Models of Ashmole's Halo

Ashmole's halo is an area of reduced food availability around a colony of seabirds caused by the feeding behaviour of the birds. A model of the halo based on time and energy budgets has been used to predict how the intake rate of a colony member depends on distance from the colony. On this basis, the density of seabirds as a function of distance is predicted. This relationship is then used to relate colony size to foraging range. In this paper, I give a critical review of this work. The validity of this approach is of more than academic interest because it is being used to assess the consequences of changes to the environment on seabird populations. I compare the approach to an alternative that includes the dynamics of the prey and make suggestions for future lines of research.