O'Donoell and others 



Chapter 11 



Patterns of Seasonal Variation of Activity 



1989 



1990 



H 



U 



U 

 Q 



U 

 S 



Figure 11 Mean number of Marbted Murretet detections per week at Bloom's Creek Campground, 

 California, in 1989-1990 (upper) and 1990-1991 (tower). Each weekly mean was calculated from 1-3 

 intensive dawn inventories. Asterisks (*) indicate that a survey was conducted but no murrelets were 

 detected; all other blank columns represent weeks in which no data was collected. From Naslund 1 993b. 



generally at the southern end of each species' range (Ainley 

 and Boekelheide 1990, Greenwood 1987, Harris 1985, Harris 

 and Wanless 1989, Taylor and Reid 1981, Sydeman 1993, 

 Thoreson 1964). Harris and Wanless ( 1989) found a positive 

 correlation between winter visitation and breeding success 

 in the previous and following breeding season for a 

 population of marked Common Murres. Winter attendance 

 at breeding stands by murrelets may similarly relate to 

 prior reproductive success, and might also enhance pair 

 bond maintenance, facilitate earlier breeding (Carter and 

 Erickson 1988), and reinforce familiarity with flight paths 

 to the breeding stands. 



Two periods of very low (or no) activity occurred during 

 March and from mid-August through early October. The 

 pre-altemate molt period in California may begin as early as 

 mid-February and extend through March (Carter and Stein, 

 this volume). The relatively low level of March detections 

 levels probably reflects this molt. Although murrelets do 



not molt flight feathers at this time (Carter and Stein, this 

 volume), the increased energetic demands of molting body 

 feathers could limit inland visits. The second period, from 

 mid-August through early October coincides with the 

 cessation of nesting and the molt into basic plumage. The 

 more extensive nature of this prebasic molt (full body and 

 simultaneous wing molt of the adults) is reflected in the 

 longer period of time murrelets are absent from the forest. 



Numbers of above canopy behaviors closely mirror 

 the patterns of total detection levels through the year, with 

 the greatest levels occurring in the summer months and 

 lower levels during the remainder of the year. Detections 

 of birds below the canopy, however, coincide with the 

 breeding season (April through September), and are largely 

 absent outside of this period. Investigations of murrelet 

 behavior around nest sites have consistently reported on 

 observations of single birds and pairs flying below the 

 canopy in the vicinity of nest trees (Nelson and Hamer, this 



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



125 



