UNIVERSITY OF SOUTHAMPTON THE ECOLOGY OF THE SLOW-WORM (ANGUIS FRAGILIS L.) IN SOUTHERN ENGLAND. A Thesis submitted for the Degree of Master of Philosophy. Department of Biology, University of Southampton, NICHOLAS DANE SMITH 1990 TO JANE Slow-worm. The blind worm; a large viper, not mortal, scarcely venomous. Dr. Johnson (1785), A Dictionary of the English Language. If the adder could hear, and the blindworm see. Neither man nor beast would ere go free. Old rhyme, quoted by Skeat (1910), An Etymological Dictionary of the English Language, 4th Edition. all Double, double toil and trouble: Fire burn and cauldron bubble. 2nd witch Fillet of a fenny snake; In the cauldron, boil and bake; Eye of newt, and toe of frog. Wool of bat, and tongue of dog. Adder's fork and blind-worm's sting. Lizard's leg and howlet's wing. For a charm of powerful trouble Like a hell-broth boil and bubble. Macbeth IV, i 10-19. CONTENTS ABSTRACT X ACKNOWLEDGEMENTS xi CHAPTER 1. INTRODUCTION 1 1.1 ANGUIS FRAGILIS AND THE FAMILY ANGUIDAE 1 1.2 A BRIEF DESCRIPTION OF THE SLOW-WORM 2 1.3 DISTRIBUTION OF THE SLOW-WORM 5 1.4 DISTRIBUTION AND STATUS OF THE SLOW-WORM IN THE BRITISH ISLES 8 1.5 LITERATURE AND PREVIOUS WORK ON THE SLOW-WORM 11 1.6 AIMS OF THE PRESENT STUDY 12 CHAPTER 2. GENERAL METHODS 14 2.1 INTRODUCTION 14 2.2 STUDY SITES 14 2.3 FIELD METHODS 16 2.3.1 Searching and captures 16 2.3.2 Site visits 17 2.3.3 Data from finds of slow-worms 18 2.4 IDENTIFICATION OF INDIVIDUALS 20 2.4.1 Introduction 20 2.4.2 The photographic method 21 2.4.3 Advantages and disadvantages of photography 22 2.5 THE STUDY OF REPRODUCTION 23 2.6 STATISTICAL ANALYSIS 24 CHAPTER 3. CAPTURES AND MOVEMENTS 2 6 3.1 INTRODUCTION 2 6 3.2 ANALYSIS 27 3.2.1 The sex and size categories 27 3.2.2 Finds of slow-worms at each visit to a site 28 3.2.3 The dates of entering and leaving hibernation 28 3.2.4 Relationship of weather conditions to finds of slow-worms 29 IV 3.2.5 Analysis of the frequency of capture of individuals 30 3.2.6 Analysis of movements and ranges 30 3.2.7 Finds of other vertebrate species 33 3.3 RESULTS 33 3.3.1 Numbers of slow-worms found 33 3.3.2 Emergence from and retreat into hibernation 33 3.3.3 Monthly variation in the numbers of slow-worms found per visit 35 3.3.4 Relationship of weather conditions to finds of slow-worms 36 3.3.5 Frequencies of capture of individuals 37 3.3.6 Movements 38 3.3.7 Areas and ranges of movement 4 0 3.3.8 Finds of other vertebrate species 42 3.4 DISCUSSION 44 3.4.1 Numbers of slow-worm found per visit and weather 44 3.4.2 Hibernation in the slow-worm 44 3.4.4 Movements 4 6 CHAPTER 4. REPRODUCTION 4 8 4.1 INTRODUCTION 4 8 4.2 ANALYSIS OF DATA 50 4.2.1. Introduction 50 4.2.2 Date of mating 51 4.2.3 Date of birth 51 4.2.4 Frequency of reproduction 52 4.2.5 Size of litters 53 4.2.6 Size and weight of young at birth 53 4.2.7 The possible effects of tail loss by the mother on litter size and size of young 53 4.2.8 Size of litters related to size of female 53 4.2.9 Size and weight of young related to size of female 54 V 4.2.10 Total weight of litter related to size of female 54 4.2.11 Incidence of dead and deformed young 55 4.3 RESULTS 55 4.3.1 Date of mating 55 4.3.2 Date of birth 57 4.3.3 Frequency of reproduction 57 4.3.4 Size of litters 58 4.3.5 Size and weight of young at birth 58 4.3.6 The possible effects of tail loss by the mother on litter size and size of young 59 4.3.7 Size of litters related to size of female 60 4.3.8 Size and weight of young related to size of female 61 4.3.9 Total weight of litter related to size of female 61 4.3.10 Incidence of dead and deformed young 61 4.4 DISCUSSION 63 4.4.1 Comparison with older work on the slow- worm 63 4.4.2 Possible effects of the loss of the tail 63 4.4.3 The slow-worm and viviparity 65 4.4.4 Size of female and size of young 66 4.4.5 Incidence of dead and deformed young 67 4.4.6 The work of Patterson (1983) 69 CHAPTER 5. POPULATION ECOLOGY 72 5.1 INTRODUCTION 72 5.2 