Data on the Forster’s Tern are available from several surveys, but the species is not well monitored by any of them. Christmas Bird Count data cover only a small portion of the species' wintering range; most birds winter farther south, so the survey is not considered here. The Breeding Bird Survey (BBS) is not ideally suited to tracking colonial waterbirds, therefore sample sizes and precision of the trend estimates are low in Canada. BBS results at the continental scale suggest a moderate decrease in abundance since 1970, with moderate precision, but these results mostly represent the larger population in the United States, and have a very high degree of regional variability (A. Smith, CWS, pers. comm.). Finally, the Great Lakes Marsh Monitoring Program suggests little overall change despite large fluctuations, but provides no insight into the majority of Canadian birds that breed in the prairies. Both the Alberta and Ontario breeding bird atlases, the only two atlases within the species' range that have been repeated, suggest high turnover among specific breeding locations with little change in overall distribution since the 1980s (Semenchuk 2007, Weseloh 2007), but breeding records are too few to reliably infer temporal trends. With a tendency to nest on vegetation in deep water and to alternate among ephemeral colony sites (McNicholl et al. 2001), this species would be best monitored by programs targeting colonial marsh birds. Current data are insufficient to allow for an assessment of the national population status relative to 1970. Because the species is considered to be data deficient, a national population goal has not yet been determined.
Additional information on: Breeding Bird Survey (BBS) - Canadian analysis
Additional information on: Great Lakes Marsh Monitoring Program
