Soteag Ornithological Monitoring Programme
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SOTEAG ORNITHOLOGICAL MONITORING PROGRAMME 2013 SUMMARY REPORT Martin Heubeck and Mick Mellor, Aberdeen Institute of Coastal Science and Management, University of Aberdeen. January 2014 CONTENTS Page 2013 Executive Summary 2 1. Monitoring of cliff-breeding seabirds 1.1. Weather 4 1.2. Northern Fulmar Fulmarus glacialis: Population counts 5 1.2. Northern Fulmar Fulmarus glacialis: Breeding success 6 1.3. European Shag Phalacrocorax aristotelis: Population counts 8 1.3. European Shag Phalacrocorax aristotelis: Breeding success 10 1.4. Black-legged Kittiwake Rissa tridactyla: Population counts 12 1.4. Black-legged Kittiwake Rissa tridactyla: Breeding success 13 1.5. Common Guillemot Uria aalge: Population counts 16 1.5. Common Guillemot Uria aalge: Breeding success at Sumburgh Head 18 1.5. Common Guillemot Uria aalge: Breeding success at Burravoe, Yell 21 1.6. Razorbill Alca torda: Population counts 22 1.6. Razorbill Alca torda: Breeding success at Sumburgh Head 23 2. Pre-breeding counts of Black Guillemots Cepphus grylle 24 3. Breeding Red-throated Divers Gavia stellata in Northmavine 27 4. Moulting Common Eiders Somateria mollissima in Yell Sound and Sullom Voe 28 5. Winter counts of diving seabirds and seaduck 5.1. Sullom Voe and Southern Yell Sound 29 5.2. Hascosay, Bluemull and Colgrave Sounds, and South Unst 30 5.3. Pool of Virkie to Bay of Quendale 31 5.4. Burra, Trondra and the Scalloway Islands 32 6. Beached Bird Surveys 6.1. Incidence of oiling 33 6.2. Non-oiled mortality 36 7. 2013 Publications and Presentations 38 8. Acknowledgements 38 Appendix 1. Seabird monitoring on Foula in 2013 39 1 2013 Executive Summary 1. Monitoring of cliff-breeding seabirds Northern Fulmar Fulmarus glacialis. There was little change since 2012 in the number of apparently occupied sites (AOS) at the four colonies monitored. Breeding success at these colonies was relatively high: 0.48 ± 0.02 SE by the mean June count method, 0.55 ± 0.03 by the marked photograph method. European Shag Phalacrocorax aristotelis. Non-breeding in southeast Mainland was even more extensive than in 2011-12. Counts from Sumburgh Head north to Mousa found 71% fewer nests (251, 42% active) than in 2010 (877, 97% active), and 52% fewer adults (593 vs. 1,244). The breeding season appeared more normal in southeast Yell where counts of adults (185) and nests (137, 91% active) were 17% and 22% lower than in 2009 (222 adults, 176 nests, 99% active). Along two stretches of coast on Fetlar, counts of adults (141) and nests (105, 72% active) were also only 23% and 17% lower than on the previous survey in 2002 (184 adults, 126 nests, 94% active). At Sumburgh Head, laying was late and very asynchronous, the proportion of nests that progressed to incubation (57%), and the proportion of these at which young were seen (16%) were the lowest yet recorded, as was breeding success (0.27 young fledged per laying pair). Laying was 5-6 weeks earlier at Burravoe, Yell, where 93% of nests progressed to incubation, chicks were seen at 64% of these, and success was a moderate 0.92. Black-legged Kittiwake Rissa tridactyla. On Fetlar, there were 64 nests (91% active) at one breeding station, compared to 41 nests at three stations on the last visit, in 2002. The total of 149 nests (82% active) at southeast Yell was similar to the last visit (154), in 2009. In southeast Mainland, the total of 204 nests (65% active) at Mousa (deserted), No Ness, Troswick Ness and Boddam was almost half that in 2010 (392), while the total at Compass and Sumburgh Heads, and nearby Horse Island (499, 56% active) was 26% lower than in 2010 (673). The overall total of 1,059 nests counted in 2013 was 91% lower than at the same breeding stations in the baseline year of 1981 (11,947). Breeding success was monitored at six colonies. Laying was late, and most breeding attempts failed at the late incubation and early chick stages, in late June and early July. Success was zero at Sumburgh Head, No Ness and Hich Holm, 0.08 at Compass Head, 0.29 at Ramna Geo, and 0.12 at Burravoe, Yell; 2013 was the fourth successive year of extensive breeding failure. Common Guillemot Uria aalge. Numbers were lower than in 2012 at the four colonies monitored, with 2013 population indices (1978 = 100) of 46.0 at Sumburgh Head, 39.5 at Troswick Ness, 1.5 at Esha Ness, and 41.8 at Burravoe, Yell. Colony attendance at Sumburgh Head was the most variable yet recorded, with a 50% difference in numbers in plots on 1st and 4th June, while a whole colony count there on 10th June recorded 6,279 birds, 14% fewer than on 11th June 2012 (7,307). Breeding success was monitored