ANALYSIS 72 5.2.1 Introduction 72 5.2.2 Estimation of the total numbers of young born 74 5.2.3 The sex ratio 75 5.2.4 Size classes 75 5.2.5 Density estmates 76 5.3 RESULTS 7 6 VI 5.3.1 Total numbers of young born 7 6 5.3.2 The sex ratio 76 5.3.3 Size classes 77 5.3.4 Density estmates 78 5.4 DISCUSSION 78 CHAPTER 6 GROWTH 8 0 6.1 INTRODUCTION 8 0 6.2 METHODS AND ANALYSIS 80 6.2.1 Possible growth models 80 6.2.2 First year and older juveniles 82 6.2.3 Sub-adults and adults 83 6.2.4 Maximum size of adults 84 6.3 RESULTS 85 6.3.1 Growth from birth to the first hibernation 85 6.3.2 Growth in the first full season 85 6.3-. 3 Growth of sub-adults and adults 87 6.3.4 Maximum size of adults 88 6.4 DISCUSSION 89 CHAPTER 7. TEMPERATURE RELATIONS 91 7.1 INTRODUCTION 91 7.2 METHODS AND ANALYSIS 94 7.2.1 Field measurements 94 7.2.2 Measurement of the "maximum tolerated temperature" 95 7.2.3 Analysis 95 7.3 RESULTS 9 6 7.3.1 Differences between the sexes 96 7.3.2 Comparison of the two main sites. 97 7.3.3 Relationship between cloacal and air temperatures 98 7.3.4 Relationship between SVL and temperatures 98 7.3.5 Variation of temperatures with month 99 7.3.6 Variation of temperatures with hour 100 7.3.7 Variation of temperatures with cloud cover 100 Vll 7.3.8 Variation of temperatures with proportion of tin in sun 101 7.3.9 Variation of temperatures with whether animal in sun or not 101 7.3.10 Variation of temperatures with level of wind strength 102 7.3.11 "Maximum tolerated temperature" 102 7.4. DISCUSSION 103 7.4.1 Methods and results of the present study 103 7.4.2 Comparison of data with other species 105 CHAPTER 8 CLIMATE AND THE DISTRIBUTION OF THE SLOW-WORM 110 8.1 INTRODUCTION 110 8.2 DISTRIBUTION OF THE SLOW-WORM IN THE IBERIAN PENINSULA 111 8.3 CLIMATE STATIONS AND VARIABLES 112 8.4 ANALYSIS 114 8.5 RESULTS 116 8.6 DISCUSSION 118 CHAPTER 9 SOME MISCELLANEOUS CONSIDERATIONS 122 9.1 INTRODUCTION 122 9.2 WHAT DO SLOW-WORMS EAT? 122 9.3 WHAT EATS SLOW-WORMS? 123 9.4 THE PATTERN AND COLORATION OF SLOW-WORMS 125 REFERENCES APPENDIX Vlll UNIVERSITY OF SOUTHAMPTON ABSTRACT FACULTY OF SCIENCE DEPARTMENT OF BIOLOGY Master of Philosophy THE ECOLOGY OF THE SLOW-WORM (ANGUIS FRAGILIS L.) IN SOUTHERN ENGLAND by Nicholas Dane Smith The slow-worm, Anguis fraqilis, is a legless lizard in the family Anguidae. The ecology of the species was studied by weekly visits to two sites on the Isle of Purbeck, Dorset, England from 1981 to 1988. Other sites were visited less often. Animals were found under pieces of corrugated iron sheet that had been placed on the ground. Adults were photographed and identified on recapture by the pattern on the underside of the head. Pregnant females were retained in captivity until the birth of the young. A total of 3456 slow-worms were found. Capture rates of known individuals were low, often less than once a year. There were differences in rate of captures of four sex and size class over the season. Males predominated in spring, females were found most often in summer and sub-adults and juveniles were commonest in autumn. Rates of movement were low. There was no evidence of territory formation. Mating was only observed once. Females with sperm in the cloaca were found in May. The litters of 1 to 18 (average 8) were born in late summer. Larger females had larger litters but not larger young. In 1986, litter sizes were small with many of the young deformed. The sex ratios were not equal. The bias was to females at one site and to males at the other. Cloacal temperatures, low for a temperate reptile, ranged from 9.8 to 33.2 "C, with a median of 24.9 °C. There was little evidence of precise thermoregulation. Cloacal temperatures were highest in summer on sunny days, but varied little with time of day. The distribution in the Iberian peninsula was shown by discriminant function analysis to be correlated with cooler, wetter climates. IX ACKNOWLEDGEMENTS Many people contributed in large and small ways to this work.