Current Status and Abundance Trends of Common Terns Breeding at Known Coastal and Inland Nesting Regions in Canada

Distribution and abundance of nesting common and Caspian terns on the North American Great Lakes, 1976 to 1999

“…Common Tern numbers also appear to have peaked in the early 1990s at between 15,140 and 19,997 pairs not including Lake Winnipegosis (Manitoba Conservation, unpubl. data), although higher numbers have been reported (Morris et al 2012). Common Tern abundance then decreased to the nearly 6,568 pairs estimated in 2012 in the same region, a 57-67% decline in 20 years.…”

“…Common Tern abundance then decreased to the nearly 6,568 pairs estimated in 2012 in the same region, a 57-67% decline in 20 years. This trend is considerably more rapid than that observed for Common Terns in the Canadian Great Lakes (-41%, 1976-2009) where declines are of conservation concern (Morris et al 2010(Morris et al , 2012 and suggest a need to revise the conclusions in Morris et al (2012) regarding listing of this species only in Ontario.…”

“…Ground counts typically have low error (4-22% ;Hutchinson 1979;Erwin 1980) and are usually based on nests, thus providing a more direct link to the number of breeding pairs at a colony. Adult counts are reliable from the air, but estimates of nests or incubating adults are less accurate, yielding estimates that differ from ground counts by up to 35% or more (Kadlec and Drury 1968;Morris et al 2012). Both overestimation (Green et al 2008) and underestimation (Rodgers et al 2005) of colony size have been reported for visual counts from fixed-wing aircraft (Erwin 1982;Rodgers et al 2005).…”

“…On the Great Lakes, Herring Gull abundance increased from the late 1970s to the late 1980s and then declined to the late 1990s (Morris et al 2003). Common Tern numbers have generally increased since the 1970s (Nisbet 2002), but with recent declines in the Canadian portion of the Great Lakes (Morris et al 2012) and the mid-Atlantic coast (Brinker et al 2007). Herring Gulls and Common Terns are also common breeders across the boreal forest where survey coverage is limiting (Stelfox and Brewster 1979;Pierotti and Good 1994;Nisbet 2002;Wilson 2013), and it is not clear how their abundance or distribution has changed across this portion of their range.…”

“…Double-crested Cormorants and Ring-billed Gulls are abundant in many regions and they may be actively managed, particularly where they are viewed as competing with fisheries in the case of Doublecrested Cormorants or where they create problems in urban areas or near airports (Wires and Cuthbert 2006; U.S. Fish and Wildlife Service 2009;Pollet et al 2012). In contrast, Common Terns are declining in some regions such as the Great Lakes, prompting conservation concern (Morris et al 2012). These variable patterns highlight the importance of updated survey information from key breeding areas that do not receive regular monitoring but are essential for proper assessments of regional and continental abundance and trends.…”