Background information

Analysis of Seabird Colony Counts

Environment Canada’s Canadian Wildlife Service has organized colonial seabird monitoring since the mid-1960s on all three coasts (East, West and Arctic). Breeding colonies of the following species have been monitored, using field methods suited to each species: Cassin’s and Rhinoceros auklets, murres (2 species), Northern Fulmars, Ancient Murrelets, gulls (several species), Black-legged Kittiwakes, Atlantic Puffins, storm-petrels (2 species) and terns (several species).

Trends were calculated for each colony that has been repeatedly surveyed since 1970. These colony-trends were estimated by fitting a line to the log of the annual counts, for colonies surveyed three or more times; and for colonies surveyed only twice, by calculating the average (geometric) annual percent change between the two surveys. National and regional trends for each species were calculated by averaging colony-trends across all colonies. The reported, overall trends represent the weighted geometric average annual percent change across all colonies, weighted by the size of the colony (maximum recorded colony count) and the length of time between the first and most recent surveys (total time span of monitoring at the colony). The weighting ensures that the overall population trends primarily reflect the longest term trends from the largest portions of the species’ population. The standard errors of the overall trend estimates are derived from the observed variation in trends among the monitored colonies.

For additional information, see Rodway (1991), Gaston (2002), Rail and Cotter (2007) and Gaston et al. (2009).

References

  • Gaston, A.J. 2002. Results of monitoring Thick-billed Murre populations in the Eastern Canadian Arctic, 1976-2000. CWS Occasional Paper No. 106:13-50.
  • Gaston, A.J., Bertram, D.F., Boyne, A.W., Chardine, J.C., Davoren, G., Hedd, A., Hipfner, J.M., Lemon, M.J.F., Mallory, M.L., Montevecchi, W.A., Rail, J.F. and Robertson, G.W. 2009. Changes in Canadian seabird populations and ecology since 1970 in relation to changes in oceanography and food webs. Environmental Reviews 17:267-286.
  • Rail J.F., Cotter R. 2007. Sixteenth Census of Seabird Populations in the Sanctuaries of the North Shore of the Gulf of St. Lawrence. Canadian Field-Naturalist 121:287-294.
  • Rodway, M.S. 1991. Status and conservation of breeding seabirds in British Columbia. pp. 43-102 In: Supplement to the Status and Conservation of the World’s Seabirds. J.P. Croxall (Ed.), International Council for Bird Preservation, Cambridge, UK.