in single plots at Sumburgh Head and Burravoe, Yell. At Sumburgh, the proportion of regularly attended sites at which eggs were laid (63%) was the lowest yet recorded. Incubating birds seemed food-stressed, some abandoning eggs after apparent continuous shifts of 3-4 days. Only 11% of first eggs, and no relay eggs hatched and no chicks survived to fledge. Some chicks fledged from other parts of the colony but overall success was probably no higher than 0.05. At Burravoe, eggs were assumed to have been laid at only 58% of regularly attended sites, but chicks were seen at 40% of these, most survived to fledge, and success was estimated at 0.36 per laying pair, low by national standards but considerably higher than at Sumburgh. Razorbill Alca torda. Plot counts at Sumburgh Head (2013 mean of 77 birds) suggest little change in numbers since 2007, after a 70% decrease during 2000-07, and a total colony count on 10th June was of 151 birds (189 on 11th June 2012). Few were present at the other colonies monitored, with mean counts of 2 at Troswick Ness, 5 at Esha Ness and 8 at Burravoe. Breeding success of 43 assumed or known egg-laying pairs at Sumburgh Head was 0.23, lower than in 2012 (0.56) but higher than in 2011 (zero). 2. Pre-breeding counts of Black Guillemots Cepphus grylle Counts were made at 12 of the 13 monitored stretches of coast. Along five sections, numbers were slightly (6-10%) lower than in 2012, markedly (23%) lower than in 2011 at one (Ronas Voe), and very similar (-1% to +3%) to 2011/12 at four; sea conditions meant counts on two sections were useless for monitoring purposes. Allowing for counts made in difficult conditions, numbers in 2011-13 were about 15-20% higher than in 2005-07. 2 3. Breeding Red-throated Divers Gavia stellata in Northmavine The number of breeding pairs (26), lochs with nests (30), and lochs with divers present (41) in the study area were the highest since the early 1980s. Eight pairs fledged 10 young, rather low success of 0.38. 4. Moulting Common Eiders Somateria mollissima in Yell Sound and Sullom Voe Counts from land located 494 birds in southern Yell Sound (7th August), all in Dales Voe and Colla Firth, and 118 in Sullom Voe (21st August), all in the northern half of the voe. Based on the 2012 census results, the total of 612 birds represented 13% of the Shetland population. 5. Winter counts of diving seabirds and seaduck Surveys of standard areas were made on four dates in January and early February (three by boat, one from land) and complemented counts made of other areas in December 2012. Counts exceeding Great Britain thresholds for sites of national importance were of 555 Long-tailed Ducks (threshold 110) in Colgrave Sound, 124 Red-breasted Mergansers (threshold 84) and 21 Slavonian Grebes (threshold 11) in Sullom Voe, 43 Great Northern Divers (threshold 25) between Pool of Virkie and Bay of Quendale, and 31 Great Northern Divers and 20 Slavonian Grebes around Burra, Trondra and the Scalloway Islands. 6. Beached Bird Surveys Of the total of 745 seabirds found dead during the year, 49 (6.6%) were oiled: 29 Fulmars, 4 Gannets, 3 Common Gulls, 5 Kittiwakes, 7 Common Guillemots. Eleven samples of oil were analysed: 2 were unrefined crude oils (1 Murchison/Statfjord, 1 Ninian), 9 were refined fuel oil residues. Few pelagic auks were found during winter 2012/13. In summary, there was no evidence that the operation of the Sullom Voe Terminal, or its associated tanker traffic, had any detrimental impact on Shetland’s seabird populations during 2013. 3 1. Monitoring of cliff-breeding seabirds 1.1. Weather Weather can influence the ability to carry out seabird monitoring, and in extreme cases, can directly affect seabirds’ breeding success. High pressure over Shetland in late March continued into early April, and the settled conditions allowed a good start to the pre-breeding counts of Black Guillemots. This broke down on 13th, after which a series of Atlantic lows brought wet and windy weather, allowing only one more morning of counting Black Guillemots, on 26th April. May began with a southwesterly severe gale, and while continued cool and unsettled weather throughout the month did not seem to cause any problems for breeding birds or hamper fieldwork greatly, it often made the latter unpleasant. The first 11 days of June were fairly dry and settled, allowing a good start to the population plot counts, while light south-westerly winds on 18- 19th enabled Zodiac surveys of Yell and Fetlar, the first survey of the latter for 11 years. Strong easterly winds and heavy rain on 22nd resulted in further losses of the few remaining eggs and chicks in the Common Guillemot breeding success plot at Sumburgh Head.