Spacing Behavior and Movements of the American Black Bear (Ursus

Home , American black bear, Sequoia sempervirens

INTRASPECIFIC BLACK BEAR SPATIAL PATTERNS AND INTERACTIONS AT

A SMALL SPATIO-TEMPORAL SCALE

Desiree A. Early

A Thesis

Presented to

The Faculty of Humboldt State University

In Partial Fulfillment

Of the Requirements of the Degree

Master of Science

In Natural Resources: Wildlife

February, 2010

ABSTRACT

INTRASPECIFIC BLACK BEAR SPATIAL PATTERNS AND INTERACTIONS AT A SMALL SPATIO-TEMPORAL SCALE

Desiree A. Early

Understanding intraspecific spatial patterns and interactions of American black bears (Ursus americanus) can improve the understanding of social behavior and management of the species. Few studies have examined spatial patterns of American black bears at small spatial and temporal scales. Sixteen black bears (8 females and 8 males) were radio-collared between 27 May and 12 August 2008 in a 175 km2 study area in Humboldt County, California. I measured home range size, overlap, and overlap frequency to describe static spatial patterns (without a temporal component). I measured the spatial and temporal interactions of groups of bears by examining distances between bears and of pairs of bears by examining the use of home range overlapping areas. The mean 95% fixed-kernel home-range estimate was larger for males than for females.

Females overlapped other bears with a greater percentage of their overall home range than males. Male home ranges overlapped other bears with a greater frequency than females. According to the spatial and temporal interaction analysis based on distances between bears, bears were not moving in response to neighboring bears. Spatial and temporal interactions occurred for 24% of the pairs of bears utilizing home range overlapping areas, with 18% exhibiting a significant spatial interaction and 6% exhibiting a significant temporal interaction. Although spatial and temporal interactions occurred between eight pairs of bears, spatial and temporal interactions were not detected for 26 pairs of bears in the study area. The lack of significant spatial and temporal interactions

iii

may be a result of high black bear densities. Alternatively, bears within the study area may be interacting at a much finer scale (i.e., within food patches) than this study was able to detect.

ACKNOWLEDGMENTS

I thank my advisor Dr. Richard Golightly for his guidance and support throughout the process. I also thank my committee members Dr. Richard Brown and Dr. Micaela

Szykman Gunther for their thoughtful comments and criticisms during the design and review of this project. This project would not have been possible without the telemetry and field equipment I borrowed from my advisor, Dr. Matt Johnson, and Green Diamond

Resource Company. I especially thank Lowell Diller, Keith Hamm, and Pat Zimmerman for helping with the design and implementation of the black bear project and for providing the black bears. I thank Dr. Howard Stauffer, Dr. Mark Rizzardi, and Tom

Gorman for assistance and advice with data analyses. I am also grateful to the many volunteers who spent countless hours standing on hills in the rain listening to beeps.

Those people include: Jacob Bagnell, Ryan Bourque, Kristin Brzeski, Tiffany

Concannon, Noelani Davis, Dan Fidler, Lindsy Greene, Jillian Jackson, Ryan

Kalinowski, Brendan Lynch, Angela Moran, Aicha Ougzin, Shad Scalvini, Carmen

Vanbianchi, and Pat Zimmerman. I am also grateful for my only other sources of funding provided by Richard Callas and the California Department of Fish and Game and the

Marin Rod and Gun Club Scholarship. I dedicate this thesis to my parents, Troy and

Mona Early, for their understanding, support, and encouragement.

TABLE OF CONTENTS

Page

ABSTRACT ...... iii

ACKNOWLEDGMENTS ...... v

LIST OF TABLES ...... viii

LIST OF FIGURES ...... ix

LIST OF APPENDICES ...... x

INTRODUCTION ...... 1

STUDY AREA ...... 5

MATERIALS AND METHODS ...... 7

Capture and Handling ...... 7

Home Range Analysis...... 9

Spatial and Temporal Interaction Analysis ...... 11

Bear-to-bear distances ...... 11

Home-range overlap areas ...... 12

RESULTS ...... 17

Home Range Analysis...... 17

California, 2008. Spatial and Temporal Interactions ...... 21

Spatial and Temporal Interactions ...... 18

Bear-to-bear distances ...... 18

Home-range overlap areas ...... 23

DISCUSSION ...... 25

LITERATURE CITED ...... 34

APPENDICIES ...... 42

vii

LIST OF TABLES

Table Page

1 Description of notation used in text for calculating the spatial and temporal interactions between black bears within home range overlapping areas in the Little River study area in northwestern California, 2008...... 13

2 Percent overlap and frequency statistics for 7 female and 3 male black bears in the Little River study area in northwestern California, 27 May- 12 August 2008...... 20

viii

LIST OF FIGURES

Figure Page

1 Location of the Little River study area, surrounding cities, and Green Diamond Resource Company (Green Diamond) ownership for the study of black bear spatial patterns in Humboldt County, California, 2008...... 6

2 Fixed-kernel home-range estimates of 7 female and 3 male black bears in the Little River study area in northwestern California, 2008. Boxes represent ±1 SE, horizontal lines within the boxes represent the mean, and the vertical lines represent the range...... 19

