequate Demographic Measures ...................................................................................................4

Inadequate Estimate of Potential Lion Densities.........................................................................................................5

Management Implications...........................................................................................................................................9

Acknowledgments.....................................................................................................................................................10

References Cited......................................................................................................................................................10

Figure

Figure 1. USGS GAP range map and USGS Gap species distribution model used in the Humane Society of the 

United States (2017) mountain lion report to depict bighorn sheep availability as prey for mountain lions in the 

Western United States............................................................................................................................................... 8

Conversion Factors

International System of Units to U.S. customary units

Multiply By To obtain

Length

meter (m) 3.281 foot (ft)

kilometer (km) 0.6214 mile (mi)

Area

square kilometer (km2) 0.3861 square mile (mi2)

Abbreviations

HSUS Humane Society of the United States

MCP Minimum convex polygons

USGS U.S. Geological Survey
iv

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1 

Evaluation of Key Scientific Issues in the Report, “State of 

the Mountain Lion—A Call to End Trophy Hunting of 

America’s Lion” 

By James W. Cain III and Michael S. Mitchell

Abstract

In their recently published report, State of the Mountain Lion: A Call to End Trophy Hunting of 

America’s Lion, the Humane Society of the United States suggested that mountain lion (Puma concolor) 

hunting should be abolished in the United States. The report claims this recommendation is based on 

scientific arguments that demonstrate the overharvest of mountain lions throughout much of their 

current range in the United States. We reviewed the science presented by the Humane Society to support 

their call for the cessation of mountain lion hunting. Rather than provide a rigorous assessment of the 

peer-reviewed scientific literature and available data on mountain lion ecology, population dynamics 

and management, the report uses a fundamentally unscientific approach that starts with an a priori

assumption that hunting is detrimental to the long-term persistence of mountain lion populations, then 

attempts to use scientific arguments to support this value-based position. The report frequently ignores 

or selectively interprets relevant peer-reviewed literature, weakening the scientific credibility of the 

report. The report relies on imprecise and inadequate demographic measures, questionable data, and 

simplistic methodologies to derive dubious estimates of potential lion densities; it compares these 

estimates to various measures produced by State agencies (which themselves vary in reliability as 

estimates of abundance) to purportedly illustrate the detrimental effects of hunting. The approach used 

in the report to support the predetermined supposition that mountain lion populations are over-hunted 

fails to serve as a scientifically defensible foundation for management recommendations range-wide or 

at the State level.
2 

Introduction

The U.S. Geological Survey, Cooperative Fish and Wildlife Research Unit Program (CRUP) 

provides scientific guidance, technical training, and workforce development to program cooperators (PL 

86-686, Cooperative Research Units Act). Principal program cooperators are Department of the Interior 

agencies and state fish and wildlife agencies. A key role of the CRUP is to provide science support to 

program cooperators, which takes many forms including technical support on important fish and 

wildlife management issues. This includes meeting requests by cooperating agencies to peer review the 

scientific basis and merit of gray literature reports (reports not published in the peer-reviewed literature) 

that may have significance to their management programs. Consistent with the mission of the USGS, 

CRUP scientists provide objective and independent scientific reviews of such reports. Peer reviews 

focus on the strengths and weaknesses of referenced scientific information, interpretation, and 

assumptions, and make no assessments of policy or recommendations for natural resource management. 

This report represents such an effort, performed at the request of cooperating agencies.

The Humane Society of the United States (HSUS) recently published a report calling for the end 

of mountain lion (Puma concolor) hunting in the United States based on several scientific arguments 

(Humane Society of the United States, 2017). These arguments range from citing available literature on 

demography, ecology, and sociality of mountain lions, to the presentation of potential habitat and 

population sizes across 16 States where breeding populations exist. The U.S. Geological Survey 

(USGS) reviewed the science presented in the Humane Society of the United States (2017), focusing on 

subjects key to the conclusions of the report. 

