Strong and others 



Chapter 32 



Distribution and Population Estimates in Oregon 





Results and Discussion 



Distribution and Behavior 



Distribution Along Oregon 's Coastline 



Marbled Murrelets were distributed irregularly along 

 the length of the state, with peak number occurring in the 

 central region for all survey methods and years of surveys 

 (fig. 3 and 4). In 1993 it appeared as if the population was 

 distributed somewhat farther north (fig. 3). The area from 

 Cascade Head to Florence almost always held high numbers 

 of birds. High densities were recorded between Florence and 

 Coos Bay on the one survey of that area in 1992, but this was 

 not seen again on repeated surveys in 1993. Because of the 

 continuing ambiguity of results for this area, it was treated 

 as a separate region in population estimates. In both years 

 there was evidence of a shift to the north late in the season, 

 though it was slight in 1993. 



Distribution in Relation to Shore 



Distribution in relation to distance from shore was 

 dramatically different in the two years (fig. 5). Marbled 

 Murrelets were very concentrated within 1 km of shore for 

 much of the 1992 season, and broadly scattered within 5 

 km of shore in 1993. In most cases this resulted in lower 

 densities on coastline transects in 1993 (table 3). In 1992 

 there was a late-season shift to farther offshore which 

 coincided with the shift farther north described earlier (fig. 

 6 and Strong and others 1993). Offshore distribution was 

 more variable in 1993 but no seasonal shift away from 

 shore was apparent. 



Behavior 



In contrast to distribution offshore, recorded behaviors 

 of murrelets were essentially the same in the two years (fig. 

 7). Although we did not see any murrelet groups as large as 



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Figure 3 Average numbers of Marbled Murrelets from 1 00 m boat transect strips in 1 km segments off the Oregon coast. Numbers 

 on xaxis represent the number of times each segment was surveyed. Arrows indicate divisions between north, center, and south regions. 



344 



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