3 Spatial distribution representing maximum home-range overlap of 70% for female 3 with female 20 in the Little River study area in northwestern California, 2008...... 21

4 Observed and expected distances between pairs of bears (n=70 pairs of bears) pooled by sex for 16 black bears (8 females and 8 males) in the Little River study area in northwestern California, 2008...... 22

5 Significant spatial and temporal interactions of 8 pairs of black bears consisting of 6 females and 2 males within the shared home range overlap areas in the Little River study area in northwestern California, 27 May- 12 August 2008. Arrows indicate type and direction of interactions...... 24

LIST OF APPENDICES

Appendix Page

A. Sex, weight, and age for collared bears (n=16) in the Little River study area in northwestern California, 2007-2008...... 42

B. Bootstrap analysis for 8 female and 8 male black bears in the Little River study area in northwestern California, 2008. Curved line represents minimum number of telemetry locations to obtain an accurate home range size...... 43

INTRODUCTION

Knowledge of intraspecific spatial patterns (here after spatial patterns) and interactions of American black bears (Ursus americanus) is essential for the successful management of the species. Information regarding the intraspecific spatial and temporal relationships is necessary to understand social behavior among individuals (Chamberlain and Leopold 2000). Spatial and temporal interactions among American black bears are influenced by food abundance (Powell 1987, Elowe and Dodge 1989, Schooley et al.

1994, Rudis and Tansey 1995, Samson and Huot 2001), topography (Amstrup and

Beecham 1976, Reynolds and Beecham 1980), kinship (Garshelis and Pelton 1981,

Clevenger and Pelton 1987, Rogers 1987, Schwartz and Franzmann 1992, Moyer et al.

2006), and social dominance (Garshelis and Pelton 1981, Beckmann and Berger 2003).

Topography and the distribution and availability of resources impact bear movements (Amstrup and Beecham 1976, Reynolds and Beecham 1980, Garshelis and

Pelton 1981). Black bears may move in response to changes in food availability at different elevations that may be correlated with climate or other seasonal changes

(Amstrup and Beecham 1976, Reynolds and Beecham 1980). Black bears from the same watershed in the Great Smoky Mountains National Park responded to elevational changes in food availability (Garshelis and Pelton 1981). In addition, observations of intraspecific tolerance has been reported among foraging females (Amstrup and Beechan 1976, Rogers

1987). Concentrated food sources, such as garbage dumps, may also decrease bear-to- bear distances (Herrero 1983, Rogers 1987).

Black bear spatial patterns are affected by behavioral characteristics associated with kinship and social dominance. Kinship influences bear spatial patterns in that related females tend to be spaced closer together than unrelated females (Moyer et al. 2006).

After the young disperse, some female black bears reassociate with their offspring

(Jonkel and Cowan 1971, Rogers 1987, Clevenger and Pelton 1987, Schwartz and

Franzmann 1992, Lee and Vaughan 2004). Instances of yearling reassociations have also been reported (Ternent and Garshelis 1998).

Social dominance can be influenced by size, age, and gender (Beckmann and

Berger 2003). For example, black bears in the boreal forests of Alberta displayed signs of intrasexual territoriality (Young and Ruff 1982). In Washington, older and larger male bears were dominant over younger and smaller males (Lindzey and Meslow 1977).

Dominant males chased younger and smaller subordinate males, and subordinate males avoided dominant males by using alternative travel routes. Male bears in Washington were dominant over females during the breeding season, whereas the dominance structure among females was based mainly upon age (Lindzey and Meslow 1977).

Social dominance may also limit some black bear populations (Lecount 1982,

Young and Ruff 1982). The removal of large adult male bears may lead to local population increases if the large adult males limit sub-adult recruitment (Young and Ruff

1982). Similarly, Lecount (1982) speculated that adult female black bears may be potential predators of cubs. These internal population control mechanisms may help managers predict potential consequences of black bear harvest strategies or depredation actions. For example, spatial patterns and social interactions may provide insight about

3 population control methods in areas where bears are damaging large numbers of trees

(Hosack and Fulgham 1996).

Black bears damage trees by partial or complete girdling which may result in reduced growth, increased susceptibility to infection, or death of the tree (Hosack and

Fulgham 1996). One black bear may damage up to 70 trees per day, and economic loss on private timberlands due to black bear tree damage in the Pacific Northwest has been estimated annually at 5 million dollars (Ziegltrum and Nolte 2001). Adult female black bears have been implicated as the sex and age class most prone to damaging trees while larger male bears are less likely to damage trees (Stewart 1997, Collins et al. 2002). If larger, older male bears limited female recruitment to an area, then the removal of the larger, older male might result in an increase in female bears and thus a potential increase in tree damage. Therefore, spatial patterns of black bears can provide knowledge of social dominance and help guide management decisions regarding black bear harvest strategies or depredation actions.

