DOI: 10.5061/dryad.v056r5h
title: Data from: Combined bottom-up and top-down pressures drive catastrophic population declines of Arctic skuas in Scotland

description: 1. Understanding drivers of population change is critical for effective
 species conservation. In the northeast Atlantic Ocean, recent changes
 amongst seabird communities are linked to human and climate change impacts
 on foodwebs. Many species have declined severely, with food shortages and
 increased predation reducing productivity. Arctic skua Stercorarius
 parasiticus, a kleptoparasite of other seabirds, is one such species. 2.
 The aim of the study was to determine relative effects of bottom-up and
 top-down pressures on Arctic skuas across multiple colonies in a rapidly
 declining national population. 3. Long-term monitoring data were used to
 quantify changes in population size and productivity of Arctic skuas,
 their hosts (black-legged kittiwake Rissa tridactyla, common guillemot
 Uria aalge, Atlantic puffin Fratercula arctica, Arctic tern Sterna
 paradisaea), and an apex predator (great skua Stercorarius skua) over 24
 years (1992–2015) in Scotland. We used digital mapping and statistical
 models to determine relative effects of bottom-up (host productivity) and
 top-down (great skua density) pressures on Arctic skuas across 33
 colonies, and assess variation between three colony types classified by
 host abundance. 4. Arctic skuas declined by 81% and their hosts by 42–92%,
 whereas at most colonies great skuas increased. Annual productivity
 declined in Arctic skuas and their hosts, and reduced Arctic skua breeding
 success was a driver of the species’ population decline. Arctic skua
 productivity was positively associated with annual breeding success of
 hosts, and negatively with great skua density. Inter-colony variation
 suggested Arctic skua trends and productivity were most sensitive to
 top-down pressures at smaller colonies of host species where great skuas
 had increased most, whereas bottom-up pressures dominated at large
 colonies of host species. 5. Scotland’s Arctic skua population is
 declining rapidly, with bottom-up and top-down pressures simultaneously
 reducing breeding success to unsustainably low levels. Marine food web
 alterations, strongly influenced by fisheries management and climate
 change, are driving the decline, and this study demonstrates severe
 vulnerability of seabirds to rapid change in human-modified ecosystems.
 Potential but untested conservation solutions for Arctic skuas include
 Marine Protected Areas, supplementary feeding within colonies, and
 management of great skuas.
description: Raw data on species
 population size and breeding success per colony per yearPerkins_ArcticSkua_0001_RawData_22July2018.xlsCleaned data for analysing population trendsPerkins_ArcticSkua_001_DataPopulationTrends_22July2018.xlsCleaned data for analysing productivity trendsPerkins_ArcticSkua_002_DataProductivityTrends_22July2018.xlsDataset for analysing associations with Arctic skua population trendsPerkins_ArcticSkua_003_DataPopulationTrendAssociations_22July2018.xlsDataset for analysing associations with Arctic skua productivityPerkins_ArcticSkua_004_DataProductivityAssociations_22July2018.xlsSAS code for analysing population trendsPerkins_ArcticSkua_005_CodePopulationTrends_22July2018.txtSAS code for analysing productivity trendsPerkins_ArcticSkua_006_CodeProductivityTrends_22July2018.txtSAS code for analysing associations with Arctic skua population trendsPerkins_ArcticSkua_007_CodePopulationTrendAssociations_22July2018.txtSAS code for analysing associations with Arctic skua productivityPerkins_ArcticSkua_008_CodeProductivityAssociations_22July2018.txtModel outputs and graphs for population trendsPerkins_ArcticSkua_009_ResultsPopulationTrends_22July2018.xlsModel outputs and graphs for productivity trendsPerkins_ArcticSkua_010_ResultsProductivityTrends_22July2018.xlsModel outputs and graphs for associations with Arctic skua population trendsPerkins_ArcticSkua_011_ResultsPopulationTrendAssociations_22July2018.xlsModel outputs and graphs for associations with Arctic skua productivityPerkins_ArcticSkua_012_ResultsProductivityAssociations_22July2018.xls