Ralph and Long 



Chapter 35 



Productivity in California-Observations At Sea 



other areas were: Trinidad 18 July; Eureka 17 July; and 

 Santa Cruz 8 July. The last two juveniles that were identifiable 

 to age were observed on 8 September near Trinidad. 



The percent of the adult population in molt, including 

 both definite and probable categories, was fairly constant 

 from late June until mid- August (fig. 1). A bird was considered 

 to be in molt if there was a patch of basic plumage on its 

 breast, side, or belly. Even at the beginning of the study 

 period in late June, 25 percent of the 16 birds observed were 

 molting, though in the larger sample (n = 84) for the next 



period had only 10 percent molting. However, from 1 1 July 

 onward, we found no appreciable change in the proportion 

 of molting birds until 20-29 August, when a sharp increase 

 to 75 percent was recorded. By 9 September, 95 percent of 

 the birds were molting. 



There was also a marked increase of birds with the 

 appearance of basic plumage (while sitting on the water), 

 including both juveniles and molting adults, during the 9-18 

 September period (fig. 2). Along with the birds of unknown 

 age in basic plumage, we included those molting adults in 



235 



55 



Figure 1 Percent of known adults in molt by 10-day periods. Date indicates 

 the first day of each period. Total number of birds identified as adults (definite 

 and probable) for each period is indicated on the top of each bar. 



UNKNOWN 



23 19 





Si CM 





Figure 2 Percent of the total population with black-and-white plumage (both adults and 

 juveniles) by 10-day periods. Remaining birds are adults in alternate (breeding) plumage. 

 Columns show percent of black-and-white birds which were juveniles, adults, and of 

 unknown age. Definite and probable categories for juveniles and adults were combined. 

 Date indicates the first day of each period. Total number of murrelets observed for each 

 period is indicated on the top of each bar. 



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



375 



