Nesting Habitat Characteristics of the Marbled Murrelet in Central California Redwood Forests

The marbled murrelet (Brachyramphus marmoratus) is a threatened seabird that nests in old-growth forests in the Pacific Northwest. Despite concern for this species, little has been published on murrelet nesting habitat in the coast redwood (Sequoia sempervirens) region. Here we present the first comprehensive study of marbled murrelet nesting characteristics in redwood forests based on confirmed nest sites. In this study, we 1) described habitat characteristics at 17 murrelet nest sites in the Santa Cruz Mountains, California, USA, located using radiotelemetry and visual searches, and 2) compared nest sites with random sites located in nearby stands and centered on trees >= 120 cm diameter at breast height (dbh [potential nest trees or PNTs]). All 17 nests were located in stands of old-growth redwood forest and the mean dbh of nest trees was 210 cm (SD =91 cm). Eighty-two percent of nests (90% of telemetry-found nests) were in unharvested stands and 18%, all on private property, had been lightly harvested but did not contain significantly fewer trees >= 120 cm dbh than unharvested nest sites. Twelve of 15 (80%.) nests for which we were able to locate the nesting platform were on limbs and the remaining 3 (20%), all in redwood trees, were located on broken tops. Nest trees were significantly larger than PNTs and tended to be Douglas-fir (Pseudotsuga menziesi) despite the fact that nest stands were dominated by redwoods, perhaps because of greater nest platform availability in Douglas-fir trees. Nest sites were located closer to streams, had a greater basal area of trees >= 120 cm dbh, and were located lower on slopes than random sites based on analysis of variance models. We classified 71% of nest sites correctly with a simple logistic regression model that included only nest tree dbh and distance to stream-a model that could be used by managers in the region to identify potentially suitable nesting habitat. Our findings indicated that murrelets in central California, USA, primarily use old-growth redwood stands for nesting but will use partially harvested stands if a significant residual component remains; stands that have experienced some harvest but retain old-growth characteristics should be considered potential murrelet habitat in redwood forests.