Miller and Ralph 



Chapter 20 



Inland Habitat Relationships in California 



In most forests, the majority of detections are audio and 

 are not affected by canopy cover. Though the number of 

 visual detections decreases with increased canopy cover, 

 there should be a compensating effect as we have found 

 higher numbers of total detections (e.g., Paton and Ralph 

 1990) as forest age and canopy cover increase. 



In calculating P, the probability of at least one detection 

 in a stand, we assume that murrelets are present in the stand 

 when the survey is conducted. 



The effects of this assumption are discussed in detail 

 in Azuma and others (1990), and the situation with the 

 murrelet is similar. Since there is some probability that 

 murrelets will be present in a stand and not be detected, the 

 result would be an underestimate of the number of stands 

 with murrelets present. Following data collection, bias 

 adjustments presented in Azuma and others (1990) could 

 be used to estimate the number of stands with murrelets in 

 each stand category. 



We assume that P is constant and independent of stand 

 size and habitat type. 



It is possible that as stand size increases and habitat 

 matures, the number of birds in a stand will increase. 

 Increased numbers will likely increase P as individuals 

 may call in response to other birds as a result of social 

 facilitation. Therefore, stands with few birds will have 

 fewer detections than stands with many birds. We will be 

 examining this assumption, and it forms the basis of the 

 null hypothesis that stand size and habitat type have no 

 effect on detection rate. 



Frequency of surveys 



If the habitat is homogeneous and we assume that 

 the birds are distributed essentially evenly throughout the 

 stand, the stations can be positioned throughout the stand 

 and all stands, regardless of size, would be surveyed four 

 survey mornings. 



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



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