How animals distribute themselves in space: changing energy landscapes
Final Report Abstract
The foraging efficiency of animals determines whether they will be able to raise healthy broods, maintain their own condition, avoid predators and ultimately increase their fitness. Most studies of the foraging behaviour of animals have concentrated on the description of movements. However, the mechanisms underlying animal foraging behaviour remain mostly unexplained. Recent advances in animal movement tracking and data analyses have a great potential to fill this gap in our knowledge. With the use of accelerometers and GPS loggers, features of the habitat and the way animals deal with variable conditions can be translated into energetic costs of movement, which, in turn, can be viewed as energy landscapes (or energy-scapes). In this study, I took advantage of the newly available technology and methods in order to reveal the underlying mechanisms of animal foraging, using Gentoo Penguins from the Falkland / Malvinas Islands as a model species known for their flexibility in foraging behaviour. The results suggest that the marine areas used by Gentoo Penguins varied among years, as well as the degree of spatial segregation between colonies. Gentoo Penguins preferentially used the areas of the energy landscape that resulted in lower foraging costs The selection of the foraging areas made by Gentoo Penguins varied noticeably in space and water depth, but in all cases implied minimal power requirements compared with other parts of the for the penguins reachable landscape around the colony. The energy landscapes varied in time and between the colonies with the highest costs observed for the South End colony in 2013-4. This probably resembles the interaction between foraging effort and oceanographic conditions, a possibility that I am exploring through current additional analyses. Birds from the South End colony carried out more pelagic dives in 2013-4, while the proportion of pelagic and benthic dives was almost equal for both colonies in 2014-5. The stable isotope analyses revealed a a higher trophic level and more pelagic or offshore foraging during 2014-15. The larger isotope niches in the breeding season 2013-14 implies that the individuals had to specialise in their prey choice while the small niches in 2014-15 suggest that some prey was available in large quantities and served as a food base for most birds. All in all, these results confirm previous hypotheses that energy landscapes vary in time and that the seabirds forage in areas of the energy landscapes that result in minimized energetic costs. This in turn supports the view of energy landscapes as a mechanism underlying foraging behaviour.