Few studies (Rogers 1987, Schenk et al. 1998, Samson and Huot 2001) have focused on black bear spatial patterns at small spatial and temporal scales (i.e. interactions within a portion of the home range, within a single season, or interactions based on simultaneous locations). The literature on bear-to-bear interactions has been based on frequency of home range overlap alone (Amstrup and Beecham 1976, Garshelis and Pelton 1981, Schenk et al. 1998), observations of a few individuals (Amstrup and

Beecham 1976, Lindzey and Meslow 1977, Horner and Powell 1990, Lee and Vaughan

2004), or observations of one gender or age class within a population (Samson and Huot

1998, Schenk et al. 1998, Samson and Huot 2001, Moyer et al. 2006). Therefore, I examined spatial and temporal interactions (interactions between two animals within a shared area and across time) for multiple age and gender classes at a small spatiotemporal scale.

My objectives were to document black bear 1) home-range size, 2) percent home- range overlap, and 3) frequency of home-range overlap. I also attempted to describe 4) spatial and temporal interactions among individuals by examining home range overlap areas (Minta 1992), and 5) spatial and temporal interactions among groups of bears by examining bear-to-bear distances (Kernohan et al. 2001). Two methods were used to describe black bear spatial and temporal interactions in order to overcome the limitations of both methods. The method based on home range overlap areas has a higher sensitivity to detecting interactions between pairs of bears, but the method requires large sample sizes. The second method based on bear-to-bear distances provides generalized interactions among groups of bears, but the method does not require as large a sample size and is not limited to home range overlap areas. The method based on home range overlap areas will describe how pairs of bears share space, and the method based on bear- to-bear distances will describe the distances between bears in relation to an expected value that is based on random movements.

STUDY AREA

The study was conducted in the Little River watershed in Humboldt County,

California in the north coast redwood zone where fog is common. Mean summer and winter temperatures within the study area are about 18˚C and 5˚C, respectively.

Precipitation ranges from 102-254 cm annually with 90% falling from October to April.

Topography is characterized by steep slopes and rugged terrain (Thome et al. 1999).

The study area was bordered by Highway 101 to the west, U.S. Forest Service land to the east, McKinleyville, California to the south, and Redwood National and State

Parks to the north. Elevation ranged from 30-2080 m. Dominant tree species included coast redwood (Sequoia sempervirens) and Douglas-fir (Pseudotsuga menziesii) (Galea

1990). The study area was 175 km2 and located within the 361 km2 Big Lagoon and Little

River Timber Tracts owned by Green Diamond Resource Company (Figure 1). The study area was dissected by multiple logging roads and was in a mixture of vegetative successional stages due to historic logging (Galea 1990).

Figure 1. Location of the Little River study area, surrounding cities, and Green Diamond Resource Company (Green Diamond) ownership for the study of black bear spatial patterns in Humboldt County, California, 2008.

MATERIALS AND METHODS

Capture and Handling

Bears were captured between May 2007 and May 2008 in culvert traps set along easily accessible roads and baited with bacon grease, dog food, or fish. Traps were checked twice daily. Captured bears were immobilized with an intramuscular injection of ketamine (≈4.4 mg/kg) and xylazine (≈2.2 mg/kg) administered by jab stick using a 16- gauge needle. Weight was estimated by experienced personnel prior to injection. After immobilization, bears were marked with individually numbered plastic Fearing Hog

Litter ear tags (Fearing Corporation, South St. Paul, Minnesota) and passive integrated transponders (PIT tags) implanted subcutaneously behind the base of the right ear. Bears were placed on a stretcher and attached to a hanging scale to obtain an actual weight

(recorded to the nearest kg). Bear weights were compared for males and females using a two-tailed t-test with a significance level of 0.05 (Zar 1999). A first upper premolar was extracted from each bear and aged by cementum annuli (Willey 1974, Matson’s

Laboratory, Milltown, Montana).

Bears were radio-collared with mortality-sensitive transmitters (Telonics,

Arizona, MOD-500(NH) and ATS, Minnesota, M2520B). Young bears that had the potential to out-grow their collar size were collared with break-away collars. Male bears weighing less than 40 kg and females weighing less than 30 kg were not radio-collared.

After a minimum of 40 minutes elapsed from the time of immobilization, bears were given an intravenous injection of yohimbine (0.15 mg/kg) to reverse the effects of the

8 xylazine. Bears were allowed to recover from the anesthesia for 30 to 90 minutes inside the culvert trap before being released. Capture and handling procedures were approved by the Humboldt State Animal Care and Use Committee (protocol No. 06/07.W.208-A).

I attempted to capture all bears residing in the Little River study area in order to obtain an accurate representation of spatial patterns and movements relative to neighboring bears (Samson and Huot 2001). In order to determine what proportion of the population in the study area had been marked with radio collars, 20 camera tubes were placed throughout the study area (Arias 2007). Each camera tube consisted of a plastic culvert with a length of 1.2 m and a diameter of 0.4 m. The bottom of the culvert was fitted with a pressure triggered treadle that would trigger a 35-mm camera placed in the back of the culvert. The camera tubes were baited with a raw chicken leg hanging from the center of the culvert. Each photograph was automatically labeled with the time and the date. Camera tubes were in operation from August 15, 2007 until January 20, 2008.

Camera tube maintenance was conducted three to four times per week to check batteries, film, and bait, and to fix mechanical problems.

Photographs were examined for the presence of bears. I collected information on the number of bears with and without collars or ear tags. Notes were made about bear size, bear color, and any other identifying characteristics, such as scars or other natural markings, in order to distinguish between individuals and prevent overestimations.

