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https://theses.gla.ac.uk/ Theses Digitisation: https://www.gla.ac.uk/myglasgow/research/enlighten/theses/digitisation/ This is a digitised version of the original print thesis. Copyright and moral rights for this work are retained by the author A copy can be downloaded for personal non-commercial research or study, without prior permission or charge This work cannot be reproduced or quoted extensively from without first obtaining permission in writing from the author The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the author When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given Enlighten: Theses https://theses.gla.ac.uk/ [email protected] THE USE OF SPIDER SILK IN THE NESTS OF SMALL BIRDS, WITH PARTICULAR REFERENCE TO THE CHAFFINCH (FRINGILLA COELEBS). A thesis submitted to the Faculty of Science, University of Glasgow, for the degree of Master of Science by Nicholas P Storer May 1991 ProQuest Number: 11011423 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a com plete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQuest 11011423 Published by ProQuest LLC(2018). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States C ode Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 CQN1EN15. SUMMARY. CHAPTER 1 . INTRODUCTION................................................... 1 CHAPTER 2. CHAFFINCH BREEDING BIOLOGY................................... 5 2.1) The structure of chaffinch nests.............................. 5 2.2) The construction of nests by chaffinches...................... 6 2.3) Chaffinch territories.......................................... 7 2.4) The timing of chaffinch breeding seasons...................... 7 2.4.1) Geographical variation in the timing of breeding....... 9 2.5) Time and energy budgets of chaffinches during the breeding season... 10 2.6) Reasons for nest abandonment by chaffinches.................. 11 2.7) The importance of the nest to breeding success............... 12 CHAPTER 3. SPIDERS AND THEIR SILK........................................ 14 3.1) Spider classification........................................... 14 3.2) Spider silk production......................................... 17 3.2.1) Silk glands and the different types of silk............ 18 3.2.2) The orb web - an example of different silks in one structure... 23 3.3) Amino-acid composition of silk............. 25 3.4) Physical properties of silk..................................... 28 3.4.1) Strength and extensibility of silk........ 28 3.4.1.1) Determinants of thread diameter................... 31 3.4.2) Adhesiveness of spider silk............................. 34 3.4.3) Summary of the properties of silk...................... 36 3.5) Silken structures.............................................. 36 3.5.1) The webs, retreats and cocoons of 7 important families 39 CHAPTER 4. INTRODUCTION TO INVESTIGATIONS OF CHAFFINCH NESTS AND SILK... 46 CHAPTER 5. MATERIALS AND METHODS......................... 48 5.1) Study site...................................................... 48 5.2) Timing of chaffinch breeding at Garscube Estate.............. 48 5.3) Investigation of chaffinch nests............................... 49 5.3.1) Sources used to obtain the nests........................ 49 5.3.2) Examination of the materials in each nest.............. 51 5.3.3) Silk content and use in the nests...................... 52 5.4) Silk identification............................................. 53 5.4.1) Characterisation of silk from spiders at Garscube Estate.... 53 5.4.2) Identification of unknown silk taken from nests....... 54 5.5) Silk availability............................................... 55 5.5.1) Year-round survey of webs, retreats and cocoons....... 55 5.5.1.1) Effect of time-of-day on silk count.............. 57 5.5.2) Investigation of the turnover of retreats and cocoons.... 57 CHAPTER 6. RESULTS......................................................... 58 6.1) Timing of chaffinch breeding at Garscube Estate.............. 58 6.2) Investigation of chaffinch nests.............................. 61 6.2.1) Nest dimensions.......................................... 61 6.2.2) Investigation of the materials in each nest............ 61 6.2.2. 1) Nests built by the same female.................... 62 6.2.2.2) Effects of timing of nest-building................ 63 6.2.3) The silk content of nests............................... 63 6.2.3.1) Distribution of silk through the nests........... 