Relative Abundance and Habitat Associations of Least Bitterns at Long Point, Lake Erie

Primary Investigator:
Nick Bartok, M.Sc. Graduate

Dr. Scott Petrie, Long Point Waterfowl Executive Director
Dr. Hugh Henry, University of Western Ontario
Dr. Michael Schummer, Long Point Waterfowl Scientist


The Least Bittern is listed as a threatened species in Canada and Ontario.  The Canadian population of Least Bitterns occurs mainly within southern Manitoba, Ontario and Quebec and has been estimated at 1500 breeding pairs.  Recent survey results from the Breeding Bird Survey and Marsh Monitoring Program suggests a decrease in the abundance of Least Bitterns, but adequacy of these surveys is questionable because methods do not properly survey Least Bittern habitat.

Project Description

Nick estimated relative abundance of Least Bitterns in palustrine wetlands at Long Point, Lake Erie, Ontario May – July 2008 and 2009.  Nick (and his technicians) conducted 1459 call-broadcast point
counts, using the National Least Bittern Survey Protocol, within approximately 3500 ha of federal, provincial and private wetlands.  In 2008 (n = 193 survey stations), 272 Least Bittern detections were recorded of which 96 were estimated to be unique (0.49 birds/ survey station), whereas in 2009 (n = 351 survey stations) 712 detections were recorded and estimated as 197 unique Least Bitterns (0.56 birds / survey station).   Based on detections of  Least Bitterns responding to the survey protocol with the ‘Coo’ call (n = 118) in 2009, wetland area not surveyed, and total area of coastal wetland, Nick estimates 195 pairs of Least Bitterns at Long Point, Lake Erie and 1434 pairs in coastal wetlands of the Canadian Lower Great Lakes.  Thus, the breeding population of Least Bitterns in Canada (n = 1500) is potentially biased low.  Use of the National Least Bittern Survey Protocol should be continued and expanded to increase our understanding of Least Bittern distribution, relative abundance, and habitat use for effective wetland management and species-listing policy.

Little is known about specific habitat variables that influence site selection of Least Bitterns, particularly in Ontario.  Point counts, macrohabitat, and microhabitat assessment methods were used to determine relative abundance and habitat selection of Least Bitterns in wetlands at Long Point, Lake Erie, Ontario.  Nick measured macrohabitat variables using percent cover of vegetation at 344 survey stations with a 50 m radius circular plot and conducted 211 microhabitat habitat assessments using quadrats.  Nick also assessed the relationship between relative abundance, interspersion, and macrohabitat variables (n = 11).  Macrohabitat assessments determined percent cover of Cattail and Bulrush to be the best predictors of Least Bittern presence.  It was less likely to find a presence of Least Bitterns as the percent cover of Phragmites, trees / shrubs, and grass / sedge increased.  Microhabitat assessments determined the number of dead cattail stems as the best predictor of Least Bittern presence.  Interspersion of the designated study sites (n = 12) was not found to influence relative abundance of Least Bitterns at the wetland scale.   Interspersion and percent cover of Cattail and Bulrush influenced relative abundance of Least Bitterns at the survey station scale.  Nick recommends managing wetlands to increase the amount of Cattail and interspersion.

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