Camera tube observations were used to calculate the proportion of collared bears to total bears (collared bears / (non-collared + collared bears)) and multiplied by 100 to obtain a percentage of collared bears present in the Little River study area.

Home Range Analysis

Locations for each collared bear were collected from 27 May until 12 August

2008 to coincide with the breeding season. Simultaneous locations were obtained for multiple bears using standard techniques for triangulation (White and Garrott 1990,

Samuel and Fuller 1996). Telemetry error was estimated by triangulating on blind test collars placed in known locations. Telemetry error was calculated as the average linear error between the estimate and the actual location (White and Garrott 1990, Millspaugh and Marzluff 2001).

Six permanent telemetry stations were established at high elevation locations along the perimeter of the study area, and individuals with telemetry equipment were distributed among the stations. Each day, teams of three to six people simultaneously collected azimuths from their respective stations to obtain locations for all available bears in the Little River study area. Simultaneous locations were defined as those collected within the same one-hour period. Since animal movement can greatly reduce telemetry accuracy (Schmultz and White 1990), relocations that had greater than 30 minutes between first and last azimuths were not used in analyses (Van Etten et al. 2007).

Simultaneous telemetry locations were collected for all available bears in the Little River study area once per day for three to four days per week between 0800 h and 1300 h. A minimum of three azimuths were used for triangulation and estimating a bear’s location.

All locations were plotted using the Location of a Signal (LOAS) 4.0 software

(Ecological Software Solutions, Sacramento, California), and analyzed using ArcGIS

10 software (ArcGIS Version 9.3, Environmental Systems Research Institute, Redlands,

California). All locations with overlapping error polygons (polygon created by the intersections of the telemetry azimuths) or with error polygons exceeding 10 km2

(approximately half of a female’s mean home-range size) were excluded from further analyses.

I attempted to obtain at least 30 independent locations for each bear throughout the study period to determine home ranges (Koehler and Pierce 2003). The minimum number of locations necessary to obtain an accurate home range size was determined by conducting a bootstrap test that plotted estimated home range size against sample size using the Animal Movements Extension (ArcView Version 3.2, Environmental Systems

Research Institute, Redlands, California). All locations were separated by 24 h to ensure independence. A 95% contour home range was estimated using the fixed kernel method with a smoothing parameter of 1500 (Worton 1989, Schwartz et al. 2006). The smoothing parameter of 1500 was smaller than the least-squares cross validation estimate which overestimated home-range size. A conservative smoothing parameter was selected to decrease errors in the interaction analysis between home-range overlap areas. Home range sizes were compared for males and females using a two-tailed t-test with a significance level at 0.05 (Zar 1999).

Percent overlap was calculated by dividing the area of overlap by the total home range area and multiplying by 100. Percent overlap was calculated for each pair of bears with overlapping home ranges. Frequency of overlap was calculated as the total number

11 of overlapping individuals. For example, one bear’s home range may overlap with five other bear home ranges yielding a frequency of five.

Spatial and Temporal Interaction Analysis

Bear-to-bear distances

Interactions based on simultaneous locations maintain the serial correlation in location data, therefore explaining the spatial and temporal aspects of one animal’s influence on another individual (Kernohan et al. 2001, Gorman et al. 2006). Spatial and temporal interactions between two individuals were calculated if some portion of the 95% fixed-kernel home range overlapped with another individual (Gorman et al. 2006) or if the two home ranges were within a 300 m buffer (approximation of telemetry error) from one another. Only distances between pairs of bears with five or more simultaneous locations were used in the analysis. Based on guidelines from Kernohan et al. (2001), I calculated the observed distance (Do) as:

where x1 and y1, and x2 and y2 (over all cases of j ) are the universal transverse mercator coordinates for animals 1 and 2, respectively, for n pairs of locations. The expected distance (DE) considers all distances between all recorded observations (over all cases of j and k) and was calculated as:

I pooled interactions by sex and compared the difference between observed and expected distances using a Wilcoxon signed-rank test (Zar 1999, Gorman et al. 2006). If the pooled observed distances were significantly different (p< 0.05) from the expected distance, bears were interacting by maintaining distances closer than would be expected if bears were moving at random (attraction) or by maintaining distances further apart than would be expected if bears were moving at random (avoidance). If the pooled observations were not significantly different from the expected distance, bears were considered to be moving at random relative to each other (no interaction).

Home-range overlap areas

I used the method proposed by Minta (1992) to determine spatial and temporal interactions between pairs of bears that shared a common area (home-range overlap area).

I tested the null hypothesis that for a pair of bears, bear α and bear β (Table 1), sharing a home-range overlap area, each bear would use the home-range overlap area spatially and temporally independent of the other (random movement) (Minta 1992, Mace and Waller

1997, Samson and Huot 2001). Simultaneous locations for each pair of bears that used overlapping home-ranges were placed into one of the following categories of observed frequencies: 1) both individuals were absent simultaneously from the overlapped area

(n11); 2) only individual α was present in the overlapped area (n21); 3) only individual β was present in the overlapped area (n12); 4) both individuals were present simultaneously in the overlapped area (n22). Then I summed the observed frequencies (Table 1) of

Table 1. Description of notation used in text for calculating the spatial and temporal interactions between black bears within home range overlapping areas in the Little River study area in northwestern California, 2008.

