n Cross, Adam D. P. (2014) The influence of seabird-derived nutrients on island food-webs. PhD thesis. http://theses.gla.ac.uk/6312/ Copyright and moral rights for this thesis are retained by the author A copy can be downloaded for personal non-commercial research or study, without prior permission or charge This thesis 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 Glasgow Theses Service http://theses.gla.ac.uk/ [email protected] The influence of seabird-derived nutrients on island food-webs Adam D. P. Cross Submitted in fulfilment of the requirements for the Degree of Doctor of Philosophy Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences University of Glasgow September 2014 Declaration I declare that the work described in this thesis is of my own composition and has been carried out entirely by myself unless otherwise cited or acknowledged. No part of this thesis has been submitted for any other degree or qualification. The following chapter has been published in co-authorship with my supervisor and others: Chapter 6: published as Cross, A. D. P., Hentati-Sundberg, J., Osterblom, H., McGill, R. A. R. and Furness, R. W., 2014. Isotopic analysis of island House Martins Delichon urbica indicates marine provenance of nutrients. Ibis, 156, 676 – 681. Adam Cross Glasgow 2014 Abstract There is an increasing understanding of the influence seabirds have on island food webs globally, which often arises from the trans-boundary input of nutrients. Seabird-derived nutrients, primarily in the form of guano, can have significant effects on island communities by increasing primary productivity and then indirectly influencing other species. However, there are few studies looking at how the influence of seabirds permeates island food webs to higher trophic levels, in particular within the United Kingdom, which holds globally significant populations of seabirds. To understand the extent to which seabirds influence islands, the size of the seabird population must be first reliably determined. With an increasing seabird population size and density the effects of seabirds on land increases concomitantly. The Atlantic puffin Fratercula arctica is a difficult species to reliably monitor, given its underground presence from the use of burrows and its notoriously erratic attendance at colonies. This study looks firstly at a novel method to monitor the Atlantic puffin using time-lapse photography. Time-lapse photography provides a way to derive an estimate of population size from counts of individuals, by repeated photographs across a period of time with relatively low cost and from areas normally considered inaccessible. The results showed there was a significant and positive relationship between the maximum numbers of Atlantic puffins observed and the size of the population; further work is required though to reduce the error associated with population size estimates. Data from high temporal resolution time-lapse photography shows how the attendance of Atlantic puffins at the colony varies over different temporal scales. Given the variability in sampling intensity the study stresses the need for standardised sampling intensity with the use of photography to monitor Atlantic puffins. Secondly, this study showed how the presence of two seabird species, the Atlantic puffin and the great skua Stercorarius skua, alters island food webs. These seabird species are likely to change plant community diversity, relative to areas without seabirds. The chemical concentration of grasses inside seabird colonies was also altered: grasses had significantly higher concentrations of nitrogen and also had higher values of δ15N, relative to areas without seabirds. These chemical alterations suggest that nutrients from seabirds are incorporated into local vegetation. Furthermore, samples of hair from rabbits and sheep found within puffin colonies also had significantly higher values of δ15N, suggesting that nutrients travel from seabirds into secondary consumers, via ornithogenic forage. An 2 additional study on the transfer of nutrients within island food webs showed how ornithogenic nutrients deposited on an island in the Baltic Sea were incorporated into house martins, via aquatic insects. These studies, along with an understanding of seabird population size, suggest that the impact of seabirds on island food webs may be considerable and have large consequences for island conservation and management. 3 Table of Contents Acknowledgements ................................................................................................................ 8 Introduction .......................................................................................................................... 10 Chapter 2 - Variation in Atlantic puffin Fratercula arctica colony attendance; monitoring using time-lapse photography. .................................................................................... 23 2.1 Introduction ........................................................................................................... 25 2.2 Methods ................................................................................................................. 28 2.3 Results ................................................................................................................... 38 2.4 Discussion ............................................................................................................. 54 Chapter 3 - Monitoring Atlantic puffins Fratercula arctica using time-lapse photography . 62 3.1 Introduction ........................................................................................................... 64 3.2 Methods ................................................................................................................. 67 3.3 Results ................................................................................................................... 73 3.4 Discussion ............................................................................................................. 84 Chapter 4 - A bioenergetic model estimating the nutrient input from Atlantic puffins Fratercula arctica and great skuas Stercorarius skua onto Mingulay ........................ 93 4.1 Introduction ........................................................................................................... 95 4.2 Methods ................................................................................................................. 98 4.3 Results ................................................................................................................. 107 4.4 Discussion ........................................................................................................... 112 Chapter 5 - The influence of Atlantic puffins Fratercula arctica and great skuas Stercorarius skua on Scottish islands ....................................................................... 123 5.1 Introduction ......................................................................................................... 125 5.2 Methods ............................................................................................................... 129 5.3 Results ................................................................................................................. 142 5.4 Discussion ........................................................................................................... 154 Chapter 6 - Isotopic analysis of island House Martins Delichon urbica indicates marine provenance of nutrients............................................................................................. 163 6.1 Introduction ......................................................................................................... 165 6.2 Methods ............................................................................................................... 167 4 6.3 Results ................................................................................................................. 169 6.4 Discussion ........................................................................................................... 172 Chapter 7 – General Discussion... ...................................................................................... 176 APPENDIX I ...................................................................................................................... 181 APPENDIX II .................................................................................................................... 185 APPENDIX III ................................................................................................................... 188 List of References .............................................................................................................. 195 5 List of Tables Table 2.1. Summary statistics of the photographs and number of puffins in photographs for each colony........................................................................................................................... 43 Table 2.2. Model coefficients for the analysis of the effect of breeding stage, daily period and colony on