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 ECOLOGY OF SEABIRDS ON AILSA CRAIG, FIRTH OF CLYDE Ph D. Thesis BERNARD ZONFRILLO UNIVERSITY OF GLASGOW September 1997 ProQuest Number: 10391414 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 complete 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 10391414 Published by ProQuest LLO (2017). C o pyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code Microform Edition © ProQuest LLO. ProQuest LLO. 789 East Eisenhower Parkway P.Q. Box 1346 Ann Arbor, Ml 4 8 1 0 6 - 1346 GLASGOW uiïtftasriT UBKI 111 7 3 CO g u ^ s o w S ! S S r ^ UNIVERSITY o f GLASGOW DECLARATION I hereby declare that all the work within this Thesis is entirely of my own composition unless specifically stated. No part of this work has been offered or submitted for any other examination or degree. Signed Bernard Zonfrillo. 30 September 1997 SUMMARY The Focus of this thesis is the ecology of seabirds on Ailsa Craig, a remote, high, rocky island situated in the Firth of Clyde in south-west Scotland. The island is principally an internationally important Gann et colony but has locally significant numbers of other breeding seabirds. The status of seabirds on Ailsa Craig and in the Firth of Clyde in general, was examined. Possible reasons for the observed species fluctuations are examined. Selected aspects of the breeding ecology of seven seabird species on Ailsa Craig were studied. These are Fulmar, Gannet, Great Black-backed Gull, Herring Gull, Kittiwake, Guillemot and Razorbill. Diets of adult and young of most species are analysed and the growth rate of young is also examined in most cases from hatching to fledging. Growth rate is presented, in most instances, as both the absolute growth rate and the instantaneous growth rate, the latter being used for comparative purposes since it accounts for variation such as individual size, which may be a factor of sex or clinal variation. Dietary data and chick growth rates largely reflect food availability in the marine environment, and this is discussed with respect to the diet and foraging behaviour of the species Involved. Remote seabird islands are usually free of any naturally occurring mammalian predators but when alien mammals are transported to islands through anthropogenic agents the consequences for breeding seabirds can be disastrous. Burrow nesting species in particular can be seriously affected by fast- reproducing predators such as rats. Ailsa Craig was colonised by brown rats through shipwrecks around 1889. Following that time certain seabird species, all burrow nesters, gradually and completely died out. This was generally attributed to the effects of rat predation. The final section of this thesis describes a method whereby rats were eliminated from Ailsa Craig and details the techniques and monitoring methods involved. Following the commencement of rat eradication in 1991, preliminary results indicated increased biodiversity and increases in productivity of some bird species. Other important fauna and flora of the island also increased in the absence of rats. After monitoring for six years, the eradication of rats on Ailsa Craig appears to have been completely successful. in Jüùa Crai^Jhm t/USout/u Photo. S. Murray, August 1995 Sonnet on SiUsa Ü(pc^ chou eruggif ocemn ! Qive Answer from chff voice che ses fowls screnms ! %/$/%en were ch) shoulders mnncled in huge screams ? from che sun was chg broad forehead hid ? ^ow long is c since che ^VD^dhcg ^ow er bid %hee heave Co airg sleep from fachom dreams ? ^leep/ in che lap of chunder or sunbeams, (^ r when greg clouds are chg cold coverlid ? %hou answ er sc noc, for chou arc dead asleep ! %hg life is hue cwo dead ecemicies - %he lasc in air, che former in che deep ^ irsc wich che whales, lasc in che eagle skies - .fr o w n 'd w asc chou cil an earch()uake made chee sceep, ^^nocher cannoc wake chg gianc si%e. JàÆ/t J>!