Term Description

  Animal "A"

β Animal "B"

Observed frequencies

n11 Both  and β simultaneously present in overlap area n12 Only β simultaneously present in overlap area n21 Only  simultaneously present in overlap area n22 Both  and β simultaneously absent from overlap area n+1 Sum of observed simultaneous sightings of  and β in the overlap area n+2 Sum of observed simultaneous sightings of only β in the overlap area n1+ Sum of observed simultaneous sightings of only  in the overlap area n2+ Sum of observed simultaneous sightings of  and β absent from overlap area

Expected frequencies (probabilities)

p11 Both  and β simultaneously present in overlap area p12 Only β simultaneously present in overlap area p21 Only  simultaneously present in overlap area p22 Both  and β simultaneously absent from overlap area p+1 Sum of expected simultaneous sightings of  and β in the overlap area p+2 Sum of expected simultaneous sightings of only β in the overlap area p1+ Sum of expected simultaneous sightings of only  in the overlap area p2+ Sum of expected simultaneous sightings of  and β absent from overlap area

14 presence and absence for each animal. The expected frequencies (Table 1) were based on the proportion of overlapped area to total home range area. The expected frequencies of presence and absence were also summed. Observed frequencies of presence and absence for each animal were compared to expected frequencies to form an overall chi-square

2 (χ tot). If bear  and bear β were using the home-range overlap area independently of one another as predicted by the expected frequencies, then

should be small with three degrees of freedom (df) and n equal to all simultaneous

2 observations of bear  and β. I partitioned the χ tot into three parts (spatial main effect of bear , spatial main effect of bear β, and one temporal interaction effect). The “effect” was the combination of a spatial coefficient ( or ) or temporal interaction

2 coefficient (Lixn) and a χ probability value. The three partitions with corresponding coefficients and χ2 probability values (effects) were as follows:

Spatial main effect of bear ; df = 1:

Spatial main effects of bear β; df = 1:

Temporal interaction effect; df = 1:

The two spatial main effects denoted each animal’s spatial association with the shared home-range overlap area and was represented by the coefficients and . The results were then translated into terms of spatial attraction to or avoidance of the shared home-range overlap area. The temporal interaction effect denoted each animal’s temporal association with the spatial use of the shared home-range overlap area and was represented by the coefficient Lixn. The results were then translated into terms of the pair’s simultaneous versus solitary occupation of the shared home-range overlap area relative to the overall home range use (temporal attraction or avoidance of the shared overlap area).

For each pair of bears, probability values were derived from the chi-square test statistics from each of the three partitions. For each significant interaction (p<0.05), the

16 spatial main effect coefficients and the temporal interaction coefficients were examined to interpret the results for each significant bear pair as exhibiting spatial attraction, spatial avoidance, temporal attraction, temporal avoidance, or random movements. When the spatial main effect coefficients and approached zero, use of the shared home-range overlap area became random. When the coefficients were greater than zero, the individuals were attracted to the shared home-range overlap area, and when the coefficients were less than zero, the individuals avoided the shared home-range overlap area. When the temporal interaction coefficient Lixn was greater than zero, both individuals were using the overlap area simultaneously (temporal attraction), and when

Lixn was less than zero, only one individual used the overlap zone at a time (temporal avoidance). Following Mace and Waller (1997) and Samson and Huot (2001), the spatial and temporal interaction results were further classified as symmetrical (same spatial/temporal response by the pair), asymmetrical (opposite spatial/temporal response by the pair), or singular response (only one individual showed a response).

After examining the significant spatial and temporal interactions and determining the directionality of each interaction (attraction or avoidance) the odds ratio, or departure from expectation, of each of the four categories of observed frequencies (n11, n21, n12, n22) and expected frequencies (p11, p21, p12, p22) was used to interpret the magnitude or intensity of the significant interactions. Since there are three ways to be solitary (i.e., one or the other or both animals exhibiting avoidance), the odds ratios allowed for a more detailed interpretation of the significant spatial and temporal interactions (Minta 1992).

RESULTS

In the 175 km2 Little River study area, 36 bears (10 females, 26 males) were radio-collared between May 2007 and June 2008. However, only 24 bears (9 females, 15 males) remained available during the 27 May to 12 August 2008 study period. Of the 24 available bears, only 16 (8 females, 8 males) were located consistently (≥ 5 locations) yielding 258 usable telemetry locations.

Camera tubes were in operation from August 15, 2007 until January 20, 2008

(after the trapping period) for a total of 2,971 camera nights. Based on the proportion of collared (n=2) to total (n=10) bears photographed by the camera tubes, 20% of the bears in the Little River study area were radio-collared. Telemetry error calculated as average linear error between the estimate and the actual location was 230±44 m ( ±SE). Captured bears (n=39) averaged 84±6 kg (range= 39-186 kg). Collared bears (n=16) averaged 75±5 kg (range= 48-123 kg) with males (89±7 kg) larger than females (62±4 kg) (t= 3.41, df=14, P < 0.02). Average age for collared bears was 3.9 years and ranged from 2-6 years

(Appendix A). Due to the small range in age classes, age was not included in analyses.

