 The breeding success of the American white ibis is sensitive to the hydrological conditions of the ecosystem such as rainfall and water levels . Low and decreasing water levels predict good prey accessibility . Water level reversals , where levels rise in the breeding season , disperse prey and impact on foraging success . Nest numbers and average clutch sizes are smaller in periods of reduced prey availability . The success rate of parents raising one or more young to 20 days of age ranges widely from 5 to 70 % of nests , and varies greatly between nearby colonies . American white ibis parents have been known to supplement their chicks ' diet with items such as cockroaches and rotting food from human garbage in poorer years , when fish and crayfish are more scarce . Studies have also shown that years with higher nesting numbers had significantly faster spring drying rates of water bodies than years with low nesting numbers . This is because faster drying rates means that there are fewer fish and increased available area where crayfish can be hunted . This highlights the fact that American white ibises do not use probability of nesting failure as a key factor in determining nesting sites but instead , rely on other criteria such as prey availability and nest @-@ site predation rates . The draining of wetlands in south Florida has also impacted on species that forage in shallow water such as the American white ibis , and its increase in numbers is a key indicator of restoration of habitat within the Everglades . 
