Population status

Least Bittern
(Ixobrychus exilis)

Population trends for the Least Bittern in Canada are difficult to quantify. The species is concentrated in southern Ontario, a region well-covered by both the Great Lakes Marsh Monitoring Program and the Atlas of the Breeding Birds of Ontario but temporal coverage from the Marsh Monitoring only began in the mid-1990s, and the Atlas covers only the 20-year period between the mid-1980s and mid-2000s.  Results from both these programs point to a decline in abundance in recent years, as do data from the Quebec Marsh Monitoring Program (table below and Chapdelaine and Rail 2004), and anecdotal observations support historical decreases in breeding numbers across most of the species’ range (COSEWIC 2009c). Yet the species’ very low detectability, frequent turnover of breeding sites, and the possibility that Marsh Monitoring data may underestimate abundance, limits the accuracy of population trend estimates (Woodliffe 2007b, Poole et al. 2009). Extrapolating from available data, the species is perhaps best assessed as having shown a moderate decrease in population since 1970. However, the paucity of knowledge of this species’ biology, dynamic site selection and secretive nature have resulted in an absence of long-term trend estimates and thus this assessment is assigned low reliability.

 

Atlas of the Breeding Birds of Ontario

Additional information on: Atlas of the Breeding Birds of Ontario

Table 1: Population trends by geographic area
Geographic areaTime PeriodAnnual trend (%) Table 1 - footnote 1 Limits
LowerUpper
Ontario1981/85 - 2001/05-1.9-5.11.3
 

Picture of logo Great Lakes Marsh Monitoring Program

Additional information on: Great Lakes Marsh Monitoring Program

Table 2: Population trends by geographic area
Geographic areaTime PeriodAnnual trend Table 2 - footnote 1 Limits
LowerUpper
Great Lakes Basin in Ontario Select to view graph of the geographic area: Great Lakes Basin in Ontario 1995-2012; Great Lakes Marsh Monitoring Program1995-2012-1.2-3.61.2
 

Quebec Marsh Monitoring Program

Additional information on: Quebec Marsh Monitoring Program

Assessment date: 2013

Table 3: Population trends by geographic area
Geographic areaTime PeriodAnnual trend Table 3 - footnote 1 Limits
LowerUpper
Quebec Select to view graph of the geographic area: Quebec 2004-2013; Quebec Marsh Monitoring Program2004-2013-12.4-14.7-10.7
 

References