The milky stork breeds colonially in mangrove swamps, with breeding colonies ranging in size from 10–20 to a few hundred nests. In Java, breeding colonies of 75–100 nests have been estimated to cover 4.5 ha, with 5–8 nests per tree within colonies having been recorded. The height of the nest above the ground notably varies. Nests are commonly built in tall "Avicennia marina" and other "Avicennia" tree species in Java, and "Rhizosphora apiculata" trees in Sumatra, in both cases usually 6–14 m above ground, but sometimes in the very tops of trees. Nests on Pulau Rambut are built in tops of outstanding mangrove trees 30 m high. Similar nesting characteristics were observed on the island of Pulau Dua when the species still bred there. In Indonesia, some milky storks nest close to the ground in dense shrubs of "Acrostichum" mangrove ferns 2-6m above the ground. Milky storks also commonly nest in dead or dying mangrove trees. Further, some colonies in South Sumatra have been located far inland at brackish lakes or freshwater swamps in Alstonia trees reaching up to 60 m high.