IAP-25-114

Understanding how a threatened seabird moves across complex ocean energyscapes

The movements made by animals are a critical determinant of their access to resources and exposure to threats, with movement being one of the key primary responses of individuals to environmental change. Thus, understanding how individuals adjust their movement behaviour in response to changing environmental conditions is an essential step in linking environmental change to energetic and demographic consequences for individuals and ultimately populations (Nathan et al. 2008).

Seabirds are the most threatened group of birds globally (Dias et al. 2019), being exposed to a wide array of anthropogenic pressures. They are also often highly mobile, exhibiting very large-scale movements, particularly in the non-breeding season. Though there are documented areas characterised by winter seabird aggregations (Davies et al. 2021), we often do not know why these areas are suitable for non-breeding birds. It is apparent that individuals can differ markedly in their destination and/or in the specific route taken to reach a common destination (Fayet et al. 2016, Phillips et al. 2017) and movements can vary in response to changing environmental conditions (Siddiqi-Davies et al. 2024). The non-breeding period is a critical one for seabird species in temperate regions, with the winter representing an energetically demanding period of the annual cycle due to lower temperatures, poor weather, reduced food availability, and shorter daylengths (Daunt et al. 2006, Fort et al. 2009). These factors can lead to conditions that directly impact on survival (Grosbois & Thompson 2005, Reiertsen et al. 2014) or can indirectly impact on subsequent breeding success via carry-over effects (Fayet et al. 2017). Although there have been some recent studies investigating seabird energy expenditure during the non-breeding season (Dunn et al. 2020, Buckingham et al. 2023, Leandri-Breton et al. 2025), understanding of how individual movement patterns affect both energy expenditure and energy gain, and what this may mean for survival or reproduction, is very limited. Consequently, we have limited knowledge of how changing marine conditions may affect individual energy balances and consequently lead to demographic impacts. This is primarily due to (i) historical challenges associated with gathering large and long-term biologging datasets for seabirds in the non-breeding season, from which movements and energetics can be estimated, and (ii) difficulties in linking seabird movement data with measures of energy gain (i.e., prey abundance and distribution).

This project will begin to fill this knowledge gap by bringing together a rarely available extensive paired biologging (geolocation-immersion loggers) and demographic dataset collected across 18 years for black-legged kittiwakes (Rissa tridactyla) from the Isle of May, Scotland, with a unique spatio-temporal food abundance dataset. This dataset captures the large zooplankton energy across the kittiwake’s non-wintering range, with prior diet and stable isotope analyses indicating that zooplankton are often a significant component of the diet in non-breeding kittiwakes (Braune 1987, Lydersen et al. 1985, Charrier et al. 2024). In bringing these data together, this project will reveal how individuals both expend and gain energy as they move throughout the non-breeding season and how they respond to environmental conditions. It will also provide a rare examination of the potential consequences of non-breeding season movements for later breeding success. Specifically, the project will explore four key questions:

1. How do individuals gain and expend energy across their non-breeding season movements and how are these patterns predicted by oceanographic conditions?
2. To what extent do individuals vary in the timing, route, or destination of non-breeding season movements, and how does this relate to patterns of energy expenditure and gain?
3. Do differences in energy expenditure or gain have consequences for subsequent timing of breeding and productivity?
4. How are the drivers of kittiwake movements and energetics predicted to change in the future?

The project will utilise a long-term dataset on year-round at-sea locations, activity and demography of black-legged kittiwakes, collected by UKCEH in partnership with the international SEATRACK programme (https://seatrack.net/). The dataset from a breeding colony in SE Scotland (Isle of May) spans 2007-2025 and will allow the student to conduct novel research on the drivers of seabird movement behaviour, energetics and habitat use during the non-breeding season and link these to subsequent demographic rates.

