In a sample of 1,609 marked nests of five species of Ciconiiformes in 21 colonial nesting aggregations in the Everglades, evidence of abandonment without destruction of nest contents accounted for 31.3% of failures. In 66.9% of the failures, evidence at the nest suggested either predation resulting in nest failure or postabandonment scavenging of nest contents. In a sample of 106 nests isolated by a nonrepelling tracking medium, we found predation by snakes to account for 23% of nest failures; mammals accounted for an additional 20%. Failures due to these two categories accounted for 12% of the treated nests; abandonments may have been considerably underrepresented in this sample of nests. Mammalian predators rarely visited widely distributed baited tracking stations in the marsh, and we hypothesize that even 5-10 cm of water can substantially restrict travel by raccoons, foxes, and rats. Visitation by mammals to colonies occurred only when the water surrounding them receded, and was not related to the presence of alligators or distance from permanently dry land. We found little evidence of avian predation on wading bird nests, though birds readily scavenged abandoned nest contents. We discuss several attributes of the Everglades marshes which may limit access of predators to nesting colonies.