The environmental impact assessments of most offshore windfarm proposals raise the potential effects on birds as an important issue. Offshore windfarms may affect birds in a number of different ways including mortality due to direct collisions of birds while in flight and mortality induced by habitat loss due to the avoidance by foraging birds of such conspicuous structures. Birds that may be affected by displacement from foraging areas within close proximity to windfarms are likely to be those such as common scoter and common eiders that feed on sedentary or slow-moving bottom-dwelling organisms such as bivalve molluscs and fish-eating birds such as grebes, terns, auks and divers. This present study used field observations and surveys combined with an individuals-based modelling approach to predict the change in over-winter mortality rates of common scoter that would result from the displacement of birds from potential feeding habitat through the avoidance of windfarms in Liverpool Bay. The model code is, however, not specific to Liverpool Bay and can be utilised for other areas provided that suitable data are collected.