| Abstract |
For many polar species, climate change is likely to result in range contractions and negative population trends. For those species whose distribution is limited by sea ice and cold water, however, polar warming could result in population increases and range expansion. Population increases of great cormorants Phalacrocorax carbo in Greenland are associated with warmer sea surface temperatures, but the actual impact of environmental change on cormorant spatial ecology remains unclear. In the present study, we investigate how Arctic warming is likely to influence the distribution of cormorants in Greenland. Using geolocation data, we show that many individuals that breed above the Arctic Circle migrate south and winter at lower latitude. We then couple estimates of migratory flight costs with a model that predicts daily energy expenditure during winter on the basis of water temperature, ambient illumination during diving, dive depth and day length. This model shows that the most energy efficient strategy predicted for any breeding location is to migrate as far south as possible, and that, for a given wintering location, it is more energetically expensive to breed at high latitude. We argue that cormorants currently undertake a winter migration to escape the polar night and reduce winter energy costs and that their wintering grounds in Greenland will remain largely unchanged under Arctic warming. This is because low levels of ambient illumination during the polar night will continue to restrict foraging opportunities at high latitude during winter. Northward expansion of the breeding range will result in increased energy expenditure associated with long migratory flights, and the cost of such flights may ultimately limit the breeding range of cormorants. Such limitations are likely to represent a general constraint on the capacity of visually guided predators to respond to climate warming, and may limit the predicted poleward range shifts of these species. |