Home Range Analysis

According to the bootstrap test, greater than or equal to 25 locations per bear were needed to estimate home ranges (Appendix B). Due to the low number of collared males and male locations, bears with greater than 10 locations were included in home range

18 analyses. Fixed-kernel home-range estimates were compared for 10 bears (7 females and

3 males) of the 16 bears used in the overall study. The mean 95% fixed-kernel home- range estimate was larger for males than for females (t = 2.31, df= 8, P < 0.05, Figure 2).

Percentage of home range overlap between females was 38.1±3.4% (Table 2). Females and males overlapped each other with 30.4±2.8% of their total home ranges. Home range overlap between males was 21.1±4.0% (Table 2). The largest home range overlap occurred between two females where one female (F3) overlapped another female (F20) with 71% of her total home-range (Figure 3).

Males had greater home range overlap frequencies than females (Table 2). Home ranges of each female overlapped with at least five other bears, and male home ranges overlapped with at least seven other bears. Female and male home ranges overlapped with at least two bears of the same sex, and each male overlapped with at least five of the seven females.

Spatial and Temporal Interactions

Bear-to-bear distances

Observed distances were calculated for 16 bears (8 females, 8 males) yielding observations for 70 pairs of bears. The observed distances between female-female (Z=

0.943, P>0.1, n=23), female-male (Z= 1.082, P>0.1, n=41), and male-male (Z= 0.524,

P>0.1, n=6) were not significantly different from the expected (Figure 4).

Figure 2. Fixed-kernel home-range estimates of 7 female and 3 male black bears in the Little River study area in northwestern California, 2008. Boxes represent ±1 SE, horizontal lines within the boxes represent the mean, and the vertical lines represent the range.

Table 2. Percent overlap and frequency statistics for 7 female and 3 male black bears in the Little River study area in northwestern California, 27 May- 12 August 2008.

Female-female Male-male Female-malea All pairs

Percent overlap

± SE 38.1 ± 3.4 21.1 ± 4.0 30.4 ± 2.8 32.8 ± 2.1

Range 9.0-71.0 8.5-30.4 1.0-61.7 1.0-71.0

Overlap frequency

± SE 3.4 ± 0.6 2.0 3.8 ± 0.6 6.7 ± 0.5

Range 2.0-7.0 - 2.0-7.0 5.0-9.0 a Comparisons made between opposite sexes only.

Figure 3. Spatial distribution representing maximum home-range overlap of 70% for female 3 with female 20 in the Little River study area in northwestern California, 2008.

Figure 4. Observed and expected distances between pairs of bears (n=70 pairs) pooled by sex for 16 black bears (8 females, 8 males) in the Little River study area in northwestern California, 2008.

Home-range overlap areas

Of the 34 pairs of bears with shared home range overlap areas, 8 pairs (24%) exhibited significant spatial or temporal interactions. In six (18%) of the 34 pairs, spatial use of the home range overlap area was significantly (P<0.05) different from random

(Figure 5). Temporal use of the home range overlap area was also significantly (P<0.05) different from random for two (6%) of the 34 pairs of bears (Figure 5). Except for one male-female pair that exhibited temporal attraction, all significant spatial and temporal interactions were singular responses, and only females exhibited responses (Figure 5).

Spatial avoidance interactions were not detected among the 34 pairs, and all male-male

(n= 3) associations were random (P>0.05).

Figure 5. Significant spatial and temporal interactions of 8 pairs of black bears consisting of 6 females and 2 males within the shared home range overlap areas in the Little River study area in northwestern California, 27 May- 12 August 2008. Arrows indicate type and direction of interactions.

DISCUSSION

Consistent with previous studies (Pelton 2003, Powell et al. 1997, Koehler and

Pierce 2003), male black bears had larger home ranges than female black bears. Because black bears are induced ovulators (Whimsatt 1963), the first male to mate with an estrous female would have an advantage over other males (Kovach and Powell 2003). Also, males that have high encounter rates with females can have higher reproductive success

(Kovach and Powell 2003). Therefore, male black bears might maintain a large home range to increase access to estrous females (Powell et al. 1997, Koehler and Pierce 2003).

Size comparisons between home ranges in the Little River study area and those reported from other studies are complicated by differences in methodology (i.e. sample size, duration and season of monitoring effort, and estimator used to calculate home ranges) (Young and Ruff 1982, White and Garrott 1990, Koehler and Pierce 2003). Male home ranges in the Little River study area were much smaller than the annual 95% fixed- kernel home ranges reported for male black bears in Washington (Koehler and Pierce

2003). However, those authors did not experience the same problems with sample sizes.

For example, males were often located outside of the Little River study area which decreased telemetry accuracy or made locations impossible to acquire from the permanent telemetry stations. Therefore, home ranges reported in this study for male black bears represent the minimum area for home ranges. The difficulties in locating males outside of the study area also contributed to the overall low number of locations used for calculating male home ranges. Female home ranges were similar to the annual

95% fixed-kernel home ranges reported in Washington (Koehler and Pierce 2003) and

Florida (Moyer et al. 2006).