Positions stated in the Humane Society of the United States (2017) are based on human values, 

in this case an opposition to “trophy hunting” in general and specifically the harvest of mountain lions. 

Although inherently subjective, these values are as legitimate as those of any other stakeholder in the 

effective conservation of wildlife in the United States. The report cites numerous polls to illustrate that 

these values are shared by a diversity of people. Indeed, these values may be increasingly prevalent in 

the United States as constituencies that have traditionally taken part in hunting and fishing decline 

(Manfredo and others, 2003; but see Butler and others, 2003 for an alternative finding).

All decisions in wildlife management are based on human values, including the value placed on 

science. Care must be taken, however, when scientific arguments are used to support recommendations 

based on other values. Science is easily misused on behalf of non-scientific agendas, becoming a 

seemingly objective but diversionary proxy for the subjective values behind the agendas (Mitchell and

others, 2018). The HSUS report falls short on four standards that would lend it scientific credibility: (1) 

an assumption that hunting limits mountain lion populations, (2) pertinent scientific literature either was 

ignored or selectively cited and interpreted, (3) imprecise and inadequate demographic measures were 

used to illustrate the detrimental effects of hunting, and (4) a scientifically inadequate estimate of 

potential lion densities was used to argue that hunting keeps densities of mountain lions below 

acceptable limits.

Presumption That Hunting Limits Mountain Lion Populations

It is human nature to seek evidence to support a value or belief (that is, confirmation bias; 

Kahneman, 2011). Humane Society of the United States (2017) begins with the supposition that hunting 

is limiting growth and threatening long-term persistence of mountain lion populations, then attempts to 

build a scientific case to support this belief; seeking evidence to argue a preconceived conclusion is 

inherently unscientific (Platt, 1964; Romesburg, 1981, 2009; Sells and others, 2018). The report cites 

but then ignores factors other than hunting that could influence lion populations across their range (that 

is, habitat loss and fragmentation, poaching, disease, starvation, inbreeding, intraspecific strife, 
3 

poisoning, and climate change; Humane Society of the United States, 2017, p. 36–37). The scientific 

remedy for confirmation bias is to evaluate the evidence for alternative explanatory causes for observed 

phenomena (Sells and others, 2018). Without an objective evaluation of all factors potentially 

influencing mountain lion populations, it cannot be concluded that hunting is the dominant limiting 

factor, as the report claims. The evidence needed to objectively evaluate factors influencing 

demography of mountain lions is rare and sparse across the full range of mountain lion populations in 

the United States. An analysis of all available information almost certainly would have shown much 

more ambiguous and uncertain patterns than the report currently presents. 

Selectively Cited and Interpreted Literature

The report cites numerous peer-reviewed publications to support its recommendation against 

hunting of mountain lions. In building this case, the report frequently fails to reference relevant 

publications offering contrary conclusions, or offers selective interpretations, thereby failing to 

thoroughly assess all pertinent results, assumptions, and critical caveats detailed in the original peerreviewed papers. Selective use of peer-reviewed scientific literature is misinformative, particularly for 

readers unfamiliar with published research, which diminishes the credibility of the report. 

For example, the report repeatedly claims that trophy hunting is the most important threat to the 

persistence of mountain lion populations. This claim generally is not supported by the peer-reviewed 

literature. Research has shown that hunting mortality is additive for mountain lion populations and thus 

has the potential to cause declines where hunting is high and sustained, but these populations are highly 

resilient and can recover quickly (Lindzey and others, 1992; Logan and Sweanor, 2001; Stoner and 

others, 2006; Robinson and others, 2014). Therefore, even heavy hunting does not inevitably cause 

irretrievable declines in mountain lion populations. Importantly, there is broad consensus among 

wildlife ecologists that habitat loss, degradation, and fragmentation are the primary threats to the 

survival of most wildlife species in the United States (Wilcove and others, 1998); mountain lions are no 

exception. Habitat loss and habitat fragmentation, including the effects of habitat alterations on prey 

species, are considered the most important threats to persistence of mountain lions (Logan and Sweanor, 

2001; Pierce and Bleich, 2003, Cougar Management Guidelines Working Group, 2005; Anderson and 

others, 2009; Negri and Quigley, 2009).

