Predatory and Foraging Behaviour of Brown Hyenas (Parahyaena brunnea (Thunberg, 1820)) at Cape Fur Seal (Arctocephalus pusillus pusillus Schreber, 1776) Colonies by Ingrid Wiesel Dissertation submitted in partial fulfilment of the requirements to obtain the title of a Doctorate of Natural Sciences at the Bio-centre Grindel and Zoological Museum, University of Hamburg, Germany June 2006 Supervisors: Prof. Dr. Harald Schliemann Biozentrum Grindel und Zoologisches Museum Universität Hamburg Martin-Luther-King-Platz 3 20146 Hamburg Germany Prof. Dr. Jörg Ganzhorn Biozentrum Grindel und Zoologisches Museum Universität Hamburg Martin-Luther-King-Platz 3 20146 Hamburg Germany Native speaker Dr. James D. Roth Department of Biology University of Central Florida 4000 Central Florida Blvd Orlando, Florida 32816-2368 USA Title drawing: Dr. Jean-Paul Roux To Dollar “When you have assembled what you call your ‘facts’ in logical order, it is like an oil-lamp you have fashioned, filled, and trimmed; but which will shed no illumination unless first you light it.” (Saint-Exupéry, The Wisdom of the Sands) Table of Contents Table of Contents CHAPTER 1 1 Introduction 1 CHAPTER 2 3 Study Areas and Study Period 3 2.1 Wolf Bay seal colony 4 2.2 Van Reenen Bay seal colony 5 2.3 Baker’s Bay seal colony 6 2.4 Study period 6 CHAPTER 3 8 Study Animals 8 3.1 Brown hyena (Parahyaena brunnea) 8 3.2 Cape fur seal (Arctocephalus pusillus pusillus) 10 3.3 Black-backed jackal (Canis mesomelas) 12 CHAPTER 4 15 Variability in the Availability of Cape Fur Seal Pups to Foraging Brown Hyenas Along the Southern Coastal Namib Desert 15 4.1 Introduction 15 4.2 Material and Methods 17 4.2.1 Biology of the study animal 17 4.2.2 Study area and study period 19 4.2.3 Determination of pup production 19 4.2.4 Seal pup growth, sex ratio and pup availability 20 4.2.5 Non-violent mortality 20 4.2.6 Seal pup carcass availability along beaches 22 4.2.7 Mortality factors 22 4.2.8 Anti-predator behaviour of seals 23 4.2.9 Data collection and statistics 24 4.3 Results 25 4.3.1 Pup production at mainland Cape fur seal colonies 25 4.3.2 Seal pup growth 26 4.3.3 Pup availability and sex ratio 28 4.3.4 Non-violent mortality 30 4.3.5 Anti-predator behaviour of seals 35 4.4 Discussion 36 4.4.1 Prey availability 36 4.4.2 Condition of prey 41 4.4.3 Anti-predator strategies of Cape fur seals 45 4.5 Summary 51 CHAPTER 5 52 The Importance of Coastal Resource Availability and Resource Distribution for Brown Hyena Abundance, Activity, Movement and Energy Budget 52 5.1 Introduction 52 5.2 Material and Methods 55 i Table of Contents 5.2.1 Immobilisation of hyenas 55 5.2.2 Assessment of the importance of the coast and the seal colonies 55 5.2.3 Brown hyena activity pattern and field metabolic rate 57 5.2.4 Brown hyena abundance around mainland seal colonies 58 5.2.5 Brown hyena density 59 5.3 Results 59 5.3.1 Assessment of the importance of the coast and the seal colonies 59 5.3.2 Brown hyena activity pattern and field metabolic rate 63 5.3.3 Brown hyena abundance 65 5.3.4 Brown hyena density 65 5.4 Discussion 66 5.4.1 Brown hyena abundance and density 66 5.4.2 Brown hyena home range size, activity and habitat use 69 5.4.3 Brown hyena movement and field metabolic rate 74 5.5 Summary 76 CHAPTER 6 77 Brown Hyena Foraging and Hunting Behaviour at Mainland Cape Fur Seal Breeding Colonies 77 6.1 Introduction 77 6.2 Material and Methods 80 6.2.1 Study area and study period 80 6.2.2 Brown hyena attendance at the Van Reenen Bay seal colony 80 6.2.3 Brown hyena foraging behaviour 81 6.2.4 Foraging and hunting behaviour 83 6.2.5 Prey encounter times 84 6.2.6 Efficiency and capture rate 84 6.2.7 Predation rate at seal colonies 84 6.2.8 Mass kill events 85 6.3 Results 86 6.3.1 Attendance of brown hyenas at the Van Reenen Bay seal colony 86 6.3.2 Brown hyena foraging behaviours 87 6.3.3 Brown hyena foraging behaviour at the Van Reenen Bay seal colony 89 6.3.4 Prey encounter times, hunting efficiency, and capture rate 94 6.3.5 Seal pup predation 96 6.3.6 Mass kill events 99 6.4 Discussion 100 6.4.1 Brown hyena foraging behaviour 100 a) Search for prey 100 b) Brown hyena hunting technique 102 c) Brown hyena hunting behaviour and handling of prey at seal colonies 104 d) Brown hyena hunting efficiency 