Fig 2.

(a) total observed costs associated with alien birds incurred at mainland or island locations; (b) proportion of different types of observed costs incurred at mainland or island locations. Costs at mainland locations are shown with and without costs for street pigeons Columba livia forma urbana. ‘Mixed’ = combined ‘damage’ and ‘management’ costs (where information was insufficient to separate them). All costs for street pigeons were categorised as ‘mixed’. ‘Damage mixed’ = combined ‘damage to agriculture’, and ‘damage other’ costs (where information was insufficient to separate them).