Concern about increasing numbers of Black backed gulls

I am concerned about the increasing numbers of black-backed gulls and the impact that they are having on a wide range of native birds through direct predation, disturbance and klepto-parasitism.

Photogarph shows attempted klepto-parasitism of a adult Caspian tern by a juvenile Black-backed gull at Avon-Heathcote estuary - august 2010