 This is an adaptable species that has learned to follow fishing boats for jettisoned bycatch , and to use unusual nest sites such as the roofs of buildings and artificial islands in salt pans and sewage works . Its eggs and young are taken by gulls and ibises , and human activities such as fishing , shooting and egg harvesting have caused local population declines . There are no global conservation concerns for this bird , which has a stable total population of more than 500 @,@ 000 individuals . 
