Native birds, mostly passerine species, ecologically associated with Culiseta melanura, the enzootic vector of eastern equine encephalomyelitis and Highlands J viruses in the eastern United States, were examined over a 12-year period in southeastern Massachusetts. These studies concentrated on those individual birds known, by banding returns, to be residents of large wooded swamps where both eastern equine encephalomyelitis and Highlands J viruses were known to be enzootic. Of 8,417 birds sampled, 1,227 (14.6%) were recaptured one or more times (mean 2.7 times). Antibody profiles on individuals nesting or feeding in enzootic areas were determined from serial blood samples drawn from these recaptured birds. The duration of detectable neutralizing antibody in these birds was found to be ephemeral in some species (e.g., black-capped chickadees) and extremely long-lasting in others (e.g., gray catbirds, swamp sparrows). The significance of these findings to arbovirus surveillance programs is discussed.