Yellow-legged gulls that nest in the Berlengas islands were formally kept in check by egg collection by local populations and limited food supply. However, since they started to forage in landfills in the mainland, with the protection of their nesting area by the creation of the Berlengas nature reserve, they became so abundant they were threatening the very island ecosystem. To prevent them from outcompeting other nesting marine birds, or destroying the delicate island endemic plants, some of their eggs are now injected with saltwater to make them inviable.