Resurvey reveals arrested population growth of the largest UK colony of European Storm-petrels Hydrobates pelagicus, Mousa, Shetland
* Correspondence author: email@example.com
1 RSPB Centre for Conservation Science, UK Headquarters, The Lodge, Sandy, Bedfordshire SG19 2DL, UK.
Playback resurvey of the UK’s largest breeding colony of European Storm-petrels Hydrobates pelagicus at Mousa, Shetland revealed that the substantial population growth achieved during previous decades has not been maintained. The estimated population size in 2015 was 10,778 apparently occupied sites (AOS) (95% confidence limits [CL] 8,857–13,207). The mean nesting density of birds breeding in natural habitat had declined substantially compared with 2008, but the area occupied by most sub-colonies had increased. Comparison with subcolonies surveyed in 2008 indicated a 12.8% decline, though the lack of precision that surrounds both surveys renders the decline statistically nonsignificant. We discuss the possible causes of the observed change in trend. The use of a new playback recording that did not include alarm calls was associated with a substantial increase in response rate compared with previous surveys. Daily response rates from nests of known occupancy status declined during the course of the fieldwork period, associated with increasing absence of adults at the nest during daylight, as chicks acquired thermoregulatory independence and adults remained at sea by day. We therefore use a date-specific calibration factor to estimate AOS density. Methods of data analysis were improved for the current survey to allow estimation of the number of AOS and associated CL for each subcolony separately. This resulted in a 51% reduction in the size of the confidence interval of the colony population estimate relative to the mean, compared with the 2008 survey. Playback surveys of burrow-nesting seabirds are typically characterised by low precision, which hinders statistically robust detection of population change, even when large declines are indicated. We recommend the adoption of a playback recording that does not include alarm calls, which may depress the frequency of responses or their detection by observers. Further, we suggest that for colonies where sub-colonies occur in discrete patches of habitat that are likely to vary in nesting density, the number of AOS should be estimated for each sub-colony separately. Adoption of these small modifications could substantially improve precision of playback surveys and hence the power to detect population change.
European Storm-petrels Hydrobates pelagicus breed on islands of the northeast Atlantic and Mediterranean with the largest populations occurring in the Faroes, Iceland, Ireland and the UK. The global population is estimated at around 1.5 million individuals (Brooke 2004). Although the current status of many colonies is not well known, the species is suspected to be in decline globally owing to predation by invasive species, pollution and development at breeding localities (Birdlife 2016). The first comprehensive, quantitative assessment of the breeding status of European Storm-petrels in Britain and Ireland was conducted during the Seabird 2000 census (Mitchell et al. 2004), which concluded that Britain and Ireland jointly held around 83,000 pairs in 95 surveyed colonies, with other unsurveyed colonies probably supporting several tens of thousands of additional pairs. Together the populations of Britain and Ireland represent 14–54% of the biogeographic population of the subspecies H. p. pelagicus. Since the Seabird 2000 census, rat eradication programmes have led to the establishment of several further colonies in the UK on islands that were formerly unsuitable (Ramsey, Lundy, St Agnes and Gugh). Notwithstanding these successes, resurvey of some of the largest UK colonies in recent years have indicated declines, (e.g. Priest island, Ross and Cromarty, West Scotland; Insley et al. 2014). The largest UK colony at the time of the Seabird 2000 census was Mousa, Shetland, holding 5,410 pairs in 1996 (estimate recalculated by Bolton et al. 2010), representing about 22% of the UK population at that time. Resurvey in 2008 indicated a substantial increase to 11,781 pairs (Bolton et al. 2010). Here we report results of a census conducted in 2015 and consider possible causes of the changes observed since 1996.
We thank Andy Simpkin, Joshua Murfitt, Louis Vandermaes and Newton Harper for help with fieldwork and the former Mousa boat ferry operators Jimmy Fullerton, Garry Sandison and Alan Pottinger for transport of personnel and equipment to the island. We thank Glen Tyler for assistance in provision of equipment and Kate Harding and Andy Stanbury for assistance in preparing figures. An earlier draft of this paper was improved by comments from Dr Allan Perkins, Dr Ana Sanz Aguilar, Helen Moncrieff, Steph Elliott and Natalie Pion.
The evolution of social behavior. Annual Review of Ecology and Systematics5: 325–383.
Population genetic structure and long-distance dispersal among seabird populations: Implications for colony persistence. Molecular Ecology 21: 2863–2876.
BirdLife International 2016. Species factsheet: Hydrobates pelagicus. http://www.birdlife.org Accessed 21 November 2016.
Regulation of seabird populations. British Ecological Society Symposium 25:147–167.
Playback re-survey and demographic modelling indicate a substantial increase in breeding European Stormpetrels Hydrobates pelagicus at the largest UK colony, Mousa, Shetland. Seabird 23: 14–24.
Population trends in Kittiwake Riss tridactyla colonies in relation to tick infestation Ibis 138: 326–334.
Birds and gas flares. Marine Pollution Bulletin. 10: 124–135.
Birds and North Sea oil and gas installations. Marine Pollution Bulletin 13: 5–6.
lbatrosses and Petrels across the World. Oxford University Press, Oxford, UK.
The breeding of the storm petrel. British Birds 50: 85–101 and 371–384.
