Breeding Ecology of Arctic Tern (Sterna paradisaea) and Common Tern (Sterna hirundo) Laura Claire Morris Submitted in accordance with the requirements for the degree of Doctor of Philosophy University of Newcastle upon Tyne School of Agriculture, Science and Engineering 20 February 2013 All illustrations and photographs are by Laura C Morris Acknowledgements I should like to thank Dr Richard Bevan and Dr Chris Redfern, for first hiring me as a research assistant and then supporting my application for a Ph.D. I am incredibly grateful for their generous offering of advice, encouragement, support and time. I am grateful to the Royal Society for the Protection of Birds for permission to work on Coquet Island. In particular I should like to thank Dr Paul Morrison, who provided invaluable logistical support in the field and made sure any spare time was enjoyed to the full. I should also like to thank Sarah Lowe, without whose help I would have been completely lost in my first season, Zoe Tapping for laughter and help during my second, third and fourth seasons, and Wesley Davis for making my last field season such a special one. Finally I should like to thank my family and friends for their unfailing support, comfort and laughter which have made these years as enjoyable as they have been. i Breeding Ecology of the Arctic Tern (Sterna paradisaea) and Common Tern (Sterna hirundo) Laura Claire Morris Ph.D thesis, May 2012 Abstract Seabird breeding populations have been experiencing change over the last 40 years with low reproductive success being associated with poor foraging conditions. A comparison of the breeding ecology of Arctic and Common Terns showed significant differences in reproductive strategy and output associated with differences in their sensitivities to changing conditions. Both clutch size and productivity were consistently lower in Arctic Terns than Common Terns. Chicks of both species hatched asynchronously with mortality increasing down the brood hierarchy. Younger sibling survival was impacted both by seasonal conditions and by elder sibling survival, although to varying degrees depending on species and hatching order. Arctic Terns foraged at a higher rate but on less energy rich prey and on a less varied diet. Both species increased provisioning and decreased parental attendance at the nest as chicks grew older, corresponding with the changes in chicks’ thermoregulatory abilities and energy requirements. Provisioning of chicks was primarily increased by selection of higher energy prey rather than through increased provisioning rate. Diurnal rhythms in either provisioning rate or diet were seen in both species, primarily associated with changing behaviour of prey fish. Temperature and precipitation affected provisioning, but adults maintained energy delivery to chicks. Increase in wind speed negatively impacted chick provisioning despite increased foraging effort. Chick mortality was linked to weather and feeding conditions, with high mortality linked to windy conditions and low provisioning. Yearly differences in productivity and chick mortality were associated with provisioning, and low parental attendance indicated poor foraging conditions. The reproductive output of both species is sensitive to declining foraging conditions and increased severity of weather conditions. The data implies that the sensitivity of Arctic Terns is greater than that of Common Terns, and that conditions around Coquet Island are sub-optimal for Arctic Tern breeding. ii Contents p2 Chapter 1. Recent changes in the marine environment and implications for seabird breeding success p2 1.1 Introduction p2 1.2 Climate change p3 1.3 Impact on the marine ecosystem p5 1.4 Monitoring change p6 1.4 Justification and aims of the study p12 Chapter 2. General methodology p12 2.1 Study site p13 2.2 Study nests p13 2.2.1 Enclosures p13 2.2.2 Clutch size, hatching success and productivity p14 2.2.3 Chick identification p14 2.3 Provisioning and parental attendance p14 2.3.1 Observations p15 2.3.2 Provisioning p17 2.3.3 Parental attendance p17 2.4 Data sources p17 2.4.1 Study data p17 2.4.2 RSPB clutch size and productivity data p17 2.4.3 Weather conditions p17 2.5 Licensing p19 Chapter 3. Differences in clutch size, hatching success and provisioning and their effects on productivity iii p19 3.1 Abstract p19 3.2 Introduction p22 3.3 Methodology and analysis p22 3.3.1 Methodology p22 3.3.2 Analysis p23 3.4 Results p23 3.4.1 Clutch size p25 3.4.2 Hatching success p26 3.4.3Productivity p30 3.4.4 Provisioning behaviour p32 3.5 Discussion p39 Chapter 4. The effects of brood size, hatching order and timing on chick mortality p39 4.1 Abstract p39 4.2 Introduction p43 4.3 Methodology and Analysis p43 4.3.1 Methodology p43 4.3.2 Analysis p44 4.4 Results p44 4.4.1 Seasonal trends: hatch day p45 4.4.2 Seasonal trends: mortality p48 4.4.3 Hatching order and chick mortality p51 4.4.4 Effect of brood size p52 4.4.5 Effect of younger siblings p53 4.4.6 Effect of older siblings p54 4.4.7 Hatching asynchrony