O'Donnell and others 



Chapter 11 



Patterns of Seasonal Variation of Activity 



WEEK BEGINNING 



Figure 7 Weekly mean numbers (bar segment) of Marbled Murrelet detec- 

 tions per survey per week along upper Carmanah Creek, British Columbia. 28 

 May to 27 August 1990. The standard error (line segment) and number of 

 surveys in each week are also given. From Manley and others 1992. 



and summer detection levels on Mitkof Island, Alaska (Doerr, 

 pers. comm.; Walsh, pers. comm.). 



The remaining two months, March and September, had 

 low to no activity (Naslund 1993b, O'Donnell 1993). In 

 northwestern California, detections in March ranged from 

 four to seven percent of those in July, and September levels 

 were less than one percent of July levels. Detection levels in 

 March and September were usually significantly lower than 

 all other months (O'Donnell 1993). 



Patterns of Absence from Stands 



Marbled Murrelets are most often absent, or in much 

 reduced numbers, from breeding stands during the two 

 transition periods: (1) March, and (2) mid- August through 

 October (Naslund 1993b, O'Donnell 1993) (figs. 10, 11). 

 Doerr and Walsh failed to detect murrelets from 27 August 

 to 2 October 1992, at their study site on Mitkof Island, 

 Alaska (Doerr, pers. comm.; Walsh, pers. comm.). In central 

 California, from 1989 through 1991, the proportion of surveys 

 in August through October with murrelets present was 

 significantly lower than for surveys in summer, in winter, or 

 in March (Naslund 1993a). Similarly, murrelets were observed 

 on a significantly smaller proportion of surveys in March 

 than during summer or winter (Naslund 1993a) (fig. 13). At 

 nine sites in northwestern California from 1989 through 

 1 99 1 , murrelets were not detected on 3 3 percent of 30 surveys 



conducted in March, nor on 3 1 percent of 80 surveys conducted 

 in August through October (O'Donnell 1993). In addition, 

 surveys with no detections occurred with significantly greater 

 frequency from November through February than from April 

 through July. Murrelets were not detected on 10 of 7 1 counts 

 conducted from November through February, while birds 

 were detected during all but one of 227 surveys from April 

 through July (O'Donnell 1993). 



Variation in Frequency of Behaviors and 

 Flock Sizes 



Flight Altitude 



The behavior classes recorded during murrelet surveys 

 differentiate between two classes of behaviors, those occurring 

 above the forest canopy, and those at the top, below, and 

 within the forest canopy. These latter behaviors occurring at 

 or below the canopy we will refer to as "below canopy 

 behaviors", and are considered most indicative of probable 

 nesting (Ralph and others 1993). They have also been referred 

 to as "occupied behaviors", that is, indicative of birds occupying 

 a given stand for nesting. Studies in California (Naslund 1993b, 

 O'Donnell 1993) found that the numbers of different behaviors, 

 both above and below the canopy, differed significantly between 

 months through the year (table 1). O'Donnell (1993) detected 

 murrelets flying above the canopy throughout the year at three 

 sites in northwestern California. The patterns of behaviors 



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



121 



