Using air photos to interpret quality of Marbled Murrelet nesting habitat in south coastal British Columbia

Abstract

Reliable habitat assessment methods are needed to ensure the adequate management of Marbled Murrelet (Brachyramphus marmoratus) habitat in British Columbia. In two south coastal study regions, the Sunshine Coast and Clayoquot Sound, we evaluated the effectiveness of a qualitative habitat classification that uses air photo-interpreted forest structural characteristics for identifying and ranking habitat quality. Using a sample of 118 nest sites and 157 random sites within forests greater than 140 years old, we found that murrelets selected nest patches non-randomly with respect to forest characteristics. While selectivity varied between study regions, generally nest patches had taller and larger trees, exhibited more complex forest structure, and were located at lower meso-slope positions near large gaps or nearby edges. In addition, these patches were more often ranked higher in terms of habitat quality. However, we found that probable breeding success was greater in habitats classified as lower quality. Thus, further research is needed to understand our findings relative to other influences on breeding productivity, such as predators and hierarchal habitat selection. In summary, while our study supports the use of the current air photo habitat classification standards to improve identification and selection of murrelet nesting habitat for management, some modifications to these standards may be needed.