Abstract

Bobcat Lynx rufus populations are thought to be increasing in North America; however, little information exists on their current population status. In the United States, management and monitoring of bobcat populations is the responsibility of state wildlife management agencies. We surveyed state wildlife management agencies in each of the 48 contiguous states regarding the current population status, distribution, and monitoring protocols of bobcats within each respective jurisdiction. We also surveyed the governments of Mexico and Canada regarding bobcat population status within their jurisdictions. We received responses from 47 U.S. states, Mexico, and 7 Canadian provinces. Responses indicate that bobcats occur in each of the contiguous states except for Delaware. Populations were reported to be stable or increasing in 40 states, with 6 states unable to report population trends and only 1 state (Florida) reporting decreases in bobcat populations. Of the 47 states in which bobcats occur, 41 employ some form of population monitoring. Population density estimates were available for 2,011,518 km2 (33.6%) of the estimated bobcat range in the United States, with population estimates between 1,419,333 and 2,638,738 individuals for this portion of their range and an estimated 2,352,276 to 3,571,681 individuals for the entire United States. These results indicate that bobcat populations have increased throughout the majority of their range in North America since the late 1990s and that populations within the United States are much higher than previously suggested.

Introduction

Bobcats Lynx rufus are one of the most widely spread and adaptable carnivores in North America (Anderson 1987). Bobcats serve as a top predator in many ecosystems (Conner et al. 2001) and can have significant effects on ecosystem function. For example, bobcats have been identified as a significant source of predation, in specific systems, for white-tailed deer Odocoileus virginianus (Nelms et al. 2001), cotton rats Sigmodon hispidus (Schnell 1968), and pronghorn Antilocapra americana (Beale and Smith 1973). Thus, in many situations, proper management of bobcat populations may be an important component of managing for ecosystem function and biodiversity.

In the United States, management of bobcat populations is the responsibility of state wildlife management agencies. However, management of bobcats, as with many other carnivores, can be difficult due to their elusive nature and the lack of information on demographic rates. Changes in bobcat management in response to population trends are common (Rolley et al. 2001); however, most population assessments or studies of bobcat range have been limited in geographic scope (e.g., Woolf et al. 2002). It is generally assumed by managers that a harvest rate of 20% is sustainable (Knick 1990), but that variability in environmental factors may confound this (Anderson and Lovallo 2003). The vast geographic range of bobcats in North America highlights the need for large-scale population assessments. Bluett et al. (2001) reported that state agencies considered distribution and relative abundance to be among the most important research topics for bobcats.

Woolf and Hubert (1998) provided the most recent assessment of bobcat population distribution and management in North America, with the most recent range-wide population assessment occurring in 1981 (USFS 1981). However a more contemporary assessment is needed because human populations and development have increased greatly during the past decades. Although numerous regional or local studies have suggested that bobcat populations are increasing (e.g., Woolf et al. 2000), no empirical evidence of range-wide increases in population abundance exists. Our objective was to document monitoring efforts, spatial distribution, and population trends of bobcats in North America.

Methods

Agency surveys

We contacted wildlife management agencies from all of the 48 contiguous states of the United States, 7 Canadian provinces (British Columbia, Manitoba, New Brunswick, Nova Scotia, Ontario, Quebec, Saskatchewan), and the country of Mexico in 2008. Each jurisdiction was asked to report: 1) what methods are employed to monitor bobcat status, 2) population estimates and average densities (if available), 3) the area (reported here in km2) of suitable bobcat habitat within the jurisdiction, and 4) post-1981 population trends. Monitoring methods were classified as public sightings, harvest analysis, hunter surveys, population models, scent or sign stations, snow track surveys, incidental harvest, vehicle collisions analysis, or other. We primarily present information from U.S. states to facilitate comparison with previous studies and population estimates (USFWS 1982; Woolf and Hubert 1998) and for brevity.

Data analysis

We compared the proportion of states reporting increasing or stable populations between 1996 and 2008 (Woolf and Hubert 1998) using chi-square tests. We only included states that reported population trends in this analysis. States that reported populations as “stable/increasing” were assigned a status of “stable” for this analysis. We estimated minimum population abundance and total suitable habitat as the sum of population or habitat estimates across all jurisdictions. Because not all states reported estimated population abundance (n  =  26) or area of suitable habitat (n  =  5), we considered these minimum estimates to be very conservative. To estimate total population abundance across the contiguous United States, we calculated average bobcat density for those states reporting both population and area of habitat estimates and then multiplied this average by the geographic range estimates for all states that reported range estimates but no population estimates (n  =  17) and added this value to the minimum count. This method provided a general estimate of population abundance across the entire United States that facilitates comparison with historic estimates that used similar methods (USFWS 1982).

