Nesting 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 and commonly 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 determine if murrelets have habitat preferences within old growth forests It is important to look at selected nest sites compared to the available habitat All old growth redwood Douglas fir habitat has been assumed to constitute suitable nesting habitat but that may
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