 The American white ibis prefers to eat crayfish and other crustaceans , but also takes aquatic insects and small fish . Outside the nesting season , the diet is highly variable , as abundance and types of prey depend on the both region and habitat . In Los Llanos , located on the border of Columbia and Venezuela , the most frequent prey are insects , such as fly larvae and beetles . Generally in North America the main prey are crustaceans , mostly crayfish . In the Everglades and cypress swamps , the diet is primarily made up of crayfish , while those that feed in willow ponds eat predominantly fish . American white ibises that feed in mangrove swamps focus on crabs . The tactile nature of the ibis 's probing for food in mud means that it catches prey that are too slow to evade the ibis once located by its bill . In the Everglades , this means that crayfish make up a large part of the diet , but a more diverse array of invertebrates are taken in coastal areas . Although crayfish are sought by foraging ibises , prey switching to fish does occur if fish are found in great abundance . It is unclear whether the fish are more easily caught if overcrowded , or whether sheer numbers of fish mean that ibises are catching them instead of crayfish — normally , fish are more agile than crayfish and hence elude the ibis 's bill more easily . Fish are a more energy @-@ rich source of food for the American white ibis . In the breeding season , American white ibises in a colony at Pumpkinseed Island travelled further to forage in freshwater wetlands and catch crayfish , than nearby saltwater areas where fiddler crabs predominated , indicating their benefit was worth the extra energy expended in fetching them for their young . This travel results in the wholesale transport of nutrients across the landscape by the colony ; in a successful breeding year the colony at Pumpkinseed Island was estimated to have contributed a third as much phosphorus to the neighboring estuary as other environmental processes . 
