Energetics And Avian Behavior PDF Download

Avian divers are confronted with a number of physiological challenges when foraging in cold water, especially at depth. Diving is believed to be particularly costly in cormorants (Phalacrocoracidae) because of their poor insulation and less efficient foot-propulsion. I used open-circuit respirometry to study the energetic requirements of two Phalacrocorax species, the European shag (P. aristotelis) and the double-crested cormorant (P. auritus) when diving in a shallow (1 m) and deep (10 m) dive tank. I also investigated the modifying effects of water temperature and feeding status on dive costs. My results indicate that the energetic costs during shallow diving in European shags and double-crested cormorants are comparable to other foot-propelled divers. Metabolic rate was significantly increased when diving to greater depth and at lower water temperatures, while feeding before diving increased metabolic rate, albeit not significantly. The strong effects of depth and water temperature on cormorant diving metabolic rate are most likely a consequence of their partially wettable plumage and their reduced plumage air volume, which makes them prone to heat loss and, hence, increases thermoregulatory costs. The energetic requirements of animals have to be satisfied by intake of resources from the environment. Hence, the quest for food is a central aspect of animal behavior. Although the study of seabird foraging behaviour has greatly profited from recent technological developments, we still know little about predator-prey interactions on a fine scale. I used an underwater video array to investigate the prey-capture behaviour of double-crested cormorants foraging on live rainbow trout (Oncorhynchus mykiss). I tested the effects of a variety of factors on the underwater foraging behaviour of cormorants and established a functional link between prey density and cormorant prey capture rate. Prey density and behaviour both significantly affected predator performance. At prey densities below 2-3 g fish m-3 birds increased their search time during a trial drastically, while prey-encounter rate was greatly decreased. When cormorants attacked shoaling rather than solitary trout, their capture success was significantly reduced, while pursuit duration was significantly increased. Seabird energetics and behaviour are typically studied on the individual or species level. However, if we want to understand how seabirds react to environmental changes, we have to consider entire communities. In the western North Sea, a large seabird assemblage critically depends on a single fish species, the lesser sandeel (Ammodytes marinus), which is also exploited by an industrial fishery. I developed an algorithm to test for the capacity of four seabird species during chick-rearing in Scotland to buffer a potential decline in sandeel abundance by increasing their foraging effort in various ways. My results show that under the conditions currently operating in this region shags and guillemots (Uria aalge) may have sufficient time and energy to allow them to increase their foraging effort considerably, while Kittiwakes (Rissa tridactyla) and gannets (Morus bassanus) appear more constrained by time and energy respectively. My study suggests that during chick-rearing gannets are working at the highest metabolic level of all species considered and hence, have the least physiological capacity to increase foraging effort. This indicates that gannets could potentially be very sensitive to a reduction in sandeel abundance. My thesis emphasises the importance of taking into account seabird energetics as well as fine scale behavioural requirements, when trying to develop management schemes for fisheries that will allow the coexistence of both seabirds and human fishery in a sustainable way.