Humane Society of the United States (2017) also states unequivocally that ungulate populations 

are food limited and that predator removal has little effect on the productivity of ungulate populations. 

Whether or not an ungulate population is nutritionally limited or whether predation may be a 

compensatory or additive source of mortality depends on population size relative to carrying capacity 

(Ballard and others, 2001; Bowyer and others, 2014; Monteith and others, 2014; Bergman and others, 

2015). When populations are at or above carrying capacity, animals tend to be in poor nutritional 

condition, produce small offspring, and are strongly susceptible to predation or mortality due to effects 

of severe weather or disease; predation on these populations often is compensatory (Bergman and 

others, 2015). Controlling predators when ungulate populations are near carrying capacity typically has 

little influence on population growth (Ballard and others, 2001; Bergman and others, 2015). However, 

ungulate populations below carrying capacity generally are composed of individuals in good nutritional 

condition that produce more offspring that likely have higher survival rates than populations near or 

above carrying capacity (Bowyer and others, 2014, Monteith and others, 2014, Bergman and others, 

2015); predation on these populations often is additive. The review on mule deer (Odocoileus hemionus) 

and black-tailed deer (O. h. columbianus) by Forrester and Wittmer (2013) and other publications cited 

in Humane Society of the United States (2017) (Watkins and others, 2001; Pojar and Bowden, 2004; 

Bishop and others, 2009) to support the blanket claim of food limitation in ungulates, suggests that 
4 

many of these studies were of populations at or near carrying capacity. Low abundance commonly 

typifies ungulate populations of serious management concern. When population abundance is low and 

well below carrying capacity, moderate predation rates can hamper recovery even if other limiting 

factors are alleviated, thus precluding recovery of the population (Ballard and others, 2001). For 

example, predation by mountain lions was reported to contribute to declines of small populations of 

desert bighorn sheep (Ovis canadensis nelsoni and O.c. mexicana; Wehausen, 1996; Ernest and others, 

2002) or to hamper recovery efforts (Hayes and others, 2000; Kamler and others, 2002; Rominger and 

others, 2004). All these peer-reviewed papers describe results that are contrary to the claim in Humane 

Society of the United States (2017) that mountain lions have no effect on bighorn sheep populations, but 

none of these publications were cited in the report.

In another example, citing Collins and Kays (2011), Coltman and others (2003), and Monteith 

and others (2013) the HSUS report claims that hunter harvest has led to evolutionary changes in 

behavior and morphology, compromising the ability of ungulates to adapt to changing conditions. 

Collins and Kays (2011) reviewed literature about the cause of mortalities for medium- and large-size 

mammals. They concluded that humans cause most of the mortality (that is, 51.8 percent versus 48.5

percent due to natural causes), but they do not, as implied in the HSUS report, provide any data 

demonstrating evolutionary changes due to human-caused mortalities in general or hunting. Coltman 

and others (2003) and Monteith and others (2013), provide data more directly related to potential 

changes in morphology of ungulates in response to human harvest. However, the bighorn sheep 

population studied by Coltman and others (2003) was subjected to unlimited harvest of legal rams, 

unlike the more conservative harvest limits imposed by management agencies for most populations 

across the species’ range (Heffelfinger, 2018). Additionally, the Coltman and others (2003) study did 

not account for the effects of population density, nutrition, maternal effects, or shifting age distributions 

due to harvest on changes in average horn size of the population. Some of these factors have a stronger 

effect on ungulate morphological characteristics than purported genetic changes due to selective human 

harvest (Coltman, 2008; Monteith and others, 2013; Traill and others, 2014; Douhard and others, 2017; 

Heffelfinger, 2018). Therefore, Humane Society of the United States (2017) selectively cites literature 

to support its premise while avoiding mention of the ongoing and rigorous debate among ecologists 

about the evidence for evolutionary consequences of trophy hunting (Coltman and others, 2003; 

Darimont and others, 2009; Traill and others, 2014; Heffelfinger, 2018).

