Together with my colleagues at the University of Tartu, Estonia, we are looking for a highly motivated candidate for 4-year PhD funded project on the ecophysiology and behaviour of seabirds. You can see details of the project below. If interested, or if you have questions, do not hesitate to contact me and we can discuss about the project. It is highly recommended to contact me as soon as possible.
Supervisor(s): Jeffrey Carbillet, Jaanis Lodjak, Tuul Sepp
Duration: 4 years – From September 2024
Location: Tartu, Estonia, Institute of Ecology and Earth Sciences
Application deadline: 10th of May 2024
Contact: jeffreym@ut.ee
Seabirds are one of the world’s most endangered avian groups due to human-induced rapid environmental change, which is causing, among other things, a decline of suitable habitats. This decline increases the density of birds in the remaining suitable habitats, leading to a strong competition with conspecifics and representatives of other species that can reduce survival and reproductive success. Selection of a nesting site, which is crucial for improving the chances of a successful breeding event for a seabird, takes place at several spatial levels, starting from wider landscape scales and being finalised in a very small local scale of a few meters. Given that most seabirds are faithful to their breeding site, and the habitat loss is decreasing options for even the ones who would normally leave their colony of origin, small-scale nest location choice becomes increasingly more important. Within a breeding colony, habitat varies due to both landscape properties (micro-climate, vegetation, topography) and interactions with conspecifics and representatives of other species (social interactions, competition, predation), and this affects nest-site quality and reproductive output. While habitat modification and the use of low-quality nesting sites are known to reduce survival and reproduction in seabirds, the mechanisms through which these effects occur, and the potential for individuals to adapt through physiological and behavioural mechanisms remain unknown. Within this PhD project, we plan to use a longitudinal approach looking at nesting site selection in a colony of Common gulls (Larus canus) that has been monitored over the last 40 years, on an islet in the Matsalu National Park, in Western Estonia. The density of breeding Common gulls, but also other species has increased over the past decades, making it a perfect colony to study the factors affecting nesting site selection and its consequences on fitness. The aim of the project are 1) To determine the factors affecting nesting site selection, such as previous experience, genetic components, and behavioural profiles 2) To identify the mediators between environmental conditions around a nesting site and reproductive success, considering glucocorticoid hormones as a candidate, 3) To evaluate the consequences of nesting site selection on survival and reproduction, also considering the potential to adapt among years through life-history strategies adjustments.
Plan of the doctoral thesis (4 years), its innovativeness and importance to the development of the field of research:
Importance and innovativeness
Increased density of individuals reduces fitness in colonial seabirds that are facing high competition for resources and nesting sites (Miller et al., 2019). Habitat loss due to human-induced rapid environmental changes is currently decreasing nesting options, making nest location decision a key stage. While habitat modification and use of low-quality nesting site reduce survival and reproduction in seabirds (Pagenaud et al. 2022; Kokko et al. 2004), mechanisms through which these effects occur, and the potential for individuals to adapt through physiological and behavioural mechanisms remains unknown.
To fill this gap, we plan to use a longitudinal approach looking at nesting site selection in a colony of Common gulls (Larus canus) monitored over 40 years on an islet in the Matsalu National Park, where the density of individuals has increased over the past decades. Going beyond the classical biomarker-based approach, we plan to use a comprehensive, life-history strategy based approach, where a co-variation among physiological, behavioural and life history traits is considered (Réale et al., 2010). This allows to consider the potential to adapt to environmental conditions around the nesting site among years.
Workplan
1- Factors determining nesting site selection
The number of Common gull pairs breeding in the monitored colony has increased from 600 to more than 1000 over last decades. This might greatly impact selection of nest sites. We will combine a long-term multigenerational pedigree (~3000 individuals) with quantitative genetic studies to decompose variation in nesting site selection into genetic and permanent environmental mechanisms, using data on habitat composition around the nest, age, behavioural profiles (bold-shy gradient), and family relationships, to understand the factors influencing nesting site selection.
2- Density, competition, and parasite load
Seabirds are known to host parasites that can affect their fitness (Khan et al., 2019). Considering some nesting sites are located in areas with higher density of birds, competition for feeding and protect eggs from predation may be higher in these areas. A trade-off between the energy allocated to defend the nest and investment in immunity is expected (Sheldon & Verhulst, 1996), where birds facing higher competition should have a weaker immune system and be more susceptible to parasites. We plan to investigate this trade-off by linking nesting site location, density of birds, and parasite load to understand health consequences of nesting site location.
3- Hormonal processes to mediate nest site location and fitness
Glucocorticoid hormones are potential mediators between environmental conditions and life-history decisions (Dantzer & Swanson, 2017). Challenging environmental conditions are known to increase glucocorticoid levels in seabirds (Tartu et al., 2014). However, their potential as a signal for plastic adjustment of life history traits over a lifetime remains unexplored. We plan to link nesting site conditions (e.g. location, density of birds, habitat composition) and glucocorticoid levels of parents within years, to understand how nesting site conditions can affect the physiology of parents, but also among years, to look if a physiological adaptation can occur over time, shaping the life-history strategy of parents.
4- Effect of nesting site location on fitness
While nesting sites exposed to higher competition are usually expected to reach lower fitness than others, using a life-history strategy based approach will allow us to take into account the potential for individuals to adapt to their environmental conditions among-years. In this context, we could expect a gradient of nesting strategies ranging from fast individuals (bold, low glucocorticoids and high parasite load) in areas where the competition/density is higher, to slow individuals (shy, high glucocorticoids and low parasite load) in areas where the competition/density is lower.
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