PARTICIPATION OF BIRDS (AVES) IN THE EMERGENCE OF LYME-DISEASE IN SOUTHERN MAINE

The contribution of migratory and resident birds to the introduction o f Lyme disease will vary with the degree to which various species expo se themselves to. and are infested by, juvenile vector ticks, and thei r ability to support and transmit the infectious agent. To examine the relative contribution of various passerine species during the emergen ce of this disease, we computed the abundance and infection rates of t he blacklegged tick, Ixodes scapularis Say. removed from mist-netted b irds with those from live-trapped mice st a coastal study site in sout hern Maine, collected during an 8-yr period in which the range of this tick and the incidence of Lyme disease increased in the state. Weekly bird-banding sessions using six le-m Japanese mist nets were carried out from May through August 1989-1996. In 1989, 1991, and 1993, mice w ere live-trapped in a Sherman trap grid (7 by 7 m) during five 3-night sessions, June through August; in 1994-1996, 2 such grids were simila rly trapped. Annual adult tick abundance was estimated by flagging veg etation. We removed 2,633 juvenile deer ticks from 1,713 of 1,972 bird s examined. Twenty-five of 64 bird species were infested. The percenta ges of birds infested and the rate of infection among removed larvae a nd nymphs increased over the years, but species varied markedly in the ir ability to infect ticks. No infected lan ae were removed from catbi rds or towhees. The larval to nymphal ratio was higher in mice than in birds. Infection rates among bird-derived larvae were less than among mice-derived larvae, but increased with time. Because of the differen t was in which individual species of passerine birds contribute to the availability of vector ticks and respond to the agent of Lyme disease in emerging areas, further research into host competency and borrelia cidal mechanisms is needed.