63 6.2.3.2) Effect of nest size upon number of silk units 64 6.2.3.3) Materials to which silk is attached.............. 64 6.2.3.4) Correlations between silk and other materials 65 6.2.3.5) Silk distribution between the materials.......... 66 6.2.3.6) Differences in the extent of the use of web and cocoon silk.... 66 6.2.3.7) Correlations of web and cocoon with lichen, wood and bark.... 66 6.2.3.8) Differences between web and cocoon in use in Layer B .... 67 6.2.3.9) Comparison of wool with silk....................... 67 6.3) Spider silk identification............................... 68 6.3.1) Characterisation of silk from Garscube spiders... 68 6.3.1. 1) The spider species whose silk was examined....... 68 6.3.1.2) Spider web characterisation....................... 68 6.3.1.3) Spider cocoon characterisation.................... 69 6.3.2) Examination of silk samples collected from nests...... 71 6.3.2.1) Web silk from nests................................ 71 6.3.2.2) Cocoon silk from nests............................. 71 6.4) Silk availability.............................................. 72 6.4.1) Spiders present at Garscube Estate..................... 72 6.4.2) Year-round survey of webs, retreats and cocoons....... 72 6.4.2.1) Combined results from all sites examined......... 72 6.4.2.2) Site-by-site breakdown............................. 74 6.4.2.3) Effect of time of day..................... 76 6.4.3) Turnover of cocoons and retreats.................. 77 CHAPTER 7. CHAFFINCH NEST STRUCTURE AND THE USE OF SILK............... 78 7.1) The nesting materials employed................................. 78 7.2) Silk as a chaffinch nesting material........................... 85 CHAPTER 8. IDENTIFICATION OF SILK UNITS FROM CHAFFINCH NESTS............. 93 8.1) Types of silk found............................................ 93 8.1.1) Types of web silk found................................. 93 8.1.2) Types of cocoon silk found.............................. 94 8.2) Problems with the method of identification.................... 96 CHAPTER 9. FACTORS AFFECTING CHOICE OF SILK BY CHAFFINCHES............. 98 9.1) Abundance of silk through the year............................ 98 9.1.1) Web silk changes through the year.................... 98 9 .1.1 .1) Orb webs.......................................... 98 9.1.1.2) Sheet webs........................................ 99 9.1.1.3) Irregular webs................................... 100 9.1.1.4) Cribellate webs.................................. 100 9.1.2) Cocoon and retreat number changes through the year 101 9.1.3) Comparability of successive web counts................. 102 9.1.4) Limitations of the data in representing the whole environment.... 103 9.2) Relative availability of silk types during the chaffinch breeding season.... 104 9.2.1) Web silk............................................... 104 9.2.2) Cocoon silk............................................ 106 9.3) Relative suitability of silk types during the chaffinch breeding season.... 107 9.3.1) Web silk............................................... 107 9.3.2) Cocoon silk............................................ 108 9.4) Summary of factors affecting chaffinch choice of silk....... 108 CHAPTER 10. EFFECT OF SILK USE UPON CHAFFINCH...... BEHAVIOUR............ 110 10.1) Effect upon the methods used in searching for nest materials 110 10.1.1) Web collection.......................................... 110 10.1.2) Cocoon collection....................................... Ill 10.2) Silk availability and the location of chaffinch territories 113 10.3) Silk availability and the timing of chaffinch nesting......... 114 CHAPTER 11. CONCLUSIONS 120 11.1) What makes spider silk such a widespread nesting material?... 120 11.2) How is silk used in the nests of chaffinches?........ 123 11.3) What types of silk are used by chaffinches?........... 124 11.4) Could silk availability limit the time or place of nesting? 125 11.5) Improvements and extensions to the method............. 126 11.5.1) Information on the nests examined...................... 126 11.5.2) Silk identification.................................... 127 11.5.3) Silk survey methods.................................... 129 11.5.4) Investigations into chaffinch behaviour................. 130 11.5.5) Summary................................................. 130 11.6) Wider implications of this study - other birds....... 130 11.7) Relationship between silk in nests and webs as a food source.... 134 REFERENCES.......................................................... 135 APPENDIX A. DETAILS