At Point Reyes National Seashore, California By
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Spatial Ecology and Population Dynamics of Tule Elk ( Cervus elaphus nannodes ) at Point Reyes National Seashore, California by McCrea Andrew Cobb A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Environmental Science, Policy and Management in the GRADUATE DIVISION of the UNIVERSITY OF CALIFORNIA, BERKELEY Committee in charge: Professor Reginald H. Barrett, Chair Professor Justin S. Brashares Professor Maggi Kelly Professor Eileen A. Lacey Spring 2010 1 Spatial Ecology and Population Dynamics of Tule Elk ( Cervus elaphus nannodes) at Point Reyes National Seashore, California © 2010 by McCrea Andrew Cobb 2 Abstract Spatial Ecology and Population Dynamics of tule elk ( Cervus elaphus nannodes ) at Point Reyes National Seashore, California by McCrea Andrew Cobb Doctor of Philosophy in Environmental Science, Policy and Management University of California, Berkeley Professor Reginald H. Barrett, Chair The tule elk ( Cervus elaphus nannodes ) was reintroduced to Point Reyes National Seashore, California in 1978. After exhibiting irruptive growth for 20 years, elk abundances have fluctuated. Three subpopulations of elk currently inhabit Pt. Reyes: a fenced subpopulation at high density; a free-ranging subpopulation in designated wilderness at low density; and a free- ranging subpopulation on active ranchland at low density. Little is known about the spatial ecology and population dynamics of tule elk. This unusual situation provided an opportunity to quantify and compare factors affecting the home ranges, group sizes, resource selection, small- scale movements and population dynamics of tule elk. I collected biweekly fixes on radio- collared elk cows between 2005 and 2008 to examine herd structures, space use patterns, grouping behavior and survival rates of tule elk. Radio-telemetry data revealed 6 herds of elk at Pt. Reyes (4 at Tomales), which had distinct herd ranges and showed little spatial interaction. Fixed kernel home ranges were some of the smallest for elk in North America (217 ha, SE = 35), and were negatively correlated with elk density. Home range sizes were 300% smaller than previous estimated for elk at Pt. Reyes in 1998. The sizes of elk groups peaked during the winter and mid-summer, and were smallest during the spring parturition and fall rutting periods. Elk with larger home range sizes generally formed smaller groups. Resource selection function (RSF) results indicated that tule elk at Pt. Reyes selected flat, grassland-dominated habitats over hilly, scrub and forest habitats; although resource selection patterns varied among herds. Elk shifted to lower elevations, steeper slopes and more scrub-dominated habitats during the dry season (May – October). Most elk showed an aversion to areas close to roads and trails, but this result was not consistent across all herds. I quantified small-scale movement patterns of tule elk using hourly fixes from GPS-collared elk. Elk exhibited daily cycles in their movement patterns by increased their hourly movements in the morning and evening hours. Elk daily movements were longest during wet spring months and shortest during the dry fall months. Elk slowed when traveling through homogeneous grassland habitat. Windy conditions caused elk to slow, but precipitation had no effect on elk movement. Elk moved faster when closer to roads and trails. Elk in higher density herds moved slower on an hourly scale than lower density herds, but herd density had no affect on daily movement patterns. Using known-fate models applied to radio- telemetry data, I estimated annual cow elk survival was 0.96 (SE = 0.02). I captured and 1 monitored radio-collared elk calves from 2005 to 2007 to estimate calf survival and causes of mortality. Using known-fate models, I estimated annual survival for elk calves was 0.81 (SE = 0.02). The primary cause of death for both cows and calves was starvation, which was often accompanied by copper and selenium deficiencies. Sensitivity and elasticity estimates of elk vital rates revealed that adult cow elk survival contributed the most (30%) to elk annual population change ( λ). The D Ranch and Limantour herds were expected irruptive growth and by 2018 increase to 393 and 389 elk, respectively, based on stochastic population projection models. The projected future abundance of elk in the Tomales herds was dependant on the previous year’s annual rainfall: models projected increases in elk abundance following years of above-average rainfall but no change in elk abundance following years of below-average rainfall. Future growth of the D Ranch and Limantour elk herds will likely concentrate on adjacent ranchlands, given RSF models results, and will likely result in future conflicts between NPS management, unless proactive actions are taken. 