Imprecise and Inadequate Demographic Measures

Identifying a measurable demographic parameter for understanding and managing large 

carnivores is notoriously difficult because they occur at low densities, range widely, and are highly 

elusive. Scientific careers have been built on the challenges of understanding demography of animals 

much easier to study. This challenge becomes much greater when imprecise concepts and definitions are 

used. Terms such as population size, trend, census, abundance, estimates, habitat, density, home range, 

and mortality have precise scientific definitions but are used loosely, inconsistently, and sometimes 

interchangeably throughout Humane Society of the United States (2017). For example, figures and 

discussion of mountain lion mortality in appendix B are misleading. The text reports trophy hunting 

mortality (presumably including animals killed through legal harvest) as a percentage of total humancaused mortality (presumably including vehicle collisions, depredation removals, poaching, and other 

factors), then inappropriately draws conclusions that trophy hunting mortality parallels human-caused 

mortality and total overall mortality (presumably including all forms of mortality such as starvation, 

intraspecific killings, and other mortality sources). Associated figures suggest a comparison between 

trophy hunting mortality and total mortality (presumably the same as overall mortality). Overall or total 
5 

mortality do not equate to total human-caused mortality and the report offers no evidence of having 

obtained or generated estimates of total or overall mortality. This imprecise terminology can lead to 

subjective, divergent inferences about the effects of hunting on mountain lion populations. Comparing 

hunting mortality to all human-caused mortality is not informative if, as appears to be the case, most 

human-caused mortality is produced by hunting. Conversely, comparing hunting mortality to overall 

mortality can produce information highly useful for managing harvested species (that is, whether 

hunting mortality is compensatory or additive; Robinson and others, 2014). Because of the 

inconsistencies in terminology, the HSUS report presents evidence only for the former comparison but 

appears to reach conclusions as if based on the latter, selectively leading the reader to an erroneous 

inference.

The most fundamental demographic measure for understanding and managing populations 

arguably is abundance. Estimates of abundance can represent a key bottom line that is central to most 

management questions—how many animals are there and how has that changed over time? In the 

absence of such information, it is difficult to understand population dynamics and how they are 

influenced by a variety of factors, including hunting. Humane Society of the United States (2017) makes 

the case that such understanding is an important component of harvest management, finding fault with 

state agencies for making harvest decisions based on less reliable data such as harvest returns (although 

offering no financially or logistically feasible solutions to the problem). However, Humane Society of 

the United States (2017) makes the same error for which it criticizes the state wildlife management 

agencies: without knowing annual abundance it uses annual harvest data to support the claim that 

hunting has an unacceptably detrimental effect on populations of mountain lions. Without credible 

evidence that hunting is associated with declines in abundance, it is impossible to make the argument 

that hunting or any other factor is responsible for declines in population, the central argument put forth 

in the report. Even if, for example, hunting mortality comprises most of the mortality, unless it is known 

whether total mortality is sufficient to cause declines in abundance, the conclusion that hunting 

mortality has deleterious demographic consequences is logically indefensible. Importantly, even if 

hunting mortality is associated with a decline in abundance its meaning must be interpreted according to 

management objectives that states seek to achieve through harvest. If the objective is to reduce the size 

of the mountain lion population through regulated hunting, then hunting mortality should, by design, be 

associated with a decline in abundance. 