Results

We received responses from 47 of the 48 states, 7 Canadian provinces, and Mexico. Responses indicated total area of suitable bobcat habitat of 8,708,888 km2, with 71% (6,186,819 km2) in the United States, 20% in Mexico (1,702,545 km2), and 9% in Canada (819,524 km2). Twenty-eight (50.9%) of the jurisdictions reported population estimates or densities (Table 1). Of the 48 jurisdictions that reported population trends, 31 (64.6%) reported increasing populations while 15 (31.3%) reported stable populations, and 1 reported fluctuating populations. Only one jurisdiction, Florida, reported decreasing bobcat populations (Figure 1). The minimum population estimate in the United States was between 1,418,333 and 2,637,738 individuals, representing 68.4% of the total estimated bobcat range in the United States (Table 1). Using average density, the total population abundance in the United States was estimated to be between 2,352,276 and 3,571,681 individuals. A significantly higher (χ2  =  5.64, P  =  0.018, df  =  1) proportion of states reported increasing populations in 2008 than in 1996.

Figure 1

Bobcat population trends in the contiguous United States, 2004.

Figure 1

Bobcat population trends in the contiguous United States, 2004.

Table 1

Bobcat monitoring methods (Monitoring), population estimates (N), range extent (Habitat, in km2), and population status (Status; 1981–present) for selected jurisdictions in North America. NR indicates data were not reported by jurisdiction. Monitoring methods were public sightings (PS), harvest analysis (HA), hunter surveys (HS), population models (PM), scent or sign stations (SS), snow track surveys (TS), incidental harvest (IH), vehicle collisions analysis (VC), or other (OT).

Bobcat monitoring methods (Monitoring), population estimates (N), range extent (Habitat, in km2), and population status (Status; 1981–present) for selected jurisdictions in North America. NR indicates data were not reported by jurisdiction. Monitoring methods were public sightings (PS), harvest analysis (HA), hunter surveys (HS), population models (PM), scent or sign stations (SS), snow track surveys (TS), incidental harvest (IH), vehicle collisions analysis (VC), or other (OT).
Bobcat monitoring methods (Monitoring), population estimates (N), range extent (Habitat, in km2), and population status (Status; 1981–present) for selected jurisdictions in North America. NR indicates data were not reported by jurisdiction. Monitoring methods were public sightings (PS), harvest analysis (HA), hunter surveys (HS), population models (PM), scent or sign stations (SS), snow track surveys (TS), incidental harvest (IH), vehicle collisions analysis (VC), or other (OT).

Of the 55 jurisdictions surveyed, 45 (81.2%) reported methods used to monitor bobcat populations, 25 (55.6%) of which used > 1 method. Harvest data analysis and hunter surveys were the most commonly used methods (Table 2). No jurisdiction used > 5 methods to monitor bobcats. Only one jurisdiction (Oregon) reported having bobcat populations but no monitoring method.

Table 2

Methods used to monitor bobcat populations in the lower 48 states and 7 Canadian provinces in 2008 (45 jurisdictions reporting). Twenty-five jurisdictions used > 1 method.

Methods used to monitor bobcat populations in the lower 48 states and 7 Canadian provinces in 2008 (45 jurisdictions reporting). Twenty-five jurisdictions used > 1 method.
Methods used to monitor bobcat populations in the lower 48 states and 7 Canadian provinces in 2008 (45 jurisdictions reporting). Twenty-five jurisdictions used > 1 method.

Discussion

Bobcats are highly adaptable carnivores and are the most abundant of North America wild felids (Cowan 1971; Anderson and Lovallo 2003). Their ecological role and economic value as furbearers are the primary motivations behind research and management of bobcats (Woolf and Nielsen 2001). Woolf and Hubert (1998) reported that less than half of the states in the contiguous United States (n  =  20) had increasing bobcat populations as of 1996; however, we found that 32 states now report increasing populations (Table 1). All other states that reported bobcat population trends, with the exception of Florida, reported at least stable populations.

Although the magnitude of population increase likely varies considerably among jurisdictions, the general trend supports the hypothesis that bobcat populations are expanding across much of their geographic range. The reason for declining populations in Florida is unknown, although extensive human development may be partly responsible. Given the stability of bobcat populations elsewhere in the United States, the decreasing population in Florida does not pose any immediate threat to the large-scale persistence of bobcat populations in the United States. However, research into the vital rates and demographic patterns of the Florida bobcat population could provide useful information to wildlife managers if populations elsewhere begin declining.