Although males maintained larger home ranges than females, female black bears overlapped other bears with greater percentages of their home ranges. However, males overlapped females with a greater frequency. The three male black bears in the Little

River study area whose home ranges were estimated despite having fewer locations than required by the bootstrap analysis overlapped with at least five of the seven collared females. Female black bears exhibited a similar overlap frequency to females studied in

Florida by Moyer et al. (2006). However, the frequency estimates found in the Little

River study area likely reflect the minimum level of home-range overlap within the population because not all bears in the study area were radio-collared (Moyer et al. 2006).

Large home ranges and high levels of home range overlap are probably important factors in male black bear mating strategies (Powell et al. 1997, Koehler and Pierce

2003). However, resource availability may be more of a contributing factor to maintaining larger overlapping areas for female black bears (Powell 1987). Little to no home-range overlap has been reported among females in areas where food abundance is low (Jonkel and Cowan 1971, Young and Ruff 1982, Rogers 1987). Contrastingly, extensive home-range overlap has been reported in areas of higher food abundance

(Powell 1987, Horner and Powell 1990).

Based on spatial and temporal interactions analysis within home range overlap areas, only 24% of the pairs of bears in the Little River study area exhibited significant interactions. In a study conducted in eastern Canada using similar methods, Samson and

Huot (2001) observed significant spatial interactions among 59% of the female black bear pairs in their study population. Contrastingly, only 18% of the pairs of bears in the Little

River study area exhibited significant spatial interactions. The majority of significant interactions were only spatial or only temporal and mostly singular responses. Similarly, the spatial and temporal interactions analysis based on distances between bears suggested bears in the Little River study area were moving at random and not in response to neighboring bears.

Small sample sizes (e.g., few collared bears and few locations) might explain the lack of significant spatial and temporal interactions. Only 36 bears were collared in the study population, and only 16 bears had adequate sample sizes for inclusion in analyses.

Therefore, movements and interactions of the collared bears were most likely confounded by the non-collared bears present in the study area (Minta 1992). If a higher percentage of bears in the study population had been collared, I might have detected a higher number of significant interactions.

The lack of demographic diversity among collared bears might also explain the lack of spatial and temporal interactions. Several large males weighing greater than 113 kg were captured and collared in the beginning of the study. However, attaching collars to large males was problematic due to their drastic seasonal weight loss and weight gain throughout the study. As a result, all of the larger males lost their collars before adequate data could be collected. Similarly, trapping and telemetry efforts resulted in a bias towards young adults (age 3 to 4), females, and smaller males.

In northern California, coastal bear populations have been estimated between 0.5 and 2.0 bears/km2 (Kellyhouse 1977, Arias 2007). Inland populations have been estimated between 0.2 and 1.3 bears/km2 (Matthews et al. 2008). My study was not designed to estimate black bear densities; however, I estimated that 20% of the bears were collared suggesting that the black bear density in the Little River study area was about 1 bear/km2. This rough density estimate supports the high black bear density claims of the other studies in northwestern California. Black bear densities in northern California are higher than densities reported in central Arizona (Lecount 1982), western Oregon

(Immell and Anthony 2008), Alaska (Miller et al. 1997), Louisiana (Boersen et al. 2003),

Alberta Canada (Young and Ruff 1982), and a number of other locations throughout

North America.

The lack of significant spatial and temporal interactions might be explained by the high density of black bears. In response to the high black bear densities and the high levels of home range overlap, bears in the Little River study area might not invest time and energy in securing exclusive use of a concentrated food source (Rogers 1987,

Samson and Huot 2001). In the absence of exclusive use or territoriality, social dominance structures would regulate access to resources (Rogers 1987). For example, older and larger individuals would have unencumbered access to prime resources while less dominant younger and smaller individuals would need to coordinate access in response to the presence or absence of the more dominant individuals. When food resources and competitors are abundant, the cost of defense increases (Krebs and Davies

1993). For this population, the cost may be greater than the benefit due to the high black

29 bear densities and food abundance. Therefore, spatial and temporal interactions based on a dominance structure may not be cost effective for the Little River population.

Although certain black bear pairs exhibited significant spatial or temporal interactions, the majority of interactions, such as avoidance or attraction based on a social dominance structure, may be occurring at a much finer scale than I was able to study (i.e., within food patches). A few observations of black bears during other studies have provided examples of these interactions within food patches. For example, foraging females and subadult males have been observed in close proximity of the same food patch without exhibiting antagonistic behavior (Amstrup and Beecham 1976, Young and

Ruff 1982, Rogers 1987). In addition, adult males have been observed chasing subordinate males and females away from prime food resources (Lindzey and Meslow

1977).

