ReferencesNesting Habitat and Selection of the Marbled Murrelet in Central California Lauren Baker Abstract Old-growth forests have been widely destroyed and fragmented in the Pacific Northwest over the last several hundred years. As a result, species dependent on old-growth forest are at a greater risk for decline. One such species is the marbled murrelet (Brachyramphus marmoratus), which nests in coastal, old-growth forests. The population of the species in the southern part of the range has been in decline due to the destruction of the birds’ nesting habitat, and in 1992 the murrelet was federally listed as threatened in Washington, Oregon and California (Ralph et al., 1995). Unfortunately, there have been relatively few studies on actual nest sites, because murrelets are extremely elusive nesters. In this project I aimed to better characterize nest trees, nest limbs and vegetation immediately surrounding nest trees of nests in Central California. I looked at 17 nests found in the area since the late 1980s, 10 of which were found in the last several years using radio-telemetry of tagged birds to track nesting birds. I followed the Pacific Seabird Group (PSG) protocol to collect information on the nest tree and vegetation in the surrounding 25-meter radius area. I also aimed to find out if murrelets were selecting for certain features when choosing nest sites over available sites. I did this by collecting data using the PSG protocol for random sites that were within a 1-kilometer radius area of nest sites. I performed paired t-tests on nest and random sites to looked for differences in the two. Results show that nest sites have higher total and midstory canopy cover, are closer to streams, are lower on the slope and that nest sites tend to have larger basal area per hectare of very large trees (>120 cm diameter at breast height (DBH)) including significantly higher basal area/ha of Redwood trees with >120 cm DBH. The results of this study will allow for better understanding of and management of marbled murrelet nesting habitat.Introduction The Marbled Murrelet (Brachyramphus marmoratus) is a seabird in the family Alcidae that forages at-sea but and breeds in coastal, old-growth forests in western North America. The murrelet ranges from the Bering Sea to central California, with approximately 200,000 individuals in Alaska, 50,000 in British Columbia, 5,500 in Washington, 5,000-15,000 in Oregon and 6,450 in California (Ralph et al., 1995). A large gap in the murrelet’s distribution occurs in California, where the northernmost population in Humboldt County is separated by 450 km from the southernmost population in central California (Nelson, 1997), presumably due to the harvesting of old-growth nesting habitat in Marin, Sonoma, and Mendocino Counties. The central California population has been in decline due to the wide-spread destruction of old-growth forests, increases in nest predator populations, and oil spills (Gaston and Jones, 1998; Nelson, 1997; Carter and Erickson, 1992). In 1992, the murrelet was federally listed as a Threatened species in Washington, Oregon and California (Ralph et al., 1995). Murrelet population size is closely related to the amount of unfragmented old-growth forest available (Meyer and Miller, 2002, Raphael et al., 2002). Because of the importance of nesting habitat to murrelet populations at the landscape scale, defining and quantifying habitat at the stand scale is a critical component of management planning. Previous studies of habitat at this scale have been attempted by comparing vegetation characteristics at occupied and unoccupied stands, where occupied stands are those where a murrelet was observed flying below the canopy (Paton et al., 1990). Typically, occupied sites have a higher percentage of old-growth cover and greater densities of dominant trees than random sites (Hamer, 1995; Grenier and Nelson, 1995; Miller and Ralph 1995). Studies based on actual nesting sites are lacking because nests have been very difficult to locate due to the birds’ secretive behavior (Hamer and Nelson, 1995). Nelson and Hamer (1995) summarized the habitat at 61 murrelet nests in Alaska, British Columbia, Washington, Oregon and California. All nest sites located in California were found in old-growth forests. Nest stands were dominated by coast redwood and Douglas-fir; stands had a mean distance of 13 ± 8 km inland, were located on the lower two-thirds of the slope, were 108 ± 67 meters to the closest stream, had 39 ± 6 percent canopy closure and had multi-layered canopies. Nest trees in California had an average diameter at breast height (DBH) of 278 ± 136 cm, an average height of 73 ± 8 meters, limb diameters of 35 ± 13 cm with 90 ± 28 percent cover above the nest andcommonly had declining or broken tops. The sample size for central California was small (n=5), however, precluding comparisons with available habitat. In the last several years, the use of radio-telemetry to follow the movements of individual birds has greatly increased researchers’ ability to locate murrelet nests (Bradley et al., 2002; Newman et al., 1999, Peery et al. in review). The objective of this project is to better characterize Marbled Murrelet nesting habitat in central California by including the five aforementioned nest sites and twelve new sites (total nest sites = 17) that have been found since Nelson and Hamer’s study. I will follow the Pacific Seabird Group Protocol for measuring Marbled Murrelet nest sites (Ralph et al., 1992, 1994), which involves standardized measurements of the nest tree, nest limb and nest stand scales. A second objective is to compare Marbled Murrelet nesting habitat use versus availability, where murrelets are considered to “select” habitat characteristics they use more than are available to them at random (Johnson 1980). Nesting sites will constitute “used” habitat and sites randomly distributed in old-growth forest in the Santa Cruz Mountains will constitute “available habitat”. By placing all random sites in old-growth stands, I am asking the question – what habitat characteristics within old-growth forests do Marbled Murrelets select for when nesting? Based on previous analyses of Marbled Murrelet nesting habitat associations (Meyer and Miller, 2002, Raphael et al., 2002), I assume that murrelets prefer old-growth forests over second-growth and heavily harvested stands and seek to
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