Minimum population estimates provided by jurisdictions indicated that the United States' bobcat population is > 1.4 million. This estimate is likely a substantial underestimation of total population abundance, because it only represented population estimates for approximately 68% of the reported bobcat range. In 1981 similar methods were used to estimate bobcat populations; at that time it was estimated there were 725,000–1,017,000 bobcats in the United States (USFWS 1982). Using these methods, our data indicate that current bobcat population abundance in the entire United States is 2,352,276–3,571,681. This growth is likely the result of many factors including changing agricultural and land-use practices, range expansion, and habitat improvement programs such as the Conservation Reserve Program (FSA 1985, 16 U.S.C. 3831). In addition, advances in wildlife management and monitoring have allowed states to greatly improve wildlife management programs in recent decades, particularly furbearer management. As recently as 1971, 40 of the 48 contiguous United States had no protection or formal management of bobcats (Faulkner 1971). In New York, for example, bobcats were designated as an unprotected species and take was unregulated through 1976, only 5 y prior to the 1981 population estimate (USFWS 1982). After 1976, bobcats were afforded legal status as a furbearer species to be conserved, and harvest regulations were developed and implemented. Similar shifts in management paradigms have occurred in many jurisdictions; these have clearly benefited bobcat populations. Bobcat harvests did increase during 1976–1984, but recent harvest levels are comparable to those three decades earlier (36,674 harvested during 1997–1998 verses 37,026 during 1975–1976), despite this increase in population size (Association of Fish and Wildlife Agencies, unpublished data). This is likely due to decreased harvest effort.

Because population survey methods were not standardized across jurisdictions, there is likely substantial variability in the accuracy of the estimates provided by management agencies. For example, only six states used any form of population model in their monitoring of bobcat populations, likely because of the paucity of accurate data available for developing such models. Similarly, 19 states failed to report population estimates. Although this variability may be substantial, it does not preclude comparison to previous reports (USFWS 1982) or interpretation of jurisdiction-specific population trends. Agency surveys such as this provide the only feasible means of providing range-wide population assessments, because field-based surveys would be logistically and financially impractical. Although the level of detail in such surveys is limited, they can provide a cost-effective means to estimate large-scale population trends. At the statewide scale, harvest surveys were the most commonly used approach for monitoring bobcat populations, which is not surprising given that these data can be obtained for large geographic areas at relatively low costs. Unlike harvest analysis or scent stations, methods such as hunter surveys that do not require market-based incentives or extensive field labor may be more practical methods for monitoring bobcat population trends.

As with many species, enumeration of population abundance is not required for proper management. Within jurisdictions, specific monitoring programs can be implemented if needed. In the United States, 41 states currently monitor bobcat population status or trends, despite the fact that only one state reported bobcat populations as declining. Population models, archer surveys, hunter surveys, harvest data, field studies, scent-post surveys, sign-station surveys, public sightings, and detection dogs are all techniques used in North America to monitor bobcat populations (Bluett et al. 2001; Anderson and Lovallo 2003). The majority of jurisdictions that reported monitoring methods used multiple methods (Table 2). The number of jurisdictions monitoring bobcat populations, and the number of methods used, is similar to previous reports (Woolf and Hubert 1998). The number of jurisdictions reporting increasing bobcat populations has increased from 20 to 32 since 1996 (Woolf and Hubert 1998), and overall population estimates for the United States have more than doubled since 1981 (USFWS 1981). Similarly, six of the seven Canadian provinces reported stable bobcat populations.

Bobcat populations are more widely distributed and more abundant than they were in 1981. These increases are likely attributable primarily to multiple factors including habitat availability, increased prey density, changing land-use practices, and intense harvest management at the state level. Standardization of monitoring and density-estimation techniques would increase the robustness of future comparisons. Thus, we suggest that jurisdictions focus on developing standardized methods for assessing bobcat distribution and abundance.

Acknowledgments

We thank the state, provincial, and national wildlife management agencies for providing the data for this analysis. The Ohio Division of Wildlife facilitated the distribution and collection of the surveys. Logistical support was provided by the Department of Natural Resources at Cornell University and the Department of Forest Management at the University of Montana. We also thank the two anonymous reviewers and the Subject Editor for providing valuable comments that improved the quality of the manuscript.

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Author notes

Nathan M. Roberts,* Shawn M. Crimmins

Roberts NM, Crimmins SM. 2010. Bobcat population status and management in North America: evidence of large-scale population increase. Journal of Fish and Wildlife Management 1(2):169–174; e1944-687X. doi: 10.3996/122009-JFWM-026