The tracking of seabirds during the non-breeding season relies on the use of global location sensors (GLS) due to their small size and method of attachment which enables year-round tracking (something that is largely impossible to achieve for many seabird species using GPS). These loggers measure ambient light levels but can be paired with other sensors including saltwater immersion. The information on light intensity can be used to estimate a tag’s geographic location based on equations on the position of the sun in relation to the Earth’s rotation. The collected saltwater immersion data can be used to estimate daily activity and energy budgets by allowing the calculation of the daily duration of different behaviours (flight, active foraging, resting on water) and combining of this information with published data on activity-specific metabolic rates. Body mass and productivity of the study birds are also known, and samples have been collected for sexing, enabling information gathered from the loggers to be linked with information on intrinsic factors and possible demographic consequences.

Spatio-temporal mapping of the winter prey field (large zooplankton energy) will be obtained from the Continuous Plankton Recorder survey), and oceanographic variables (chlorophyll, eddy kinetic energy, sea surface height, mixed-layer depth, surface wind stress) from 3D model reanalyses (GLORYS, ERA5), for the non-breeding range of this population throughout the study period. These datasets will be used in conjunction with CMIP6 future ocean projections and a Random-Forest-based spatial projection of future large zooplankton energy developed by our Strathclyde collaborators, to hypothesize the likely effect of climate and ocean change on non-breeding-season movement and energy balance.

The ready availability of the long-term kittiwake and oceanographic datasets avoids potential risks of disruption to field data collection through issues including highly pathogenic avian influenza. However, the student, will have the opportunity to contribute to ongoing fieldwork on the Isle of May as part of the SEATRACK programme. Field work will involve catching, measuring and ringing breeding adults, deployment of geolocation-immersion loggers and recording of breeding success.

In addition to fieldwork skills, the student will learn how to use state-of-the-art methods for cleaning, processing, and analysing the collected biologging data and characterising migration routes and wintering areas. They will use cutting edge statistical methods to quantify between- and within-individual variation in a suite of movement metrics, and test for effects of environmental and intrinsic variables on movement, activity budgets, and energetics. They will also gain familiarity with the modelling of demographic data when estimating the relationship between non-breeding season movement characteristics and reproductive timing and success. Over and above gaining the above skills related to seabird ecology, the student will also develop experience in working with large empirical and modelled oceanographic datasets.

Year 1

Literature review and development of PhD plan; collation and processing of long-term bio-logging data from geolocation-immersion loggers; collation of oceanographic and prey datasets; contribution to field data collection (deployment of geolocation-immersion loggers) on the Isle of May, SE Scotland

Year 2

Training in statistical methods, e.g. movement modelling, mixed effects modelling, and structural equation modelling; contribution to field data collection as in Year 1; analyses for questions 1 and 2.

Year 3

Analyses for questions 3 and 4; thesis and paper writing; conference presentation

Year 3.5

Completion of thesis writing; preparation and submission of papers; conference presentation

The student will be based at UKCEH Edinburgh and will be co-supervised at the University of Glasgow, where they will be registered, with further training in the analysis of oceanographic and prey (zooplankton) data by collaborators at the University of Strathclyde.

They will develop skills in processing, visualisation and analysis of complex bio-logging and environmental (oceanographic) datasets using a range of advanced methods, including mixed effects modelling and structural equation modelling. Training will be provided by the supervisory team and by attending external specialised courses and workshops. The student will also develop fieldwork skills including deployment of bio-logging devices, bird handling and ringing, with training from the supervisory team and colleagues at UKCEH. Skills in scientific writing will be gained through preparation of thesis chapters and papers. Presentation and communication skills will be developed through participation in internal seminars, national and international conferences. Further training in transferable skills is available from all partner institutions and from Iapetus.

The student will also interact with researchers from the MASTS (Marine Alliance for Science and Technology for Scotland) working group on migration and prey energyscapes, as well as researchers from the SEATRACK programme including the ECR group within that (SEATRACK Fledglings), thus expanding their skills, research network and career development opportunities. They will be encouraged to drive the direction of their PhD project, supporting their development as an independent researcher.