O'Donnell and others 



Chapter 11 



Patterns of Seasonal Variation of Activity 



250 



200 - 



100- 



5 50- 



HAY 



JUNE 



JULY 



AUGUST 



Figure 9 Numbers of detections of Marbled Murrelets throughout western Prince 

 William Sound, Alaska, during the 1992 breeding season. Data was collected at 67 

 randomly selected (boat-based) sites. From Kuletz and others 1994c. 



was greater during the winter, from October through 

 February, than from March through August at both sites. 

 For instance, at Lost Man Creek the mean numbers of calls 

 per detection ranged from 7.4 to 9.3 from October through 

 February. From March through August mean calls per 

 detection ranged from 3.7 to 6.1 at this site. Numbers of 

 calls were significantly different between months only at 

 Lost Man Creek. 



Rodway and others (1993b) compared levels of vocal- 

 izations between months at two sites in the Queen Charlotte 

 Islands, British Columbia. Months compared were May 

 through July at the Lagins Creek site, and May through 

 August at the Phantom Creek site. They examined changes in 

 both the number of calls per detection (all calls counted), as 

 well as number of calls per survey (detections with "multiple" 

 calls assigned a value of 25). Number of calls per detection 

 were similar in May, June, and July at both sites. At Phantom 

 Creek, vocalization levels dropped significantly after July 

 24. Number of calls per survey increased through July, reaching 

 peaks in the last week of July at both sites, and falling rapidly 

 in the second week of August at Phantom Creek. 



O'Donnell (1993) also looked at the occurrence of grunt 

 or groan calls (previously referred to as alternate calls) for 

 evidence of seasonal patterns (Paton, this colume; Nelson 

 and Hamer. this volume a). He compared between months, 

 for above and below canopy detections, the proportion of 

 detections which included these calls, and found seasonality 

 was not marked. Only at Lost Man Creek, where the sample 

 was greatest, was there significant differences between 

 months in the proportions of detections above the canopy 

 with alternate calls. These calls occurred in lower proportions 

 in December through February than in the remainder of the 

 year. However, a subsequent multiple range test did not 

 distinguish any significantly different months. The 

 percentage of detections of murrelets giving grunt calls 

 below the canopy also showed seasonality only at Lost 



Man Creek, where they occurred in significantly greater 

 proportions during July. 



Flock Size 



Changes in flock size through the breeding season have 

 been noted in two studies (O'Donnell 1993, Rodway and 

 others 1993b). O'Donnell (1993) found that both nocks 

 observed above and below the canopy were smallest during 

 May and June at each of three sites in California. Above 

 canopy flocks at the Experimental Forest site had significantly 

 fewer birds in June, and were also smaller in June at James 

 Irvine Trail, though not significantly so (fig. 15). At Lost 

 Man Creek, flocks above the canopy had significantly fewer 

 murrelets in May, and significantly more birds in July. 

 Reduction in the size of flocks below the canopy was especially 

 marked at James Irvine Trail, where flock size was 

 significantly less in May and June than during the remaining 

 summer months (fig. 15). Below canopy flocks with the 

 fewest numbers occurred in June at all three sites. 



Rodway and others (1993b) similarly detected smaller 

 flocks during May and June at their two sites in British 

 Columbia. Single birds were observed most frequently in 

 these two months, and flocks of two were most common in 

 July at both sites. 



Discussion 



Seasonal Patterns of Behavior and Activity 



Marbled Murrelets show consistent, seasonal patterns of 

 activity and behavior. Throughout their range they exhibit the 

 greatest levels of inland activity from April through August, 

 with peak levels usually occurring from about the second 

 week of July through early August. Hamer and Cummins 

 (1990) suggested greater detection rates in late July may reflect 

 increased food needs of nestling murrelets and the consequent 

 increase in foraging trips by parent birds. Paton and Ralph 



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



123 



