SCOTTISH NATURAL HERITAGE TREND NOTE Number 021, October 2012 SEABIRDS IN SCOTLAND Prepared by Simon Foster and Sue Marrs of SNH Knowledge Information Management Unit using results from the Seabird Monitoring Programme and the Joint Nature Conservation Committee Scotland has internationally important populations of several seabirds. Their conservation is assisted through a network of designated sites. Figure 1 shows the distribution of the 50 Special Protection Areas (SPA) which have seabirds listed as a feature of interest. The map shows the widespread nature of the sites and the predominance of important seabird areas on the Northern Isles (Orkney and Shetland), where some of our largest seabird colonies are present. The most recent estimate of seabird populations was obtained from Birds of Scotland (Forrester et al., 2007). Table 1 shows the population levels for all seabirds regularly breeding in Scotland. Table 1: Population Estimates for Breeding Seabirds in Scotland. Figure 1: Special Protection Areas for Seabirds Breeding in Scotland. Species* Unit** Estimate Key Points Northern fulmar 486,000 AOS Manx shearwater 126,545 AOS Trends are described for 11 of the 24 European storm-petrel 31,570+ AOS species of seabirds breeding in Leach’s storm-petrel 48,057 AOS Scotland Northern gannet 182,511 AOS Great cormorant c. 3,600 AON Nine have shown sustained declines European shag 21,500-30,000 PAIRS over the past 20 years. Two have Arctic skua 2,100 AOT remained stable. Great skua 9,650 AOT The reasons for the declines are Black headed gull 43,200 AON complex – changes to food availability, Common gull 48,100 AON climate change and the effects of non- Lesser black-backed gull 25,000 AON native species Herring gull 72,100 AON Great black-backed gull 14,800 NESTS Black-legged kittiwake 282,200 AON Little tern 331 AON Sandwich tern 1,100 AON Common tern 4,800 AON Roseate tern 4 PAIRS Arctic tern 47,300 AON Common guillemot 791,400 PAIRS Razorbill 93,300 PAIRS Black guillemot 18,750 PAIRS Atlantic puffin 493,000 PAIRS * NOTE – Species in bold are those whose trends can be calculated and are detailed in this Trend Note ** NOTE – AOT = Apparently Occupied Territory; AOS = Apparently Occupied Common guillemots, Isle of May NNR Site; AON = Apparently Occupied Nest 1 © Lorne Gill SNH Seabird Trends Table 2: Changes in Abundance of Scotland’s Seabirds (1986 – 2011). Trends can be calculated for 11 of the 24 seabird species. Of these, nine of our Species % Change in Abundance commonest seabirds species have shown Northern fulmar ‐7 sustained declines over the past 20 years (Table 2). The reasons for the declines are complex European shag ‐47 and may be a result of changes in fishing effort Arctic skua ‐74 (resulting in changes to food availability), climate Herring gull ‐58 change (altering prey distributions and resulting Great black‐backed gull ‐53 in mortality of some species due to extreme weather events) and the effects of non-native Black‐legged kittiwake ‐66 species (such as rats on islands). Sandwich tern ‐48 Common tern ‐43 Arctic tern ‐72 Common guillemot ‐24 Black guillemot <+1* * Black guillemot trend is based on the change between the two national censuses (1982 – 1991 and 1999 – 2000) Atlantic puffin © Lorne Gill SNH Seabirds tend to be long lived and do not begin breeding until at least two or three years old (up to nine years in the case of northern fulmar), during which time some of these immature birds will remain at sea for long periods and occasionally visit the sites where they were reared (natal areas) and other sites (Votier et al., 2011). Our knowledge of seabird populations has been greatly improved by several long-term studies at colonies throughout Scotland. These include the Isle of May1, Canna, Rum, Eynhallow and Fair Isle. Three of these sites form part of the JNCC Key Monitoring Sites – Isle of May; Canna; and Fair Isle. Being long- lived species, studies of over 20 years are vital to improving our understanding of seabirds. Recent advances in technology are starting to yield further insights into the movements and behaviour of seabirds at sea (e.g. Frederiksen et al., 2012; Harris et al., 2009). In this Trend Note we explore the changes for individual seabird species and highlight the possible reasons for the changes that have been observed. Where data are available we present the indices for abundance and productivity. Abundance is the number of seabirds, productivity is the measure of breeding output – the number of chicks surviving to fledging. Productivity tends to change more quickly than abundance and can show within-season effects, whereas abundance shows changes in the numbers over longer time periods. Data Sources and Methods The data come from the Seabird Monitoring Programme. This is a partnership comprising volunteers and professionals who undertake monitoring at a number of Scotland’s seabird colonies each year. National