Patterns and mechanisms of seabird-environment interactions in southern Africa : population and individual studies

Abstract

The 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.