It is a very interesting study. I also observed ant nests in a breeding colony of Caspian Gulls Larus cachinans in Poland (Europe). Ants built nests under/within nests of Caspian Gulls. They belonged to genus Myrmica and Formica. However, I did not observe aggressive behaviour towards chicks probably because these ants foraged on fish brought by parents for chicks. I observed numerous fish at gull nests and ants swarmed at fish. Thus, it seems they competed with gull chicks for food. However, breeding success was high in a colony with only few unsuccessful pairs.