Background: Natural environments are dynamic systems with conditions varying across years. Higher trophic level consumers may respond to changes in the distribution and quality of available prey by moving to locate new resources or by switching diets. In order to persist, sympatric species with similar ecological niches may show contrasting foraging responses to changes in environmental conditions. However, in marine environments this assertion remains largely untested for highly mobile predators outside the breeding season because of the challenges of quantifying foraging location and trophic position under contrasting conditions.
Method: Differences in overwinter survival rates of two populations of North Sea seabirds (Atlantic puffins (Fratercula arctica) and razorbills (Alca torda)) indicated that environmental conditions differed between 2007/08 (low survival and thus poor conditions) and 2014/15 (higher survival, favourable conditions). We used a combination of bird-borne data loggers and stable isotope analyses to test 1) whether these sympatric species showed consistent responses with respect to foraging location and trophic position to these contrasting winter conditions during periods when body and cheek feathers were being grown (moult) and 2) whether any observed changes in moult locations and diet could be related to the abundance and distribution of potential prey species of differing energetic quality.
Results: Puffins and razorbills showed divergent foraging responses to contrasting winter conditions. Puffins foraging in the North Sea used broadly similar foraging locations during moult in both winters. However, puffin diet significantly differed, with a lower average trophic position in the winter characterised by lower survival rates. By contrast, razorbills' trophic position increased in the poor survival winter and the population foraged in more distant southerly waters of the North Sea.
Conclusions: Populations of North Sea puffins and razorbills showed contrasting foraging responses when environmental conditions, as indicated by overwinter survival differed. Conservation of mobile predators, many of which are in sharp decline, may benefit from dynamic spatial based management approaches focusing on behavioural changes in response to changing environmental conditions, particularly during life history stages associated with increased mortality.
We thank Scottish Natural Heritage for permission to work on the Isle of May National Nature Reserve, Carrie Gunn and Mark Newell for help with data collection, Stephen Freeman and Kate Searle for help with analysis of survival data. We thank R McGill and J Newton for help with stable isotope analysis at the NERC Life Sciences Mass Spectrometry Facility node East Kilbride (UK). We are grateful to B Harley (Cefas) for collection of pipefish for isotopic analyses. We thank U Struck and M Falk for SIA at the Leibniz Institute for Research on Evolution and Biodiversity (Berlin, FRG). We also thank Kirsteen MacKenzie and Cefas for the sample collection and initial North Sea isoscape construction. Peter Thompson and Paula Redman provided valuable technical assistance in isotope analysis.
K.S.G is jointly funded through the SPITFIRE Natural Environment Research Council (NERC) DTP partnership (grant number 1498919) and Southampton Marine and Maritime Institute (SMMI). This work was also supported by NERC funding for UK National Capability including award number NE/R016429/1 as part of the UK-SCaPE programme, the NERC/Department for Environment, Food and Rural Affairs (DEFRA) Marine Ecosystems Research Programme (award number NE/L003082/1), SEATRACK (http://www.seapop.no/en/seatrack/) and the Joint Nature Conservation Committee (JNCC).. BK was supported by the EURopean network of excellence for OCean Ecosystems ANalysiS (EUROCEANS), the Department for Environment, Food and Rural Affairs (DEFRA, UK, contract ME3205), and through baseline funds of BH Jones (KAUST) during the writing phase of this manuscript. We thank the Scottish Universities Environmental Research Centre (SUERC) for funding of stable isotope analysis at the NERC Life Sciences Mass Spectrometry Facility node East Kilbride (UK).
KSG, CNT, SW and MPH conceived the project. SW, MPH, FD, KEE, HS, JRS and BK planned and undertook the fieldwork. KSG carried out the sample and data analysis and wrote the manuscript. All authors provided editorial advice. All authors read and approved the final manuscript.
- Fratercula arctica
- Alca torda
- Marine spatial management
- Spatial ecology
- Seabird foraging behaviour
- North Sea
- Trophic ecology