p56 4.4.8 Inter-annual variation p60 4.5 Discussion iv p68 Chapter 5. The effects of age and number of chicks on provisioning and chick diet, and variations between species and year p68 5.1 Abstract p68 5.2 Introduction p70 5.3 Methodology and analysis p70 5.3.1 Methodology p70 5.3.2 Analysis p71 5.4 Results p71 5.4.1Species provisioning p71 5.4.2 Species diet p75 5.4.3 Chick age and provisioning behaviour p77 5.4.4 Chick age and diet p80 5.4.5 Brood size and provisioning behaviour p85 5.4.6 Year and provisioning behaviour p87 5.4.7 Year and diet p90 5.5 Discussion p97 Chapter 6. The effects of tidal and diurnal rhythms and weather on parental provisioning and chick diet p97 6.1 Abstract p97 6.2 Introduction p99 6.3 Methodology and analyses p99 6.3.1 Methodology p99 6.3.2 Analyses p100 6.4 Results p100 6.4.1 Tidal cycle and provisioning p102 6.4.2 Tidal cycle and diet p103 6.4.3 Diurnal rhythm and provisioning p108 6.4.4 Diurnal rhythm and diet p111 6.4.5 Effect of temperature p115 6.4.6 Effect of wind speed v p115 6.4.7 Effect of precipitation p117 6.5 Discussion p122 Chapter 7. The effects of chick’s age and weather on parental attendance at the nest site p122 7.1 Abstract p122 7.2 Introduction p124 7.3 Methodology and analyses p124 7.3.1 Methodology p124 7.3.2 Analyses p125 7.4 Results p125 7.4.1Age of chick p126 7.4.2 Inter-annual variation p129 7.4.3 Weather p135 7.5 Discussion p141 Chapter 8. The effects of weather and feeding conditions of chick mortality p141 8.1 Abstract p141 8.2 Introduction p143 8.3 Methodology and analyses p143 8.3.1 Methodology p143 8.3.2 Analyses p144 8.4 Results p144 8.4.1Mortlality between groups p145 8.4.2 Early-stage mortality p152 8.4.3 Mid-stage mortality p156 8.4.4 Late-stage mortality p158 8.5 Discussion vi p167 Chapter 9. Arctic and Common Tern breeding ecology: Cause for concern? p167 9.1 Breeding ecology p169 9.2 Provisioning Behaviour p171 9.3 Adult care of chicks p172 9.4 Impact of weather p173 9.5 Seasonal differences p176 9.6 Within season chick mortality p177 9.7 Causes of concern p179 9.8 Using breeding ecology to monitor change p182 References vii List of Tables p7 Table 1.1 General biometrics of adult Arctic and Common Terns p30 Table 3.1 Mann-Whitney U analysis of differences in provisioning behaviour of Arctic and Common Terns p32 Table 3.2 Mann-Whitney U analysis of differences in provisioning behaviour of Arctic and Common Terns averaged per nest p46 Table 4.1 Logistic regression of the effect of hatch day on survival outcome of 247 Arctic Tern chicks p46 Table 4.2 Logistic regression of the effect of hatch day on survival outcome of 330 Common Tern chicks p48 Table 4.3 Kaplan-Meier survival analyses of pre-fledging ages at death for Arctic and Common Terns depending on hatching order p48 Table 4.4 Kaplan-Meier survival analyses comparing pre-fledging ages at death of Arctic and Common Tern chicks overall and between a- and b-chicks p51 Table 4.5 Pearson’s Chi-squared analysis of the effects of brood size on mortality of Arctic and Common Tern chicks depending on hatching order p51 Table 4.6 Kaplan-Meier survival analyses of pre-fledging age at death of Arctic and Common Tern chicks depending on brood size p56 Table 4.7 Logistic regression of effect of length of hatching asynchrony on the mortality of Arctic and Common Tern chicks of different hatching order p57 Table 4.8 One-sided Fisher’s exact test testing for differences in number of chicks fledging or dying depending on hatching order, split between years viii p58 Table 4.9 Kaplan-Meier survival analyses of pre-fledging ages at death of Arctic and Common Tern chicks depending on year p58 Table 4.10 Kaplan-Meier survival analyses of pre-fledging age at death of a- and c-chick Common Terns p61 Table 4.11 Showing time from hatching by when 75% of deaths had occurred for Arctic and Common Tern chicks depending on hatching order p63 Table 4.12 Comparing percentage mortality of younger siblings after the death of an elder sibling with the mortality of an elder sibling p71 Table 5.1 Mean provisioning rate and rate of estimated energy delivery per nest and per chick and estimated energetic value per feed for Arctic and Common Terns p72 Table 5.2 Complete list of prey species brought to the nest by Arctic and Common Terns and percentage of diet they occupied p73 Table 5.3 Standardized test statistic from pair-wise analysis (adjusted p-value) from Kruskall-Wallis test of differences in proportions of different prey species brought to the nest by Arctic and Common Terns p75 Table 5.4 Kruskall-Wallis analysis of the effect of age of eldest chick on provisioning rate, energy delivery rate and energy per feed for both Arctic and Common Terns p77 Table 5.5 Spearman’s rho correlation of age of eldest chick in the nest with proportion of Sandeel, Clupeid, Small Fish, Shrimp (Arctic Terns only), Pipefish (Common Terns only) and ‘Other’ brought to the nest for Arctic and Common Terns p79 Table 5.6 Percentage of total fish of each size caught fed to chicks of each age group ix