O'Donnell and others 



Chapter 1 1 



Patterns of Seasonal Variation of Activity 



3- 



ABOVE CANOPY 

 BELOW CANOPY 



APR MAY JUN JUL AU6 



MONTH 



(b) 



Figure 1 5 (a) Mean size of Marbled Murrelet flocks observed above and below the 

 canopy during the breeding season at James Irvine Trail, California, 1989-1991. 

 Surveys from all years were combined. The numbers of surveys in each month are 

 shown above the bars. An asterisk (*) denotes a significant difference (P = 0.05) 

 between above and below canopy flock sizes in the respective month; (b) Results of 

 Ryan-Einot-Gabriel-Welsh multiple range tests comparing above and below canopy 

 flock sizes between months. Months with the same letter indicate that the mean flock 

 sizes were not significantly different from each other. 



recommend that of four surveys conducted within a summer, 

 two be conducted after 20 June, and at least one be conducted 

 during the last three weeks of July. The earliest that birds 

 were no longer detected at a stand in northwestern California 

 was on 17 August (O'Donnell 1993). Detections of murrelets 

 below the canopy, however, are absent earlier than this, and 

 therefore 5 August is a reasonable termination date for the 

 murrelet survey season in California. 



Naslund (1993b) speculates that the population of birds 

 visiting breeding stands during the winter may consist of a 

 higher proportion of resident breeders than during the summer. 

 Therefore, she suggests that surveys conducted during the 



winter may actually monitor, for management purposes, the 

 most important segment of the population (i.e., breeding 

 birds). Until the relevance of winter numbers is established, 

 however, surveys should continue in the breeding season. 



Acknowledgments 



We thank Jim Baldwin, Ann Buell, Alan E. Burger, 

 Peter Connors, George Hunt, Debbie Kristan, S. Kim 

 Nelson, Lynn Roberts, Michael Rodway, Jean-Pierre Savard, 

 Fred Sharpe, and Sherri Miller for helpful comments on 

 this manuscript. 



128 



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



