Status of the Marbled Murrelet in the Inner North Coast Ranges of California

Abstract

We sought to determine the presence or absence of marbled murrelets (Brachy- ramphus marmoratus) within the northern Inner North Coast Ranges of northwestern California. We conducted murrelet surveys and collected environmental data during 1995 and 1996 on na- tional forest lands that were south of the Klamath Mountains Section and within B. marmoratus management Zone 2 as designated by the Forest Ecosystem Management Assessment Team. Using a stratified random sampling design, we surveyed for murrelets within the 2 coniferous forest habitat types most likely to be used by murrelets: late mature and old-growth Douglas- fir (Pseudotsuga menziesii) and late mature and old-growth tanoak (Lithocarpus densiflora). We used the generalized binomial model to determine sample sizes and to estimate the power of survey results for a range of assumed levels of murrelet occurrence (p) and probabilities of de- tection (p'). In 1995 and 1996, we conducted 1424 surveys at 178 Douglas-fir sampling units, surveying 30.8% of the total amount of this stratum within the study area. In 1995, we con- ducted 760 surveys at 95 tanoak sampling units, surveying 58.6% of this stratum. We did not detect B. marmoratus in either habitat type. When we assumed a p of 0.03, and a p' of 0.10, the power of our surveys to detect murrelets was 0.95 and 0.81 for the Douglas-fir and tanoak hab- itat types, respectively. Given the high power associated with our results and the large pro- portion of the total potential habitat surveyed, we concluded that our study area was not within the current range of B. marmoratus. Most habitat characteristics, including corvid abundance, were similar to murrelet nesting habitat in other areas. The relatively high elevation and far- inland location, and the related characteristics of climate and habitat structure, may explain the apparent absence of B. marmoratus from our study area. Accordingly, we recommend that the Forest Ecosystem Management Assessment Team zone lines be adjusted so that the Inner North Coast Ranges are excluded from Zone 2.