107 e) Time budget 109 6.4.2 Predation rate at seal colonies 112 6.4.3 Mass kill events 115 6.5 Summary 118 ii Table of Contents CHAPTER 7 120 The Influence of Size, Sex and Age of Seal Pups on Brown Hyena Feeding Preferences 120 7.1 Introduction 120 7.2 Material and Methods 122 7.2.1 Study area and study period 122 7.2.2 Number of scavenged pups and kills 122 7.2.3 Mass of seal pups 123 7.2.4 Sex ratio and age of pups 124 7.2.5 Prey choice regarding the consumption of killed pups 125 7.3 Results 126 7.3.1 Prey choice regarding scavenged pups and kills 126 a) Van Reenen Bay seal colony 126 b) Wolf Bay seal colony 127 7.3.2 Prey choice regarding the condition of pups 128 7.3.3 Prey choice regarding sex of the pups 132 7.3.4 Prey choice regarding the age of the pups 132 7.3.5 Prey choice regarding the consumption of killed pups 134 7.4 Discussion 138 7.4.1 Capture of seal pups 138 a) To kill or to scavenge? 138 b) Condition of seal pups 140 c) Prey choice regarding the sex of the pup 141 d) Prey choice regarding the age of the pup 142 e) Summary 143 7.4.2 Consumption of kills 143 7.5 Summary 145 CHAPTER 8 146 Consumption of Seal Pups and Factors Influencing the Feeding Time and Energy Budget of Brown Hyenas 146 8.1 Introduction 146 8.2 Material and Methods 148 8.2.1 Study area and study period 148 8.2.2 Consumption of kills and scavenged pups 148 8.2.3 Feeding and handling time 149 8.2.4 Competition with black-backed jackals 149 a) Daily attendance pattern of jackals and predation rate 149 b) Interspecific competition 150 8.2.5 Removal or caching of seal pups 150 8.2.6 Prey choice regarding caches 151 8.2.7 Caloric value of brain tissue 151 8.3 Results 151 8.3.1 Consumption of prey 151 a) Consumption of kills 151 b) Consumption of scavenged pups 156 8.3.2 Feeding and handling time 157 8.3.3 Competition with black-backed jackals 159 iii Table of Contents a) Attendance of black-backed jackals at the Van Reenen Bay seal colony 159 b) Seal pup predation 160 c) Interspecific competition 161 8.3.4 Removal or caching of prey 162 8.3.5 Prey choice regarding caches 163 a) Kill versus scavenged pup 163 b) Surplus kills versus excessive kills 163 c) Mass of cached predations 164 d) Mass of cached non-violent mortalities 166 8.3.6 Value of brain tissue 166 8.4 Discussion 167 8.4.1 Consumption of prey 167 a)Consumption of kills 167 b)Consumption of scavenged pups 170 8.4.2 Feeding and handling time 171 8.4.3 Competition with black-backed jackals 172 8.4.4 Removal or caching of prey 175 8.4.5 Prey choice regarding caches 176 8.4.6 Value of brain tissue 177 8.5 Summary 179 CHAPTER 9 180 Conclusions 180 ACKNOWLEDGEMENTS 182 REFERENCES 184 APPENDIX 202 iv Chapter 1 Chapter 1 Introduction Many carnivore studies investigate predator-prey systems mostly within terrestrial or marine ecosystems (Kruuk 1972a, Schaller 1972, David 1987). Within these systems, carnivores usually use a wide variety of prey species with preferences for certain species (Kruuk 1972a, Schaller 1972). Carnivores usually prey on species on a lower trophic level within their ecosystem, but in coastal areas, where the terrestrial and marine ecosystems meet, marine mammalian carnivores may serve as a food source for their terrestrial equivalent (Stirling & McEwan 1975, Smith 1976, Stirling & Archibald 1977, Smith 1980, Andriashek et al. 1985). Such a predator-prey system is unusual and when in existence is usually highly seasonal, as marine mammals spend most of their time at sea or come ashore on islands where terrestrial carnivores do not occur (Burger & Gochfeld 1994). Exceptions are the Cape fur seal (Arctocephalus pusillus pusillus) breeding colonies that are found on the mainland along the Namibian and South African coast. Seals are ashore in these colonies all year round and serve as a permanent and concentrated food source for terrestrial carnivores such as brown hyenas (Parahyaena brunnea) and black-backed jackals (Canis mesomelas) (Oosthuizen et al. 1997, Wiesel 1998). Studies in these coastal areas have shown that the overall diet of these terrestrial carnivores mainly consists of Cape fur seals (Skinner & van Aarde 1981, Siegfried 1984, Stuart & Shaughnessy 1984, Stuart 1986, Skinner et al. 1995), with no seasonality in the use of this food source.