Using stable isotopes to assess climate-change impacts on migrations of prions (Aves:Procellariiformes)

Lead Research Organisation: NERC British Antarctic Survey
Department Name: Science Programmes

Abstract

Global warming has resulted in much faster and more pronounced ecological responses in marine than in terrestrial ecosystems. Yet most people are unaware of the dramatic changes going on in marine ecosystems because these are not readily observed from land. For example, oceanic copepod distributions have been found to be moving poleward 30 times faster than terrestrial animal distributions. Copepods are extremely abundant animals and are a key food resource in high latitude oceans. As ocean temperatures increase, high densities of large and nutritious copepods in cold waters are replaced by smaller and less nutritious species of warm-water copepods. Seabirds that specialize on a diet of large copepods may experience dramatic changes in the distribution of their main winter prey within the timescale of a single generation of these long-lived birds. This is potentially one of the most severe and rapid impacts of climate change on any vertebrates. Prions or "whale-birds" are southern oceans petrels that breed on subAntarctic islands. Prions are extremely abundant seabirds, and many of the largest colonies are on UK dependent territories such as South Georgia (for example over 20 million pairs on South Georgia) and Tristan da Cunha where colonies are protected by international conservation conventions. Due to their numerical abundance these small burrowing species are major consumers and therefore a change in their distribution or abundance has considerably knock-on effects for marine ecosystems. They have a highly specialized bill morphology evolved for filter feeding. Prion species differ in bill morphology, with the extent of dependence on copepods most pronounced in the broad-billed prion, and least in Antarctic prion and closely related blue petrel. We can infer the latitude where these birds spend the winter because in the southern hemisphere there is a very strong latitudinal gradient in carbon isotope ratios in marine foods. This enables tracking of wintering areas used by these birds. Feathers grown during the autumn/winter moult will have carbon isotope signatures that reflect the latitude where the birds were feeding while their feathers grew. Feathers collected from birds at their breeding sites can therefore be used to infer the main moulting/wintering regions visited by each individual bird. Analysis of historical samples (from museum collections) permits wintering latitudes used by these species in the past to be inferred in a similar way. We will validate the use of isotopes to infer wintering latitude by deploying small data loggers on a sample of prions to determine wintering areas using light level data recorded by the logger, a well established method already used on many seabirds, so we can measure isotopes in individuals with known wintering area. The key hypothesis we will test is that broad-billed prions have changed winter distribution in recent years to spend the austral winter at higher latitudes south of their breeding colonies, whereas in the past (from 150 years ago up until some time in the late 20th century) these birds migrated north from their breeding grounds to winter at lower latitudes in the southern hemisphere. We will also test the hypothesis that other prions show less poleward movement of winter areas (which we expect because they are less dependent on a copepod diet). Finally, we will test the hypothesis that poleward movement of broad-billed prions varies from year to year in relation to copepod distribution and density in each different year (data that are available for recent years from a Southern Ocean plankton database). This research will highlight a major impact of global warming on an important marine food web and will also inform conservation policy during this time of rapid ocean warming and changing copepod distribution.

