It is difficult to quantify the national trend for Least Bittern, even though the population is concentrated in southern Ontario which is well covered by both the Breeding Bird Survey (BBS) and the Great Lakes Marsh Monitoring Program (MMP). Only the BBS covers the full range of the species, and it indicates a 23% increase since 1970. However, since 1995 the MMP trends for the Lake Ontario and the Lake Huron and Michigan watersheds show moderate increases of 39 to 69%, and there has been a large increase of 138% in the Lake Erie watershed. The increases were likely due, at least in part, to increasing Great Lakes water levels, which increase breeding habitat quality for this species in Great Lakes coastal wetlands (Tozer et al., 2024). In Quebec, the MMP only dates back to 2004 and shows little change.

The second breeding bird atlases in Quebec (Atlas of the Breeding Birds of Quebec, 2017) and the Maritimes (Makepeace, 2015) both showed more squares recording the species than the first atlases 20 years earlier. Interestingly, all but two sites where Least Bittern was observed were different between the first and second Maritimes atlas (Makepeace, 2015), underscoring the difficulty of monitoring this species given its dynamic site selection. The overall evidence suggests that the Canadian population has at least maintained its abundance, and has likely increased in at least some regions.

The population goal for Least Bittern is to maintain and, where possible, increase its population size and area of occupancy in Canada. This goal is defined in the Recovery Strategy for Least Bittern under the Species at Risk Act. Recent monitoring data suggest that Least Bittern is within its goal range.