Inadequate Estimate of Potential Lion Densities

In an attempt to build further support for the position that mountain lions are overharvested 

Humane Society of the United States (2017) constructed a simple habitat-based model to estimate 

potential mountain lion abundance. These estimates of potential lion abundance were compared to a 

variety of estimates used by State wildlife management agencies, and the report concluded that almost 

all States are overharvesting mountain lions. The report describes abundance estimates as “most suitable 

density” (p. 6), “potential optimal abundance” (p. 25), and “healthy densities” (p. 6). However, these 

terms have no precise, operational definitions in the fields of population and wildlife ecology and the 

report does not offer any definitions. Without an established operational definition, the biological 

meaning of each those terms is not clear, making their interpretation subjective based on the reader’s 

personal values and knowledge of population ecology. The use of vague terms obscures the 

questionable assumptions and methodological approaches behind the estimation of potential lion 

abundance in the report. 
6 

Comprehensive habitat modeling when coupled with rigorous estimates of abundance and other 

demographic parameters (for example, productivity and recruitment) can provide meaningful 

information for managing wildlife (Mitchell and Hebblewhite, 2012). A credible population or habitat 

modeling effort includes a rigorous assessment of the accuracy of the underlying data, assumptions 

made when using the data, and the assumptions inherent to the models used. Model prediction results

are then tested (that is, evaluating how well model predictions fit independent data) or validated (for 

example, cross validation). Furthermore, when presenting a point estimate of abundance (or any other 

estimated parameter of interest), an estimate of precision or uncertainty should accompany the estimate. 

The modeling presented in Humane Society of the United States (2017) does not meet any of these 

criteria, and that failure compromises the validity of the resulting abundance estimates.

Overall, the data and modeling approach used to estimate potential mountain lion density in the 

report are problematic. There are critical issues with the nature of prey data selected, the use of 

relatively small female home range sizes for delineating habitat classifications, vague classifications of 

habitat quality, use of a fixed lion density estimate across the western United States, questionable 

assumptions in the modeling process, and the use of the derived abundance estimates without an 

assessment (either formal or informal) of associated uncertainty.

Although mountain lions occupy a wide range of environments, prey abundance, vegetation, and 

topographic features that contribute to hunting success, and human disturbance commonly are 

considered important habitat components wherever mountain lions occur (Seidensticker and others, 

1973; Logan and Irwin, 1985; Lindzey, 1987; Laundré and Hernández, 2003; Robinson and others, 

2015). Informed selection of available geospatial data for habitat modeling is primarily based on the 

questions or hypotheses of interest that the modeling is intended to address. The selection criterion for 

data used to model habitat and prey characteristics in Humane Society of the United States (2017) was 

based on coverages that were consistently available across the western United States, rather than the 

data needed to accurately capture the broad variation in critically important habitat components across 

the diversity of ecoregions occupied by mountain lions. The model used for the HSUS report attempted 

to account for the effects of topographic variation, prey, and human disturbance; vegetation cover data 

and their potentially important contribution to stalking cover were omitted from the modeling. The 

limits imposed by data availability and completeness on comprehensively modeling important habitat 

characteristics across broad geographic extents hampers all habitat modeling (Barry and Elith, 2006). 

Any habitat modeling effort, therefore, makes two critical assumptions: (1) available data are sufficient 

to model key habitat characteristics, and (2) the inability to model habitat characteristics for which no 

data are available does not biologically invalidate model predictions. A scientifically credible habitat 

model requires a forthright discussion of these assumptions, as well as a discussion of the potential for 

bias in model predictions if any assumptions are violated. 

Prey data used in the model were obtained from the U.S. Geological Survey National Gap 

Analysis Program (2011a, b) for bighorn sheep (O. canadensis) and elk (Cervus elaphus canadensis); 

mule deer and black-tailed deer data were obtained from Utah State University (2005). These data 

represent estimated distributions or maps of areas where conditions have the potential to be occupied by 

these prey species (that is, potential habitat). Distribution models of potential habitat for mule deer, elk, 

and bighorn sheep are poor substitutes for actual data on prey abundance and availability. The 

distribution model data do not depict the biologically meaningful spatial variation in abundance of prey 

species, nor do they always represent the actual distribution of extant populations of prey across their 

range. Density of prey throughout the distributional ranges was assumed to be constant, ignoring spatial 

variation in density of ungulate populations. For example, mule deer distribution data clearly designate 

substantial areas as “limited range” that are occupied only occasionally or by small populations (Utah 

State University, 2005). Similarly, the modeling referenced in Humane Society of the United States 
7 

(2017) equates low density mule deer populations in the Desert Southwest and high density populations 

in Montana and Wyoming, leading readers to assume density of mule deer is constant across their range, 

thus serving as a spatially consistent source of prey for mountain lions. 

