||Within the socially monogamous systems of most songbirds, extrapair copulations (EPCs) are common as part of a mixed mating strategy. However, the genetic mating system of Boreal Chickadees ( Poecile hudsonicus ) has not been examined. In the summers of 2007-08, I installed artificial nests snags, recorded breeding phenology, and collected blood samples at two field sites in Nova Scotia. I employed three microsatellite DNA markers to test for extrapair paternity (EPP). Five out of seven nests (71%) had at least one extrapair offspring; this is among the highest reported EPP rates in the Paridae to date. Nest monitoring revealed the first accounts of Boreal Chickadees rearing multiple successful broods, with a long breeding season extending from early May to late August. As the Boreal Chickadee and other brown-capped chickadees lack a broadcast song, future studies will be crucial in determining whether high EPP is shared by species that do not sing.