Manley, Irene A.

Marbled Murrelets (Brachyramphus marmoratus) nest predominantly in the canopies of large old-growth conifers, and are listed as Threatened in Canada and 3 US states mainly as a consequence of reductions in this habitat due to logging. We assessed the re-use of nest sites (nest trees) by murrelets in British Columbia using 3 types of data: 1) evidence of return of adults to the same nest site; 2) evidence of multiple nests within the same tree; and 3) re-checking known nest trees in subsequent seasons for evidence of re-use. All 3 methods showed evidence of re-use of nest trees in different years, but there were marked regional differences in the degree of re-use. Re-use of nest trees was most frequent in regions with extensive loss of nesting habitat due to logging (Southern Mainland Coast and East Vancouver Island), and rare in a less disturbed region (West Vancouver Island). Overall, 26 of 143 (18%) nest trees climbed showed evidence of multiple nesting in separate seasons. Management of nesting habitat should incorporate these results by providing greater protection of habitat in regions where habitat is sparse, and by minimizing predation risk where murrelets more frequently re-use nest sites. Since re-use of nest sites is infrequent, managers should aim to provide murrelets with multiple choices for nest sites, such as maintaining large tracts of old-growth forest with many large trees containing potential nest platforms.

Nest platforms (mossy pads, limbs, and deformities >15 cm in diameter) are key requirements in the forest nesting habitat of the threatened Marbled Murrelet (Brachyramphus marmoratus (J.F. Gmelin, 1789)). Little is known about factors that affect the availability of platforms or the growth of canopy epiphytes that provide platforms. We examined variables affecting these parameters in coastal trees in British Columbia using data from 29 763 trees at 1412 sites in 170 watersheds. Tree diameter (diameter at breast height (DBH)) was the most important predictor of platform availability in the pooled data and within each of six regions. In most regions, platforms become available at DBH > 60 cm, but on East Vancouver Island, DBH needs to be >96 cm and possibly on the Central Coast >82 cm. Other regional predictors of platforms included tree height, tree species, and to a lesser extent elevation, slope, and latitude. Most (72%) trees providing platforms had epiphytes (mainly moss) covering one third or more of branch surfaces and 81% had intermediate or thick epiphyte mats. Mistletoe deformities provided <7% of platforms. Our model predictions help to define and manage suitable habitat for nesting Marbled Murrelets and also contribute to understanding forest canopy ecosystems. [ABSTRACT FROM AUTHOR]