Background information

Seabird Colony Monitoring Program

Environment and Climate Change Canada’s (ECCC) 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 Auklet, Rhinoceros Auklet, Northern Fulmar, Ancient Murrelet, Black-legged Kittiwake, Atlantic Puffin, Leach’s Storm-Petrel, Common Murre, Thick-billed Murre, gulls (several species), and terns (several species).

Population trajectories (the series of annual population estimates) were calculated using hierarchical Bayesian, generalized additive mixed models (GAMM). Monitoring seabird colonies is difficult, expensive, and sometimes dangerous field work; accessing colonies on remote coastal cliffs or islands, counting nest-burrows in dense coastal rainforest, or relying on safe flying weather to reach colonies on islands in the high-Arctic. As a result, it is generally not possible to monitor colonies every year, so statistical models must account for the sporadic nature of the survey data. The GAMMs used here provide smoothed time-series of annual population estimates (Ny), while accounting for the sporadic timing of annual surveys among and within colonies and the relative size of each colony (i.e. the largest colonies receive the most weight in the analysis). Population trends were calculated for long-term (as far back as 1970) and short-term (final 10 years) rates of population change. The trends were estimated as the geometric mean annual percent change between the population estimates (Ny) in the first and the final years of a particular time-series (e.g., for a 10-year trend between 2006 and 2016; (((N2016/N2006)(1/10))-1)*100). Long-term trends were calculated from 1970, or the earliest year in which data were available for a given species if data did not extend back to 1970. On the Atlantic coast, most long-term trends begin in 1970. On the Arctic coast, most trends begin in 1978, and on the Pacific coast, trends begin in 1984. A full description of the GAMM statistical methods used here is currently in preparation for publication in a scientific journal.

For colonies and species breeding on the Atlantic coast, the raw data for the GAMM consisted of complete counts of all breeding pairs at the colony (Rail and Cotter 2007, Gaston et al. 2009). For the Arctic coast, the raw data were indices of relative numbers of breeding pairs observed at the colony, derived from counts conducted by ECCC researchers (Gaston 2002, Gaston et al. 2009). For the Pacific coast, where the monitored species nest in burrows, the raw data were counts of burrows, conducted within multiple permanent monitoring plots located in each of the monitored colonies (Rodway and Lemon 2011).


  • 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. & Lemon, M.J.F. 2011. Use of permanent plots to monitor trends in burrow-nesting seabird populations in British Columbia. Marine Ornithology 39: 243-253.