Patterns and mechanisms of seabird-environment interactions in southern Africa : population and individual studies
Appears in the following Collection
- Biologisk institutt 
AbstractThe interactions between seabirds and their environment, notably their prey, include complex spatial patterns and mechanisms that span over different scales of processes (e.g. physiology, behaviour, population). To understand large-scale patterns in seabird populations it is necessary to develop insight in the respective fields of study of physiology, behaviour and population ecology, and to reconcile these levels. Working along this line of research, I propose in this thesis to appreciate seabird-environment relationships from different perspectives: at the level of the population and of the individual. The first part of the thesis investigates whether regional trends of South African seabird populations (African penguin, Cape gannet, Cape cormorant and swift tern) follow a major shift in the distribution of their prey [Paper 1]. I demonstrate that for these seabirds the breeding populations respond at the level of the colony to the spatio-temporal variability of their prey, and I propose potential mechanisms for such responses [Paper 2]. The second part is dedicated to the analysis of patterns in prey distribution and individual seabird movements in relation to oceanographic mesoscale features such as fronts. I evidence that frontal structures are predictable areas where to find prey [Paper 3] and that seabirds like Cape gannets adjust their foraging strategies to such structures in order to optimize their foraging success [Papers 4 and 5]. This thesis underlines the importance of the spatial dimension in the relationships between seabirds and their prey, and highlights the importance of oceanographic features as catalysts of seabird-prey interactions. LIST OF THE PAPERS
PAPER 1: Crawford R.J.M., Sabarros P.S., Fairweather T., Underhill L.G. & Wolfaardt A.C.(2008) Implications for seabirds off South Africa of a long-term change in the distribution of sardine. African Journal of Marine Science, 30(1):177-184, 2008.
PAPER 2: Sabarros P.S., Durant J.M., Grémillet D., Crawford R.J.M. & Stenseth N.C. (in revision) Differential responses of three marine top-predators to spatio-temporal variability of shared resource. Marine Ecology Progress Series
PAPER 3: Sabarros P.S., Ménard F., Lévénez J.-J., Tew-Kai E. & Ternon J.-F. (2009) Mesoscale eddies influence distribution and aggregation patterns of micronekton in the Mozambique Channel. Marine Ecology Progress Series, 395:101-10, 2009.
PAPER 4: Sabarros P.S., Grémillet D., Stenseth N.C., Ryan P.G. & Machu E. (in revision) A critical assessment of methods to study area-restricted search in seabirds using Cape gannets. Methods in Ecology and Evolution
PAPER 5: Sabarros P.S., Grémillet D., Demarcq H., Moseley C., Mullers R.H.E., Pichegru L., Stenseth N.C. & Machu E. (submitted) Fine-scale recognition and use of submesoscale fronts by Cape gannets in the southern Benguela region. Marine Ecology Progress Series