 Bird predators may seize anywhere from 7 % to 75 % of the progeny in a breeding colony . The fish crow ( Corvus ossifragus ) is common raider of American white ibis nests , accounting for up to 44 % of egg loss in a field study at Battery Island , North Carolina . Other predators of eggs and young include the boat @-@ tailed grackle ( <unk> major ) , black @-@ crowned night heron ( Nycticorax nycticorax ) , gulls , and possibly vultures , as well as the common opossum ( Didelphis marsupialis ) , raccoon ( Procyon lotor ) , and rat snakes ( <unk> species ) . Egg predation rates of the American white ibis decline with nest age owing to increased nest attentiveness by the parents , especially during the last week of incubation . High nest densities and reduced synchrony increase egg predation rates because of the increased opportunities afforded by the longer incubation times , as well as the greater availability of nests available for predation . 
