In Lithuania, common dormice Muscardinus avellanarius destroyed 6.6% of 3807 bird nests with eggs in nestboxes at two study sites. M. avellanarius occupied nests of pied flycatcher Ficedula hypoleuca without eggs or nests with incomplete clutches most often, ate unhatched eggs, but did not kill or bite nestlings and adult birds. M. avellanarius were very seldom found in nestboxes with nests of tits Parus spp. Edible dormice Glis glis destroyed 14.3% of 498 bird nests with eggs or nestlings at two study sites, mostly nests of F. hypoleuca and great tit Parus major. G. glis ate birds’ eggs, killed and ate nestlings and adult birds. Forest dormice Dryomys nitedula made the biggest impact on birds nesting in nestboxes. They destroyed 20.5% of 171 nests with eggs or nestlings, ate eggs, killed and ate nestlings and adult birds. The most common impact of D. nitedula on birds in nestboxes was the killing of adults, either breeding or just looking for nest sites, and F. hypoleuca made a majority among birds killed. F. hypoleuca was most affected by all three dormice species in Lithuania, while P. major was impacted less and only by G. glis and D. nitedula.