Burger 



Chapter 16 



Inland Habitat Associations in British Columbia 



differed from the previous studies, showing a smaller 

 proportion of sites at each extreme (fig. 6d). These results 

 emphasize that the single-year Queen Charlotte Islands and 

 Vancouver Island surveys provide only rough guides to the 

 expected patterns in a specific area. 



The effect of year-to-year variability in detection 

 frequency can be clearly seen when the Carmanah-Walbran- 

 Nitinat data are split into two periods (fig. 6b). The first 

 (1990-1991) was a period of normal sea temperatures and 

 high murrelet detections in the Carmanah-Walbran-Nitinat 

 forests, whereas the second (1992-1993) covered two years 

 with unusually high inshore sea temperatures and low murrelet 

 activity in parts of the forest (Burger 1994). The resultant 

 threshold patterns are quite different, showing that variable 

 factors affecting murrelets (such as El Nino effects) must be 

 considered when habitats are assessed on the basis of detection 

 frequency. If, for example, forest managers set a threshold 

 of 30 detections per survey to delineate optimal habitat, then 

 this would cover 50 percent of all sites sampled in the good 

 years (1990-1991), but only 7 percent of the same sites in 

 poor years (1992- 1993). 



In order to avoid such problems, managers would need 

 to be very conservative and use relatively low thresholds 



(e.g., means of 10 or 20 detections per survey) to delineate 

 high-quality habitat requiring preservation. Comparisons 

 among sites of the mean detection frequencies provides only 

 a crude estimation of the quality of a stand, particularly if 

 only one or two intensive surveys are made in a single 

 season. A more meaningful analysis would use the relative 

 frequency of occupied behaviors recorded over at least two 

 years (Ralph and others 1994), and surveys in British 

 Columbia should be directed towards this goal. 



Acknowledgments 



Preparation of this chapter was funded by the British 

 Columbia Ministries of Forests (Research Branch) and 

 Environment, Lands, and Parks (Wildlife Branch); I thank 

 Brian Nyberg and Don Eastman for their support. I thank 

 Rick Burns, Andy Derocher, Andrea Lawrence, Moira Lemon, 

 David Manuwal, Ken Morgan, Lynne Prestash, Martin Raphael 

 for valuable comments. Unpublished material was provided 

 by Andrew Bryant, Rick Burns, Paul Jones (Friends of Caren), 

 Moira Lemon (Canadian Wildlife Service), Irene Manley, 

 Misty MacDuffee (Western Canada Wilderness Committee), 

 and Lynne Prestash. 



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



161 