Critically important, the distribution ranges do not necessarily reflect the actual distributions of 

prey populations. For example, the bighorn sheep data used in the modeling included broad areas where 

no bighorn sheep populations currently exist (Western Association of Fish and Wildlife Agencies 2016; 

fig. 1). The data produced by USGS and Utah State University are not themselves problematic, but the 

assumption that the data provide a reliable depiction of the prey resources needed to support a lion 

population is. Accounting for the wide spatial variation in prey abundance within the boundaries of the 

distribution ranges would provide more meaningful information on the spatial variation in mountain lion 

densities that certainly exist on the landscape (for example, Carbone and Gittleman, 2002; Karanth and 

others, 2004).

Additional issues with two assumptions made in the geospatial modeling warrant discussion. 

Briefly, the basic modeling approach assigned a weighted sum to each pixel based on values for prey, 

terrain ruggedness, and human footprint. The pixels were partitioned along a habitat quality gradient 

ranging from non-habitat to optimal, and considered only the highest three habitat classes (average, 

good, optimal) to be capable of supporting mountain lions (Humane Society of the United States, 2017). 

The estimates of habitat areas for each state (that is, the total area from which the abundance estimates 

were derived) were based on a moving window approach in which each focal cell was assigned a habitat 

value based on the majority habitat value of the pixels within the moving window. A primary flaw was 

the assumption that a single value for mountain lion density would be accurate for estimating abundance 

across the western United States. Empirical estimates of mountain lion density vary widely across the 

United States (0.3–2.2 adults/100 km2

), mostly due to differences in prey abundance and habitat 

conditions (Seidensticker and others, 1973; Logan and others, 1986; Anderson and others, 1992; Ross 

and Jalkotzy, 1992; Beier and Barrett, 1993; Lindzey and others 1994; Logan and others, 1996; 

Spreadbury and others, 1996; Pittman and others, 2000; Logan and Sweanor, 2001). Because different 

ecoregions have inherently different capacities to support mountain lion populations, the use of a single 

density value both over- and under-estimates potential mountain lion abundance in different parts of 

their range. Moreover, the assumption that a 5-km moving window represents the typical home range 

radius (about 78.5 km2

) for an adult female mountain lion does not withstand scrutiny. Although female 

home ranges (estimated as 90–100 percent kernel density functions or minimum convex polygons 

[MCP]; Worton, 1989) less than or equal to 78.5 km2 are reported in the peer-reviewed literature (Logan 

and others, 1986; Hopkins, 1989; Spreadbury and others, 1996; Logan and Sweanor, 2001), much larger 

home ranges have been reported in many areas, commonly in excess of 140–250 km2 (for example, 

Hemker and others, 1984; Neal and others, 1987; Pence and others, 1987; Anderson and others, 1992; 

Ross and Jalkotzy, 1992; Beier and Barrett, 1993; Pierce and others, 1999; Pittman and others, 2000; 

Dickson and Beier, 2002; Grigione and others, 2002). If a larger home range size was used for the 

moving window, many areas ultimately classified as average habitat would have been more likely to 

have been classified into one of the lower habitat classes, thus resulting in a lower abundance estimate. 