Bootstrap Methods and Their Applications. Cambridge University Press, Cambridge.
http://www.snh.gov.uk/docs/A2181718.pdf). Scottish Natural Heritage. Accessed 3 October 2017.Noss NNR Annual Report 2016. (
http://ads.ahds.ac.uk/catalogue/ARCHway/volumeSelector.cfm?rcn=2917) Accessed 21 September 2017Notes of the brochs or Pictish towers of Mousa, Clickemin, &c., in Shetland, illustrative of part of the series of plans and sections deposited in the library of the Society. Archaeologia Scotica 5: 199–212. (
A retrap analysis of Storm Petrels tape-lured in Shetland. Ringing and Migration 4: 1–7.
Regional patterns of kittiwake Rissa tridactyla breeding success are related to variability in sandeel recruitment. Marine Ecology Progress Series 300: 201−211.
Regional and annual variation in black-legged kittiwake breeding productivity is related to sea surface temperature. Marine Ecology Progress Series 350: 137−143.
The demographic impact of extreme events: stochastic weather drives survival and population dynamics in a long-lived seabird. Journal of Animal Ecology 77: 1020–1029.
Seabird Ecology. Blackie, New York, NY, USA.
Seabird-fishery interactions: quantifying the sensitivity of seabirds to reductions in sandeel abundance, and identification of key areas for sensitive seabirds in the North Sea Marine Ecology Progress Series 202: 253–264.
Assessing vulnerability of marine bird populations to offshore wind farms. Journal of Environmental Management 119: 56–66.
Initial results of Storm Petrel Hydrobates pelagicus ringing in Portugal. Ringing and Migration 14: 133–134.
Mark-recapture and playback surveys reveal a steep decline of European Storm-petrels Hydrobates pelagicus at theblargest colony in western Scotland. R inging and Migration 29: 29–36.
Nestboxes: A successful management tool for the conservation of an endangered seabird. Biological Conservation 155: 39–43.
Disentangling the effects of predation and oceanographic fluctuations in the mortality of two allopatric seabird populations. Population Ecology 59: 225–238.
http://orca.cf.ac.uk/54124/1/U516649.pdf). Ph.D. Thesis, CardiffThe Migration Strategy, Diet & Foraging Ecology of a Small Seabird in a Changing Environment (
Ectoparasite Eefects of nestling European Storm-petrels. Waterbirds 22: 297–301.
Predator avoidance behaviour in a nocturnal petrel exposed to a novel predator Ibis 155:16–31.
Seabird Populations of Britain and Ireland. Results of the seabird 2000 census (1998−2002). T & A.D. Poyser, London.
Seabirds and sandeels: the conflict between exploitation and conservation in the northern North Sea. Biodiversity and Conservation 1: 98–111.
Effects of changes in food availability on reproductive effort in Arctic terns. Ardea 80: 71–81.
Ages of Storm-petrels Hydrobates pelagicus prospecting potential breeding colonies. Ringing and Migration 22: 205–208.
Testing the use of infra-red video cameras to census a nocturnal burrow-nesting seabird, the European Storm Petrel Hydrobates pelagicus. Ibis DOI: 10.1111/ibi.12539.
Using dual-sex calls improves the playback census method for a nocturnal burrow-nesting seabird, the Manx Shearwater Puffinus puffinus. Bird Study 64: 146–158.
The status of Storm-petrels Hydrobates pelagicus on Mousa, Shetland. Unpublished RSPB Report, Sandy, UK.
Development of playback census methods for Storm-petrels Hydrobates pelagicus. Bird Study 45: 302–312.
Bird interactions with offshore oil and gas platforms: Review of impacts and monitoring techniques. Journal of Environmental Management 147: 34–45.
Flare up over North Sea birds. New Scientist 81: 464–466.
Evidence-based culling of a facultative predator: efficacy and efficiency components. Biological Conservation. 142: 424–431.
http://www.snh.org.uk/pdfs/publications/nnr/Noss_NNR_The_Reserve_Story.pdf). Scottish Natural Heritage, Lerwick. Accessed 21 September 2017.The Story of Noss National Nature Reserve (
http://www.sccs.org.uk/images/expertise/reports/co2-eor-jip/SCCS-CO2-EOR-JIP-WP11-Flaring-Venting.pdf) Scottish Carbon Capture and Storage, Edinburgh. Accessed 22 September 2017.A review of Flaring and Venting at UK Offshore Oilfields (
The wreck of leach’s storm petrels on the Portuguese coast in the autumn of 1983. Ringing and Migration 8: 27–28.
Seabird foraging ranges as a preliminary tool for identifying candidate Marine Protected Areas. Biological Conservation 156: 53–61.
Out of sight but not out of harm’s way: Human disturbance reduces reproductive success of a cavity-nesting seabird. Biological Conservation 174: 127–133.
Seabirds at risk around Offshore Oil Platforms in the North-west Atlantic. Marine Pollution Bulletin 42: 1285–1290.
A method of assessing seabird vulnerability to surface pollutants. Ibis 137: S147–S152.
Repeat playback census of breeding European Storm-petrels Hydrobates pelagicus on the Skokholm and Skomer SPA in 2016. NRW Evidence Report 190, Natural Resources Wales, Cardiff.