Population status

Caspian Tern
(Hydroprogne caspia)

Dedicated waterbird surveys that target individual colonies provide the best monitoring data for the Caspian Tern, although coverage of colonies is incomplete. Surveys throughout the Great Lakes have documented moderate increases in abundance overall (see graph below), and large increases in some areas. For example, 47 nests were estimated to be present in Lake Ontario in the late 1970s as compared to 1,541 nests in 2009 (C. Weseloh et al., unpublished data). Increases were also observed at what are perhaps Canada's largest colonies, in Lakes Winnipeg and Winnipegosis (Cuthbert and Wires 1999). In 2012, all colonies on the large lakes in southern Manitoba were surveyed. The survey revealed evidence of a long-term increase since the 1970s, but with an indication of a decline since the 1990s (Wilson et al. 2014). The small Atlantic coast population may be experiencing a decline (Wires and Cuthbert 2000) and the species has been listed as threatened in Québec since 2009. Results from the Breeding Bird Survey (BBS) suggest little overall change in abundance in Canada relative to about 1970 but, even in regions well covered by the BBS, colonies may be poorly monitored by this roadside survey because the largest colonies tend to be in the middle of large lakes. However, BBS results provide corroboration that the population within Canada is not decreasing. Considering all information from these various surveys, Caspian Terns appear to have shown a moderate increase in abundance in Canada since about 1970, but incomplete information from prairie colonies means that this assessment is of moderate reliability.

 

Great Lakes Decadal Colonial Waterbird Census

Additional information on: Great Lakes Decadal Colonial Waterbird Census

Trend of number of nests observed

View numerical data of the graph.

Breeding Bird Survey (BBS) - Canadian analysis

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

Table 1: Population trends by geographic area
Geographic areaTime Period Table 1 - footnote 1 Annual trend Table 1 - footnote 2 Intervals Table 1 - footnote3
LowerUpper
Canada Select to view graph of the geographic area: Canada 1970-2012; Breeding Bird Survey (BBS) - Canadian analysis1970-20120.5-7.26.9
 

References