Population increase in Kirtland’s warbler and summer range expansion to Wisconsin and Michigan’s Upper Peninsula, USA

The threatened Kirtland’s warbler Dendroica 25 pairs and at least nine nests fledged young. One male ringed as a fledgling returned to breed in two subsequent kirtlandii breeds in stands of young jack pine Pinus banksiana growing on well-drained soils in Michigan, years. After a 19-year period of population stability, the Kirtland’s warbler population increased four-fold during USA. We summarize information documenting the range expansion of Kirtland’s warbler due to increased habitat 1990–2000, most likely in response to a tripling in habitat area. This increase in sightings and documented breedmanagement in the core breeding range in the Lower Peninsula of Michigan during 1990–2000. We collected ing may be related to habitat availability in Michigan’s Upper Peninsula and to saturation of habitat in the main records and conducted searches for the species in Michigan’s Upper Peninsula and Wisconsin over 1978– breeding range. The increase in extra-limital records during 1995–1999 corresponds to the time when the 2000. During that time 25 males were found in Wisconsin and 90 males in the Upper Peninsula. We documented population went from the minimum to the maximum projected population densities, and a decline in natural colonization of Michigan’s Upper Peninsula by six ringed males from the Lower Peninsula of Michigan. Four ringed wildfire habitat was just oCset by new managed habitat for the Kirtland’s warbler. birds also moved back to the core breeding range, including two males that made two-way movements between the core breeding range and the Upper Peninsula. Thirty