 In South Africa , this species has adapted to breeding on the roofs of building , sometimes with Hartlaub 's gull , which also shares the more typical nesting sites of the nominate race . In 2000 , 7 @.@ 5 % of the population of this subspecies bred on roofs . Artificial islands in salt pans and sewage works have also recently been colonised by this adaptable seabird . 