Planned Impact

See lead proposal
 
Description Migratory marine predators are vulnerable to climate-induced changes in prey phenology and abundance as they move between breeding and non-breeding areas to target resources that are seasonal but spatio-temporally predictable. In the Southern Ocean, small petrels are major consumers of zooplankton, but perturbations in the ecosystem through ocean warming are altering food-web structure and have been linked to poleward shifts in the distribution of cold-water zooplankton species. This project has resulted in three key outputs.
In the first study, we focussed on two small congeneric petrels; the broad-billed prion Pachyptila vittata, and the Antarctic prion P. desolata. We investigated historical trends in non-breeding distribution by analysing feather stable isotope ratios from a time-series dating back to 1926, and examined contemporary broad-billed prion non-breeding distributions using miniaturised geolocation-immersion loggers. After controlling temporally for the Suess effect, we found that the d13C signatures of Antarctic prions, but not broad-billed prions, declined during the study period. This suggests that Antarctic prions may have shifted their non-breeding distribution southward over the last century. Both species exhibited significant declines in d15N during the same period, indicative of long-term decreases in productivity, or changes in the trophic structure of prey communities. Tracked broad-billed prions migrated c. 1000 km to an area east of the breeding colony where the Louisville seamount chain bisects the subtropical front. Topographically-driven upwellings are stable and predictable features and may be crucial in aggregating plankton. Targeting seamounts could therefore mitigate the impact of climate-induced prey shifts by providing refugia for the more planktivorous broad-billed prion.
Prions Pachyptila species are closely-related genetically, and the distinguishing phenotypic characteristics relate to the divergent bill morphology, which results in differing degrees of dietary specialisation. We wanted to examine whether the latter might drive differences in current migratory patterns within the genus. Recent evidence suggests that the species may segregate spatially during the non-breeding season, but currently little is known of the habitat preferences that may explain these patterns. In the second component of the project, we compared the migratory strategies and non-breeding habitat preferences of four species of petrel; the Antarctic prion, broad-billed prion, fulmar prion P. crassirostris, and a similarly-sized ecological analogue, the blue petrel Halobaena caerulea from colonies across the Southern Ocean. Our findings showed clear spatial separation during the non-breeding period that reflected differences in the ocean temperature experienced by the birds. This may have important implications into the future as the oceans warm, but further work is required to better understand these processes.
Finally, as studies of avian migration increasingly use stable isotope analysis to provide vital trophic and spatial markers, we examined sources of variation in these type of results. A fundamental question remains about the consistency in stable isotope ratios within and between feathers from the same individual. We examined variation in carbon and nitrogen isotopes by sub-sampling feathers collected from the wings of adults of two small congeneric petrel species; broad-billed and Antarctic prions. Broad-billed prion feather vane material was enriched in 15N compared to feather rachis material, but there was no detectable difference in ?13C. Comparison of multiple samples taken from Antarctic prion feathers indicated subtle difference in isotope ratios; rachis material was enriched in 13C compared to vane material, and there were differences along the length of the feather, with samples from the middle and tip of the feather depleted in 15N compared to those from the base. While the greatest proportion of model variance was explained by differences between feathers and individuals, the magnitude of these within-feather differences was up to 0.5 ‰ in ?15N and 0.8 ‰ in ?13C. We discussed the potential drivers of these differences, linking isotopic variation to individual-level dietary differences, movement patterns and temporal dietary shifts. A novel result was that within-feather differences in ?13C may be attributed to differences in keratin structure within feathers, suggesting further work is required to understand the role of different amino-acids. Our results highlight the importance of multiple sampling regimes that consider both within and between-feather variation in studies using stable isotopes.
Exploitation Route As a spur to future research, and in terms of understanding impacts of global climate change on marine ecosystems
Sectors Environment

 
Description World Seabird Conference Travel Awards
Amount $840 (USD)
Organisation World Seabird Union 
Sector Learned Society
Country Global
Start 10/2015 
End 10/2015
 
Description Collaboration with Peter Ryan 
Organisation University of Cape Town
Department Percy FitzPatrick Institute of African Ornithology
Country South Africa 
Sector Academic/University 
PI Contribution Analyses comparing habitat preferences of grey-headed albatrosses from colonies in the South Atlantic and Indian oceans
Collaborator Contribution Peter Ryan from the University of Cape Town, South Africa, provided tracking data and expert advice that has assisted towards the publication of a paper (Clay et al. 2016).
Impact Scientific paper (Clay et al. 2016). Web article on the results "Albatrosses forage in different areas when on migration", URL - https://phys.org/news/2016-07-albatrosses-forage-areas-migration.html
Start Year 2013
 
Description Collaboration_prion grant 
Organisation Museum of New Zealand Te Papa Tongarewa
Country New Zealand 
Sector Charity/Non Profit 
PI Contribution Involvement in research
Collaborator Contribution Provision of samples, data and expertise
Impact Papers published and in prep
Start Year 2012
 
Description Collaboration_prion grant 
Organisation National Institute of Water and Atmospheric Research (NIWA, New Zealand)
Country New Zealand 
Sector Public 
PI Contribution Involvement in research
Collaborator Contribution Provision of samples, data and expertise
Impact Papers published and in prep
Start Year 2012
 
Description Collaboration_prion grant 
Organisation New Zealand Department of Conservation
Country New Zealand 
Sector Private 
PI Contribution Involvement in research
Collaborator Contribution Provision of samples, data and expertise
Impact Papers published and in prep
Start Year 2012
 
Description Collaboration_prion grant 
Organisation Victoria University of Wellington
Country New Zealand 
Sector Academic/University 
PI Contribution Involvement in research
Collaborator Contribution Provision of samples, data and expertise
Impact Papers published and in prep
Start Year 2012
 
Description Glasgow Science Festival 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact Public engagement activity for Glasgow Science Festival that explained the project and discussed seabird migration, diet and climate change
Year(s) Of Engagement Activity 2014
 
Description Interview for NERC Planet Earth Podcast 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Media (as a channel to the public)
Results and Impact Podcast
Year(s) Of Engagement Activity 2012
URL http://planetearth.nerc.ac.uk/multimedia/story.aspx?id=1261
 
Description Podcast (Naturally Speaking) 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Media (as a channel to the public)
Results and Impact Blog podcast
Year(s) Of Engagement Activity 2015
URL https://naturallyspeakingpodcast.wordpress.com/2015/03/02/you-are-what-you-eat
 
Description School Visit (Hills Road Sixth Form) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact Talk to raise awareness on the impact of Human activities on biodiversity extinction and more specifically the role we have as citizens to influence fisheries and climate change
Year(s) Of Engagement Activity 2016