 Adult terns have few predators , but in Namibia immature birds are often robbed of their food by kelp gulls , and that species , along with Hartlaub 's gull , silver gull and sacred ibis , has been observed feeding on eggs or nestlings , especially when colonies are disturbed . Smaller <unk> with a relatively larger numbers of nests located on the perimeter are subject to more predation . In Australia , predation by cats and dogs , and occasional deaths by shooting or collisions with cars , wires or light @-@ towers have been documented . 