2 TABLE OF CONTENTS Table of Contents…………………………………………………………………………………..i List of Tables…………………………………………………………………………...................ii List of Figures…………………………………………………………………………………….vi Acknowledgements……………………………………………………………………………….xi Introduction………………………………………………………………………………………..1 Chapter 1. Herd Stability, Grouping Behavior and Home Range Sizes of Tule Elk at Point Reyes National Seashore…………………..............……………..…19 Chapter 2. Habitat Use and Resource Selection of Tule Elk at Point Reyes National Seashore………………………………………………..61 Chapter 3. Small-scale Movement Patterns of Tule Elk at Point Reyes National Seashore………………………………………………..97 Chapter 4. Population Dynamics of Tule Elk at Point Reyes National Seashore………………………………………………………………138 Appendix Tule Elk Resource Selection Model Results by Herd…..………………………198 i LIST OF TABLES Chapter 1 Table 1. Summary of radio-collared elk data……………………………….…………...33 Table 2. Coefficients of association among radio-collared elk in the D Ranch herd…………………………………………….………………………….….......34 Table 3. Coefficients of association among radio-collared elk in the Limantour herd……………………………….…………………………..…….………...35 Table 4. Coefficients of association among radio-collared elk in the Tomales Point Elk Reserve herds………………….…………….…..………….……….36 Table 5. Average annual herd range sizes………………………………………………38 Table 6. Estimated annual herd size, available grassland, and herd density by herd……………….………………………………………………………..…………39 Table 7. Average group sizes and age / sex classifications by herd and study year………………….…………………………………………..…………………43 Table 8. Average group sizes and age / sex classifications by season and herd………………………….…………………………………………..……………….45 Table 9. Home range and core area sizes by study year………………………………...52 Table 10. Results of linear regression analyses of annual home range sizes against herd density………………….…………………………………………………...56 Table 11. Results of linear regression analyses of annual home range sizes against average annual group sizes……………………………………………………....58 Table 12. Results of linear regression analyses of annual herd density against average annual group sizes……………………………………………………....60 Chapter 2 Table 1. Summary of radio-telemetry data by herd…………………………………….82 Table 2. Composition of used and available habitats …………………………………..84 Table 3. Comparison of elk habitat use during wet and dry seasons…………………....86 ii Table 4. Kruskal-Wallis chi-square tests for significant differences between used and available habitat types…………….………………………………….87 Table 5. Population-level resource selection function (RSF) coefficient estimates………………………………………………...………………………………..88 Table 6. Herd-level and population-level resource selection function (RSF) models……………………………………………………………………….............…...90 Table 7. Distribution of habitat coefficients in herd-level and population- level resource selection function (RSF) models…………..……………………………..91 Table 8. Assessment of resource selection function (RSF) models by herd and population…………..……………………………………………………..……92 Chapter 3 Table 1. Summary of predictor coefficients in candidate model set for quantifying hourly and daily step lengths….…………………………………………...115 Table 2. Summary of GPS-collar data……………….………………………………...116 Table 3. Spearman rank-order correlation coefficients of predictor variables used in modeling hourly and daily step lengths……………………………...122 Table 4. List of candidate models quantifying hourly step lengths……………………123 Table 5. Summary of most parsimonious model for quantifying hourly step lengths……………………………………………………………………….……..124 Table 6. List of candidate models quantifying daily step lengths……………………...132 Table 7. Summary of the most parsimonious model for quantifying daily step lengths……………………………………………………………………………...133 Chapter 4 Table 1. Predictor variables in candidate known-fate models quantifying monthly and annual survival of cows and calves……………….………………………158 Table 2. Results of linear regression analyses examining the relationship of annual precipitation, calf: cow ratios and annual rate of population change)………… ………………………………………………………..……………..163 Table 3. Average age at capture and fate of radio-collared cows by herd……………..165 iii Table 4. Causes of cow mortalities……………………………………….…………....166 Table 5. Sex and fate of radio-collared calves by herd....................…………………...168 Table 6. Causes of calf mortalities……………………………………………………..169 Table 7. Candidate linear regression models quantifying capture weight of radio-collared calves……………………………………………………………………172 Table 8. Results of the most parsimonious linear regression model quantifying birth weight of radio-collared calves………………………………………173 Table 9. Estimated annual survival of cows by herd and year………………………....175 Table