UC Santa Cruz
The foraging ecology of seabirds in relation to contaminant exposure and oceanographic habitat
- Author(s): Gilmour, Morgan Elizabeth
- Advisor(s): Shaffer, Scott A
- et al.
The vastness of the ocean makes it difficult to study. This is compounded by regional differences in temperature, wind patterns, underwater topography, and primary productivity that extend from the ocean’s surface to depths of thousands of meters. Many organisms that inhabit the marine environment navigate many environmental changes as they move between regions in both the horizontal and vertical directions. The ability to navigate through different habitat types indicates that marine animals may be adaptable to multiple environments; however, it also suggests that they may be exposed to multiple hazards, including hazards of anthropogenic origin. Rates of anthropogenic inputs of chemicals and litter to the atmosphere and the ocean are increasing. However, many effects of anthropogenic compounds on marine life are only beginning to be understood. In this dissertation, I assessed foraging ecology, contaminants, and the effects of contaminants, in seabirds, which are unique among marine animals because they hunt for fishes and squid from the air, but breed on land. Land-based breeding enables them to be easily studied, and they are good samplers of the vast ocean because they travel tens to thousands of kilometers from the breeding colony to forage. I first tested the hypothesis that seabirds’ foraging behaviors are related to local oceanographic habitats, and that they exhibit behavioral plasticity to exploit the marine environment. GPS-tracking and remotely-sensed environmental data of four species of boobies (Sula spp.) demonstrated adaptable behaviors that changed depending on the type of oceanographic habitat in which boobies foraged (e.g. based on depth, sea surface temperature and topography). Second, I measured blood-based persistent organic pollutants (POP) and mercury contaminant concentrations in boobies and two species of frigatebirds (Fregata spp.) from four colonies in the Pacific Ocean and Caribbean Sea. I combined blood-based contaminant measurements with two measures of foraging ecology (blood-based stable isotopes and GPS-tracking). Boobies and frigatebirds were exposed to different contaminants depending on their foraging habitat (e.g. nearshore vs offshore). Though three of the study sites were remote and uninhabited, all birds had contaminants. Lastly, I tested the hypothesis that mercury would negatively affect seabirds’ breeding. I measured breeding in Flesh-footed Shearwaters (Ardenna carneipes) and Great-winged Petrels (Pterodroma macroptera) in the Southern Ocean (Western Australia). Though Great-winged Petrels’ blood mercury concentrations were the highest among all seabirds, I did not detect relationships between mercury and breeding in either species. Overall, seabirds are adaptive to their local marine environment. They traverse many habitat types while foraging, which influences the concentrations and types of contaminants that they encounter. However, they may be adapted, or tolerant, to some contaminants like mercury. Seabirds are good samplers of the marine environment, and continue to serve as good indicators of oceanographic processes and contaminants found in the ocean.