Home range size in mountain lions is strongly inversely related to prey abundance or density (Grigione 

and others, 2002). Therefore, potential errors generated due to fixed, small home ranges and fixed lion 

density would be exacerbated in areas characterized by low prey abundance, lower lion densities, and 

larger mean home range sizes. Finally, any estimate of density, abundance, or any other estimated 

parameter, almost without exception, needs to be accompanied by an estimate of precision or 

uncertainty. 
8 

Figure 1. USGS GAP range map and USGS Gap species distribution model used in the Humane Society of the 

United States (2017) mountain lion report to depict bighorn sheep availability as prey for mountain lions in the 

Western United States. The actual distribution of extant populations of bighorn sheep (Western Association of Fish 

and Wildlife Agencies. 2016) is superimposed on the GAP range map and distribution model.
9

Potential habitat or presence of critically important habitat components (for example, prey, 

stalking cover) can be modeled if accurate data upon which to build the model are available. Habitat 

quality (that is, the extent to which habitat characteristics contribute to fitness; Mitchell and 

Hebblewhite, 2012), however, is best determined based on demographic rates of the species of interest 

(Van Horne, 1983; Johnson, 2007). Instead, Humane Society of the United States (2017) identifies 

potential mountain lion habitat using predetermined categories that are based on a vague 

conceptualization of the number of lion territories (for example, “Good—many lions can occupy as 

home range, can support a breeding population;” Humane Society of the United States, 2017, p. 25) that 

could exist in a given area. The categorical classifications of mountain lion habitat quality are based on 

the summation of habitat characteristic scores used in the geospatial habitat model and are based on 

neither demographic attributes nor peer-reviewed research. To be most informative for estimating 

statewide abundances, habitat modeling is best coupled with estimates of mountain lion abundance or 

demographic rates (for example, survival) derived from field studies on lion populations spanning the 

range in habitat conditions depicted in the geospatial model.

Authors of Humane Society of the United States (2017) indicated that population estimates used 

by state agencies do not provide information appropriate to making management decisions. In reaching 

conclusions about over-harvest, however, the state estimates presented in the report (modified to 

represent adults only based on age ratio data from a single population in New Mexico, Logan and 

Sweanor, 2001) were quantitatively compared to the estimated potential population sizes derived from 

the models presented in the report. This reasoning is difficult to understand. If the density and 

abundance estimates used by state agencies for management of mountain lion populations are inherently 

flawed, then those data probably do not serve as a good benchmark for comparison to estimates derived 

from modeling used for the report. When combined, the uncertainties in the variety of abundance 

estimates used by states, the assumptions made when modifying those estimates to represent only adult 

animals, and the unassessed uncertainties of estimating potential abundance based on their simplistic 

habitat model, comparisons of state estimates and those produced as part of Humane Society of the 

United States (2017) does not support the conclusion that mountain lions are generally overharvested 

and should be protected.

Management Implications

Humane Society of the United States (2017) argues against hunting of mountain lions based on 

human values, while attempting to demonstrate scientific support for those values. The science used to 

support the foregone conclusion that mountain lions generally are over-hunted is of insufficient logical 

and methodological rigor to be credible. Importantly, the unsubstantiated contentions distract from two

important points made in the report that are difficult for anybody to argue: (1) parts of American society 

are decreasingly tolerant of hunting mountain lions and (2) harvest decisions made by state agencies 

would benefit from more rigorous measures of population estimation. Few managers would disagree 

with either of those points. The question then becomes what are the realistic approaches management 

agencies can take to address them. Failing to adapt to societal changes can lead to loss of management 

authority by state agencies (for example, ballot initiatives that led to the ban on mountain lion hunting in 

California; Bleich and Pierce, 2005), but the reasonable means of adaptation may be unclear. 

Management of mountain lion hunting would be more transparent and quantitatively defensible if it 

were based on rigorous population estimates, but reasonable means of support and methodological 

approaches for doing such monitoring are yet to be discovered or widely adopted. Quasi-scientific 

arguments based on preordained, value-based conclusions are not likely to provide clarity to either of 

these issues.
10

Acknowledgments

Reviews and insightful comments by V.C. Bleich, P.R. Krausman, H.S. Robinson, and J.K. 

Young improved an early draft of this manuscript.

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Cain and others—valuation of Key Scientific Issues in the Report, “State of the Mountain Lion”—A Call to End Trophy Hunting of America’s Lion—Open-File Report 2018–1128

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