Varoujean and Williams 



Chapter 31 



Abundance and Distribution in Oregon and Washington 



Table S Distribution of Marbled Murrelets on the outer coast of Washington based on aerial survey results, 4-5 September 

 1993. From north to south the study area is divided into two sections, with the southern section, from Tillamook Head to 

 Cape Elizabeth, located off sandy shores, and the northern section, from Cape Elizabeth to Cape Flattery located off 

 predominately rocky shores. Within each section the study area is delineated by distance from shore into an inner (<2,000 

 m) and outer (2,000-4,000 m) half 



* Location is represented as the extent of coastline between latitudinal listings 



+ AD = Adults in alternate plumage; BW = Black/White plumage, which includes adults in basic plumage and hatch-year birds. 



plumage or birds in black-and-white plumage, was similar, 

 indicating no preferred use of a particular section of coast 

 in either Oregon or Washington by any one group size or 

 plumage category. 



Production 



The ratio of hatch-year birds to the total number of 

 murrelets seen during the surveys is a potential estimator of 

 production. Of the 882 murrelets seen in Oregon, 203 birds 

 were recorded as being in black-and-white plumage, i.e., 

 adults in basic plumage and hatch-year birds. To obtain an 

 estimate of production requires ascertaining the number of 

 hatch-year birds in the black-and-white plumage category. 

 This was done by using figures obtained by Ralph and Long 

 (this volume) from northern California on the proportion of 

 hatch year birds to the total number of black-and-white birds 

 identified to age. During the period 20-30 August they 

 documented that 21 percent of the black-and-white birds 

 identified to age were hatch years. Therefore, if you assume 

 21 percent of the 203 black-and-white birds seen during the 

 aerial surveys (43 birds) are hatch years, the proportion of 

 hatch-year birds to the total of 882 murrelets seen in Oregon 

 is 4.9 percent. 



As there is about a one week delay in the onset of 

 murrelet nesting in Washington as compared to northern 

 California (Hamer and Nelson, this volume a), it is more 

 appropriate, even with the Washington survey occurring in 

 early September, to again use the hatch-year ratio for the 

 period 20-30 August, rather than the ratio of 11 percent 

 documented by Ralph and Long (this volume) for the period 

 30 August-9 September. Twenty-one percent of the 70 black- 

 and-white birds seen during the aerial surveys is 15 birds, so 

 the proportion of hatch-years to the total of 280 murrelets 

 seen in Washington and British Columbia is 5.4 percent. 



Discussion 



Abundance 



In general, the population estimate of 6,400-6,800 birds 

 corresponds to estimates previously reported for Oregon. 

 Several spatially limited surveys were conducted in Oregon 

 prior to 1992 (Nelson and others 1992), including boat- 

 based surveys carried out during the summers of 1986-1988 

 by Varoujean and Williams (1987) and Varoujean and others 

 (1989). These surveys, conducted while searching for 

 murrelets to capture for radio tagging, established a mean 

 density estimate of 23.2 birds/km 2 (n = 63, s.e. = 3.7). It was 

 felt, however, that murrelet density was overestimated, in 

 part, because the surveys were conducted off only central 

 Oregon, where murrelets are more abundant. Furthermore, 

 because murrelets were found to be episodically concen- 

 trating near the tidal plumes of river mouths and harbor 

 entrances, density estimates derived from transects carried 

 out solely within 3 km of these areas were significantly 

 higher (f-test, P<0.01), and more variable than on transects 

 that extended to and beyond 3 km from these entrances 

 (out to 3 km: x =54.1 birds/km 2 , n = 14, s.e. = 13.7, range = 

 6.7-190.0; out to/beyond 3 km: x = 13.5 birds/km 2 , n = 49, 

 s.e. = 1.6, range = 3.5-32.0). Varoujean and Williams (1987) 

 also noted variability in abundance in the same location 

 offshore of sandy beaches over periods of 2-4 days, which 

 they attributed to daily changes in the location and extent of 

 rip-current plumes. Murrelets were observed aligning 

 themselves on or near the boundaries of these plumes, 

 presumably for the purpose of foraging. The presence, 

 persistence, size and shape of these plumes depends on 

 shoreline morphology, tidal state, tidal range, and the 

 magnitude and direction of wind driven waves and long 

 ocean swells (Brown and McLachlan, 1990). With tidal ebb 



334 



USDA Forest Service Gen. Tech. Rep. PSW-152. 1995. 



