Estimating 30-year change in coastal old-growth habitat for a forest-nesting seabird in British Columbia, Canada

摘要

The marbled murrelet Brachyramphus marmoratus is an old-growth dependent species that nests in North American coastal forests. Canadian pop-ulations and occurrence data are limited; however con-cern over loss of nesting habitat in coastal British Columbia led to an assessment of 'threatened' by the Committee on the Status of Endangered Wildlife in Canada, and subsequent listing under the Canadian Species at Risk Act. Information on the availability and patterns of change in nesting habitat is essential for making land-use decisions and for monitoring the con-servation status of this wide-ranging seabird. We esti-mated potential marbled murrelet nesting habitat for the coast of British Columbia at 2 points in time, 1978 and 2008, and quantified habitat loss and modelled habitat recruitment over this 30 yr time period, a key time frame for the assessment of the conservation sta-tus of this high-profile species. We implemented 3 pre-dictive habitat suitability models for the province of British Columbia, ranging from exclusive to more inclusive models. Based on the intermediate habitat model scenario, including corrections using aspatial harvest records, we estimated that 20.6 to 24.2 % of potential marbled murrelet nesting habitat was lost to forest harvest and fire from 1978 to 2008. If modelled habitat recruitment is considered, then net change in potential nesting habitat is 18.5 to 22.2 % loss. Our esti-mates of potential murrelet habitat and subsequent habitat loss and chance are influenced by numerous sources of uncertainty, such as actual suitability of for-est stands for breeding murrelets and known deficien-cies in the forest harvest spatial datasets. However, the results presented here provide the first range of province-wide habitat change possibilities and are consistent with previous regional analyses of potential marbled murrelet habitat loss in British Columbia.