The species is uncommon in New Guinea and has suffered some declines due to mangrove clearances but is not considered threatened by the IUCN.

Where its range overlaps with that of the large-billed gerygone in the Kimberley it is actually displaced from the mangroves and is instead found in scrubland dominated by paperbarks and acacia.

The species feeds in the foliage of trees on insects, including beetles, grasshoppers, wasps, ants and moths.

It is less likely to catch prey in the air than other gerygones, but will join mixed-species feeding flocks with white-eyes, honey-eaters and fantails.

The mangrove gerygone breeds throughout the year, although principally in spring-summer in the east of Australia and during the dry season in the north.