It is likely that similar fine scale interactions are occurring in the Little River study area; however, technological, visual, and topographical limitations prevented fine scale observations. The fine scale interactions within food patches, such as the presence of a large male causing a small male to leave a feeding area, occur almost instantaneously

(fine temporal scale). In order to use telemetry to capture the instantaneous interactions between bears, one would need to obtain enough simultaneous, serial locations (a few minutes apart) with small locational error to be able to infer one bear’s response to the presence of another bear. Standard very high frequency (VHF) radio telemetry technology lacks fine scale spatial and temporal resolution. Recent advances in global positioning system (GPS) telemetry have greatly increased accuracy of telemetry

30 locations over conventional VHF telemetry. However, GPS telemetry technology has also been limited in obtaining the fine spatial and temporal scale needed to observe interactions within food patches. While GPS locations may be taken simultaneously and serially, the topographic limitations within the study region increase the locational error, and the high equipment costs associated with GPS telemetry limit the ability to obtain large sample sizes. Similarly, the rugged terrain and dense understory make direct visual observations almost impossible.

While the spatial and temporal interaction analysis based on distances between bears showed no interactions among groups of bears, some black bear pairs were moving in response to neighboring bears based on the interaction analysis within home range overlapping areas. Among the few significant interactions, two of eight females were spatially attracted to the overlap areas they shared with a third female. Resource availability might be one explanation for this spatial attraction (Young and Ruff 1982,

Pelchat and Ruff 1986, Rogers 1987). The third female weighed 16 kg more than the other two females and was also one year older with possibly a more established home range than the other two females. Therefore, her home range might have included prime food resources that attracted the two younger females. Relatedness is not a likely explanation for this spatial attraction because the three females were too close in age to be mother-daughter pairs and not close enough in age to be yearlings from the same litter.

Alternatively, relatedness may explain the spatial attraction exhibited between a different pair of females that had an age difference of four years. After dispersal, female yearlings may establish home ranges near or within a portion of the mother’s home range

(Rogers 1987, Moyer et al. 2006). Therefore, relatedness may influence the spatial patterns and interactions of female black bears (Moyer et al. 2006). Although genetic relatedness was not known in this study, it may explain the spatial attraction between this potential mother-daughter pair.

As expected during the breeding season, three of six females that exhibited significant interactions were spatially attracted to the home range overlap area they shared with one of the male bears in the study area. Since female black bears become sexually reproductive between two and seven years of age (Pelton 2003), all three bears were potentially estrous females, and it has been suggested that females will compete for the services of males (Barber and Lindzey 1986).

The only instance of temporal avoidance occurred between two females of the same age. Bunnell and Tait (1981) suggested that adult females may distance themselves from one another during the breeding season to decrease the likelihood of a dominant male preventing them from associating with other males. By separating themselves, the females may cause the male to monitor a larger area for competing males. This female mating strategy might explain the temporal avoidance between these two females.

Temporal avoidance might also be explained by a lack of social dominance.

Social dominance structures are typically influenced by age, gender, or size, but these two females were the same age and had a weight difference of only 7 kg. Therefore, the two females might be so closely matched as competitors for the same resources (i.e., food, shelter, mates) that the most cost effective option to maintain availability to those resources is through temporal avoidance.

The overall lack of significant spatial and temporal interactions suggest that current management practices based on black bear spatial patterns may need to be revised for coastal California black bear populations with high densities. Based on current telemetry and tracking technology, black bear spatial patterns may not be a useful tool for designing management strategies for the Little River study area or areas with similar bear densities and topographic characteristics. For example, one management strategy based on current practices is the use of internal population control methods. If large male black bears limit recruitment of smaller bears to an area, then one management strategy to limit tree damage by smaller bears would be to place harvest restrictions on the take of large males. However, the lack of small scale spatial and temporal interactions in the Little

River study area would suggest that dominance structures are only occurring at a much finer scale within food patches. Therefore, harvest restrictions for large males would not be an effective management strategy for reducing black bear tree damage in the Little

River study area. Although I was unable to track large males during this study, it is likely that, given the high levels of overlap and high black bear densities, large males are interacting similarly to the collared portion of the population.

Supplemental feeding is another management strategy currently practiced in the

Pacific Northwest that would not be effective in the Little River study area. Aside from the obvious financial costs of providing food supplements to an area with high black bear densities, managers would be unable to use the spatial and temporal interactions to predict potential changes in black bear spatial patterns in response to supplemental feeding. For example, managers would be unable to predict potential changes in home

33 range size or configuration around feeding stations. Also, females with cubs have been known to stop using feeding stations to avoid antagonistic encounters with other bears

(Fersterer et al. 2001). Since social dominance structures (i.e. avoidance and attraction) are likely occurring within food patches, certain age and gender classes might avoid feeding stations or be excluded from feeding stations by other bears.

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APPENDICIES

Appendix A. Sex, weight, and age for collared bears (n=16) in the Little River study area in northwestern California, 2007-2008.

Bear Sex Weight (kg) Agea

3 Female 77 5

4 Male 122 5

5 Male 102 -

6 Male 73 3

7 Male 100 5

9 Female 57 -

11 Male 61 4

15 Female 54 4

20 Female 61 4

45 Female 48 2

49 Female 75 4

50 Male 84 3

52 Female 73 6

67 Male 82 -

69 Female 50 3

71 Male 86 3

Mean 75 4 a - indicates age not determined.

Appendix B. Bootstrap analysis for 8 female and 8 male black bears in the Little River study area in northwestern California, 2008. Curved line represents minimum number of telemetry locations to obtain an accurate home range size.