Population status

Common Tern
(Sterna hirundo)

Dedicated monitoring information is available from tern colonies in Atlantic Canada, Quebec, the Great Lakes, and the Northwest Territories. Results from surveys in the Great Lakes suggest substantial decreases in abundance; the population in Canadian waters and connecting channels has declined by more than 40% since about 1970, from a high of 16,000 nests (Courtney and Blokpoel 1983, Morris et al. 2010; see also graph below). Trends elsewhere in the range are variable (Morris et al. 2012). In 2012, surveys of the large lakes of central Manitoba (Lakes Winnipeg, Winnipegosis and Manitoba) were conducted; abundance of Common Tern was found to have increased relative the 1970s but showed a 57-67% decline in the population over the last 20 years (Wilson et al. 2014). These data help fill an important gap in central/western Canada and suggest that declines are not restricted to the Great Lakes. Breeding Bird Survey results suggest little change in the abundance of Common Terns in Canada relative to about 1970, though this survey is not ideally suited to monitoring this colonial, island nesting species. Overall, the abundance of Common Terns in Canada has most likely shown little overall change since about 1970, but the population appears to be experiencing a decline in the last decades.

Great Lakes Decadal Colonial Waterbird Census

Additional information on: Great Lakes Decadal Colonial Waterbird Census

View numerical data of the graph.

Breeding Bird Survey (BBS) - Canadian analysis

Additional information on: Breeding Bird Survey (BBS) - Canadian analysis

View definitions of table column headings being used by: Breeding Bird Survey (BBS) - Canadian analysis

Table 1: Population trends by geographic area
Geographic area	Time Period ^{Table 1 - footnote 1}	Annual trend ^{Table 1 - footnote 2}	Intervals ^{Table 1 - footnote3}
Geographic area	Time Period ^{Table 1 - footnote 1}	Annual trend ^{Table 1 - footnote 2}	Lower	Upper
Canada Select to view graph of the geographic area: Canada 1970-2012; Breeding Bird Survey (BBS) - Canadian analysis	1970-2012	-0.5	-4.6	4.6

References

Courtney, P.A and H. Blokpoel. 1983. Distribution and numbers of Common Terns on the lower Great Lakes during 1900-1980: A review. Colonial Waterbirds 6:107-120.
Gaston, A.J., D.F. Bertram, A.W. Boyne, J.W. Chardine, G. Davoren, A.W. Diamond, A. Hedd, W.A. Montevecchi, J.M. Hipfner, M.J.F. Lemon, M.L. Mallory, J.-F. Rail and G.J. Robertson. 2009. Changes in Canadian seabird populations and ecology since 1970 in relation to changes in oceanography and food webs. Environmental Reviews 17:267-286.
Morris, R.D., C. Pekarik and D.J. Moore. 2012. Current status and abundance trends of Common Terns breeding at known coastal and inland nesting regions in Canada. Waterbirds 35: 194-207.
Morris, R.D., D.V. Weseloh, F.J. Cuthbert, C. Pekarik, L.R. Wires and L. Harper. 2010. Distribution and abundance of nesting Common and Caspian Terns on the North American Great Lakes, 1976 to 1999. Journal of Great Lakes Research 36:44-56.
Wilson, S., R. Bazin, W. Calvert, T.J. Doyle, S.D. Earsom, S.A. Oswald, and J.M. Arnold. 2014. Abundance and trends of colonial waterbirds on the Large Lakes of Southern Manitoba. Waterbirds 37(3):233-244. Wilson, S., R. Bazin, W. Calvert, T.J. Doyle, S.D. Earsom, S.A. Oswald, and J.M. Arnold. 2014. Abundance and trends of colonial waterbirds on the Large Lakes of Southern Manitoba. Waterbirds 37(3):233-244. (Link)