censuses, which aim to count all seabirds around the UK coasts are undertaken periodically. The last census was in 1998 to 2002 (Mitchell et al., 2004). The counts and productivity data are collected using a defined set of methods (Walsh et al., 1995). The primary source of information for describing the pressures and threats that Scotland’s seabirds are facing is The Birds of Scotland (Forrester et al., 2007). All graphs and results presented were generated using data freely available online at the JNCC website (http://jncc.defra.gov.uk/docs/Data_points_1986-2011.xls). Maps were produced by the Geographic Information Group SNH. Job ID: 52938. © Reproduced by permission of Ordnance Survey on behalf of HMSO. © Crown copyright and database right 2012. All rights reserved. Ordnance Survey Licence number SNH 100017908. 1 www.ceh.ac.uk/sci_programmes/IsleofMayLong-TermStudy.html 2 Feeding and Nesting Preferences Seabirds have their own special requirements for feeding and breeding. A study by Parsons et al. (2006) matched the individual species to a range of groupings, such as whether they nested on cliffs, fed on sandeels or on discards. Table 3 summarises these feeding and nesting preferences for 11 seabird species. These are also summarised on each species account. Table 3: Seabird Species Groupings. Surface Sub- Sandeel Discard Inshore Offshore Cliff Flat- feeder surface specialist feeder feeder feeder nester ground feeder nester Northern fulmar X X X X * European shag X X X X * Arctic skua X X X X Black-legged kittiwake X X X X Sandwich tern X X X X Common tern X X X X Arctic tern X X X X Common guillemot X X X X * Black guillemot X X X X Herring gull X X X X X X Great black-backed gull X X X X X X *Note – although northern fulmar, European shag and common guillemot are listed as predominantly cliff nesters on some sites they do use flat ground for nesting Trend and Conservation Status Stable Amber LC Trend and Conservation Status SCOT BoCC IUCN For each seabird species there is a table summarising the trend and conservation status at Scotland, UK and International levels. SCOT – Trend for Scotland – Stable, Increasing or Declining. BoCC – Birds of Conservation Concern (Eaton et al., 2009) – UK assessment – Red list species show severe declines, Amber list species show moderate declines. IUCN – International Union for Conservation of Nature – A global assessment of the conservation status of species (www.iucn.org) – LC = Least Concern. Most of our seabirds come back to breed at the same sites year after year. This is often known as site faithfulness or site fidelity. One group of species, which are not quite as site faithful are the terns (Sandwich, Arctic and common). These can breed for many years at one site and then move to another area. Sometimes it may be possible to suggest why they have moved (e.g. American mink eating the chicks and eggs); at other times the reasons are not at all clear. Sandwich terns, Sands of Forvie NNR © The numbers of terns therefore can vary Lorne Gill SNH considerably from year to year at any individual colony. 3 Feeding and Nesting Preferences Trend and Conservation Status Stable Amber LC Surface Discard Offshore Cliff feeder feeder feeder nester SCOT BoCC IUCN Northern Fulmar The fulmar is a widespread breeding seabird. Fulmars are a relatively recent coloniser around the coast, having historically been restricted to St Kilda. In the late 1800s they began spreading and now they breed around Scotland’s coasts. They are amongst our longest-lived of seabirds; the oldest bird known is over 40 years old. There have been several long term studies undertaken on fulmars, perhaps most famous are the studies on Eynhallow (Dunnet, 1992), started in the 1950s and still running today. Technological advances have started to provide us with a greater understanding of fulmar movements throughout the breeding season. GPS tracking devices attached to fulmars by researchers from Aberdeen University has shown that some birds undertake long foraging (distance and duration) trips during the breeding season (http://www.abdn.ac.uk/lighthouse/blog/TransAtlantic- traveller/). Tasker (2007) listed the main threats to fulmars as being predation by brown rats and American mink, changes in food supply and long-line fishing. Fulmars are also susceptible to marine litter. The level of plastics contained in fulmars found dead is recorded and measured as part of a Europe-wide Ecological Quality Objective (EcoQO). http://qsr2010.ospar.org/media/assessments/EcoQO/EcoQO_09_Reduce_litter_in_fulmar_stomachs.pdf Since the start of the monitoring period the trend for fulmar has remained relatively stable. 600 500 400 300 200 100 Index of Abundance (1986=100%) Abundance of Index 0 1986 1992 1999 2005 2011 Figure 2: Northern fulmar breeding abundance (solid line) in Scotland (1986 to 2011) with 95% confidence limits (dotted line), and distribution across Scottish SPAs.