ÿrs/ure, JunelSlA lY [nilex iniilE ECOLOGY OF SIEABXRDS ON AELSA CRAXG, IFXRTH OF CJLYDIE- Title Page i Declaration Page ii Sum mary Page iii Frontispiece - .'///.sr/Or/?gy/rw; tita south. Page iv Index Pages 1-4 Introduction Introduction Pages 5 - 1 2 Sc ah inis 5 Threats to seabirds 7 Seabird studies 9 Focus o f this study 9 Rel'erences 11 Chapter L Seabird Populations of Ailsa Craig and The Firth of Clyde pages 13-36 1. I. Introduction 13 1, 2. Ailsa Craig 14 1. 3. Methods 15 i.4. Results 16 I. 4. 1. Population changes 17 L 5. Discussion 19 1.6. References 25 Figures 1. 1. - 1. 11. 2 6 - 3 6 Chapter 2. T h e Fulmar Fulmarus glacialis in the Firth of Clyde, breeding pages 37-68 success, diet and growth of chicks on Ailsa Craig, and the effects on predatory Brown Rats Rattus norvégiens. 2. I. Introduction 37 2. 1. 1. Fulmars in the North Atlantic. 37 2. 1. 2. The Fulmar colonisation o f Scotland 38 2. 1. 3. Colonisation o f the Clyde Area by Fulmars 39 2. 1. 4. Colony location and number o f apparently 39 occupied breeding sites 2. 2. Fulmars on Ailsa Craig 43 2. 2. 1. Breeding failure 43 2. 3. Investigation into the hreeding failure of Fulmars on Ailsa Craig 44 2. 3. 1. M ethods 45 2. 4. Results 46 2. 4. 1. Breeding Success 46 2. 4. 2. Growth o f Young 47 2. 4. 3. Diet 48 2. 5. Discussion 51 2. 6, References. 56 Figures 2. 1 .- 2 . 10. 59-68 Index Chapter. 3 Diet, growth, breeding success and migration of Gannets Morns pages 69 -99 hassanns on Ailsa Craig 3. 1. Introduction 69 3, 2. Methods 70 3. 3. Results 72 3. 3. L Die! 72 3. 3. 2. Growth 73 3. 3. 3. Breeding success 75 3. 3. 4. Dispersal and migration 75 3. 4. Discussion 76 3. 5. Relerences 82 Figures 3. 1 .-3 . 17. 83-99 Chapter 4. Diets of adult and chick Herring Gulls Laras argentatus pages 100-114 argenteus on Ailsa Craig, south-west Scotland 4. 1. Introduction 100 4. 2. Methods 100 4. 3. Results 102 4. 4. Discussion 105 4. 5. References 110 Figures 4. I. - 4. 2. 113 - 114 Chapter 5. Great Black-backed Gull Larus marimis diet, chick growth and pages 115-136 feeding ecology on Ailsa Craig. 5. 1. Introduction 115 5. 2. Clyde populations 115 5. 3. Methods 116 5. 4. Identification of eggs and young gulls 117 5. 5. Results 118 5. 5. 1. Diet 118 5. 5. 2. Breeding success 120 5. 5, 3. Growth 121 5, 5. 4. Dispersal 122 5. 6. Discussion 122 5. 7. References 127 Figures 5. 1. - 5. 9. 128 - 136 Index Chapter 6. Kittiwake Rissa tridactyla., on Ailsa Craig - aspects of pages 137-162 breeding success, feeding ecology, and chick growth. 6. 1. Introduction 137 6. 2. Methods 138 6. 3. Results 140 6. 3. 1. Amiual cycle o f Kitthvakes on Ailsa Craig 140 6. 4. Breeding success 141 6. 5. Chick feeding and growth 143 6. 5. 1. Chick provisioning 143 6. 5. 2. Chick growth 144 ;ïï. 6. 6. Pre-hreeding diet of adult Kittiwakes 145 6. 7. Discussion 146 6. 8. References 155 Figures 6. 1 .- 6 . 4. 159 - 162 Chapter 7. Guillemots Uria aalge alhumis on Ailsa Craig - aspects of pages 163-175 breeding biology, diet, chick growth and population trends, 7. 1, Introduction 163 7. 2. Annual cycles of Auks on Ailsa Craig. 164 7. 3. Auk nuinhers in the Clyde. 165 7. 4. Methods 165 7. 4. 1. Giiilleniot data collection 165 7. 4, 2. D iet 166 7. 5. Results 166 7. 5. 1. Fledglings 166 7. 5. 2. D iet 167 7. 6. Discussion 168 7. 7. References 173 Figure 7. 1. 175 Chapter 8. Colonisation, ecology and eradication of the Brown Rat pages 176 - 206 Rattus norvégiens on Ailsa Craig. 8. I. Introduction 176 8. 1. 1. Historical perspective 176 8. 1. 2. Summary o f rat behaviour and ecology 177 8. 1.3. Rats as seabird predators 177 8. 1. 4. Colonisation of Ailsa Craig and predation 178 o f seabirds by rats 8 .1 . 5. Early attempts to control rats 180 Index 8. 1. 6. Rats and seabird interactions on Ailsa Craig and 181 elsewhei^e in the Firth o f Clyde 8. 1. 7. Evidence o f Rat Predation 181 8. 2. Methods 183 8. 2. 1. Pilot Studies 183 8.