Our inventory of Prairie Warblers in Frontenac Provincial Park is now complete! Conducting the inventory required lots of hiking over rugged terrain and canoeing – 41 kilometres in all. The Prairies are occupying rock barren habitats in perhaps the most inaccessible part of the 5000 hectare park. I am relieved to report that it was well worth the effort as a surprisingly large number of Prairies were located. Prior to this season I had hopes that about ten pairs would be found in Frontenac but really had no expectations beyond the few pairs that were first encountered at Slide Lake last summer.
The second edition of the Ontario Breeding Bird Atlas provides an excellent summary of the current provincial status of the Prairie Warbler. Incidentally, a bright male Prairie Warbler was chosen as the cover bird for this important work. The authors of the account note that the distribution has remained unchanged since the first atlas conducted in the early 1980’s, although many long standing colonies had been deserted due to habitat succession. Several colonies in the Frontenac region have disappeared including a large population of perhaps 20 pairs that inhabited the west side of Canoe Lake, which hosted birds from 1961-1987. Another historical colony resided at Devil Lake for more than 40 years from 1948-1988 (Weir 2008). The largest population remaining in Ontario occurs in the Georgian Bay region where 270 pairs were located in the 1990’s (Harris 1998). Outside of Georgian Bay, colonies of Prairie Warblers seem to be less concentrated, possibly due to habitat shortage, which could make them more susceptible to extirpation.
Data from the second atlas suggest that away from the Georgian Bay area fewer than 50 pairs occur and the total provincial population is unlikely to exceed 320 breeding pairs. (Cadman et.al. 2007)
The population in Frontenac Provincial Park, inventoried for the first time this summer, includes a minimum of twenty territorial males! At least four of these males are paired with females. Additional males were likely encountered in two instances involving three males in territorial dispute but it was impossible to exclude potential overlap. The figure of 20 males is a conservative tally of birds with territories delineated by counter singing. I have yet to perform any analysis of habitat availability versus our coverage but strongly suspect that an upper limit of 30 pairs would be a reasonable estimate for the population. At 20-30 pairs It is quite possible that this population may be the largest known active colony outside of the Georgian Bay region.
I spent a lot of time looking for females and managed to find just four over several days of fieldwork in the rock barrens. Females were likely hunkered down on well hidden nests and not moving around much. I did find this female (pictured above) that was much more active. I watched her frequent comings and goings to a patch of dense shrub near an Eastern White Pine. She made half a dozen trips to the patch with beakfulls of “stuff”, either bugs or nest material. I didn’t approach the presumed nest site until the 7th trip when it was clear that food was being carried to the spot (approaching during nest building could have resulted in abandonment). I fully expected to find a nest with young in one of the shrubs but found this instead…..
This discovery of fledged young confirms successful breeding in Frontenac Provincial Park for this year and provides some indication that the colony is viable and productive! We now have a much better grasp on the current breeding status, habitat association and population density of Prairie Warbler in the park and can now begin setting more specific targets for future years. More to come in 2011….