This data set includes the locations of all known seabird colonies along the coast of British Columbia, and provides a compilation of the population estimates of seabirds breeding at those colonies since 1980, and historical estimates prior to 1980 for some colonies. It does not include an estimate of the numbers of juvenile birds or non-breeders in the population.

The rationale for developing this inventory was the recognized need for a product that could assist with: coastal zone and conservation area planning; emergency response to environmental emergencies and identifying areas of potential interactions between seabirds and anthropogenic activities. In addition, the data used to develop the document provides a baseline to compare with future seabird population estimates in order to measure the impacts of shifts in composition, abundance and/or distribution of prey, and climatic and oceanographic changes. The database is not a substitute for on-site surveys usually required for environmental assessment.

Here we present data on the breeding colony population estimates of the 17 species of seabirds (including two storm petrels, three cormorants, one gull, and eight alcids) and one shorebird (Black Oystercatcher Haematopus bachmani) that breed on the coast of British Columbia. Over 5.5 million colonial birds are currently estimated to nest at 649 sites (Rodway et al. 2024). Five species (Cassin's Auklets Ptychoramphus aleuticus, Fork-tailed Storm-petrels (Hydrobates fucatus), Rhinoceros Auklets Cerorhinca monocerata, Ancient Murrelets Synthliboramphus antiquus, and Leach's Storm-petrels (Hydrobates leucorhous), comprise the vast majority of that population, although Black Oystercatchers (Haematopus bachmani), Pigeon Guillemots (Cepphus columba), and Glaucous-winged Gulls (Larus glaucescens), nest at the most sites. Marbled Murrelets (Brachyramphus marmoratus), which nest on the mossy limbs of mature and old-growth trees within the coastal forests, are not included in this database, due to their dispersed nesting habit.

The population estimates presented in this database are compiled from the results of several surveys. Many of the seabird breeding colonies in British Columbia have been known for more than 50 years, but because of the remoteness of the sites, visits to them have been rare. The majority of the data are the results of comprehensive inventories of colonial nesting seabirds along the British Columbia coastline conducted between 1974 and 1977 by the British Columbia Provincial Museum (BCPM; now Royal British Columbia Museum ) and between 1980 and 1989 by the Canadian Wildlife Service of Environment and Climate Change Canada (CWS). The goal of the BCPM surveys was to explore the entire BC coast to identify seabird nesting sites. Reliable, quantitative data were gathered on the breeding populations of all surface-nesting seabird species and rough estimates of population sizes were made for burrow-nesting species. The goal of the CWS survey program was to establish baseline estimates of breeding populations of burrow-nesting species in BC using standardized survey techniques to allow future comparisons and monitoring of those populations. During the 1980s, repeat surveys of surface-nesting species were also conducted by CWS in most regions of the BC coast. A few colonies on small remote islands were not visited during those surveys. Therefore, for some colonies the most current population estimates are from the first complete survey of the BC coastline, carried out by the Royal British Columbia Museum in the mid 1970’s.

Since 1989, surveys have been conducted by CWS on some alcid, cormorant and gull colonies along the BC coast, and results have been included in the dataset (data entry ongoing). As well as data from CWS surveys, we have attempted to obtain recent data from all other sources including Parks Canada, Transport Canada, the BC Ministry of Forests, Lands, Natural Resource Operations and Rural Development, the City of Vancouver, the Bamfield Marine Station, and the Laskeek Bay Conservation Society. Since 2000, inventories of nesting Black

Oystercatchers have been conducted in some regions of the coast by Parks Canada and partners (Gulf Islands National Park Reserve, Pacific Rim National Park Reserve, and Gwaii Haanas National Park Reserve) and results have been included in the dataset (data entry ongoing). A long time series of nesting Black Oystercatcher data collected by Laskeek Bay Conservation Society in the Laskeek Bay area of the East Coast of Moresby Island has also been included in this dataset.