Ralph 



Chapter 13 



Interannual Differences in Detections 



temperatures during an El Nino event may cause a reduction 

 in murrelet breeding effort, and thus influence inland 

 detection levels. The current El Nino has become the 

 longest on record, beginning in early 1991, or perhaps 

 even earlier. 



All of the sites studied had relatively high murrelet 

 activity, as compared to many sites elsewhere in the Pacific 

 Northwest. This may have had an effect of moderating 

 differences if social facilitation is a factor in levels of 

 murrelet activity. However, we have no data at present to 

 support such a supposition, although Shaughnessy (pers. 

 comm.) and Nelson (pers. comm.) found differences 

 between years when comparing murrelet use at a site. 

 Also, there is some evidence that detections vary as a 

 function of weather (Naslund and O'Donnell, this volume). 

 For example, there are frequently more detections on foggy 

 mornings. Thus, a year in which low detection rates would 

 have been expected might instead have normal detection 

 rates because of unusually foggy weather in that year. 

 However, the amount of daily variation induced by clouds 

 in our studies has been less than 20 percent (O'Donnell, 

 pers. comm.). 



The great variation between mornings at most sites 

 might be the key to the lack of significant difference among 

 years. However, the fact that the monthly average values 

 were quite similar indicates that no differences exist. 



I was unable to find any evidence that would suggest 

 that the number of detections of birds was consistently 

 lower or higher in any one of the five years. Therefore, 

 results of inland surveys used to determine presence or 

 absence of Marbled Murrelets in proposed timber harvest 

 stands would likely have been valid in any of these years in 

 this area of California. Caution must be used in applying 

 these data to other sites and regions, however, as only three 

 sites were surveyed, and the variance was large. 



I suggest that we need continued monitoring of murrelets 

 at established sites over several years, combined with careful 

 quantification of the many influences on inland detection 

 levels, to fully resolve the indications derived from this 

 study. This effort would greatly increase our understanding 

 of this bird and its use of inland habitats. 



Acknowledgments 



I am very grateful to the biologists who have worked in 

 the early dawn over the years to put together this data set. 

 Especially noteworthy are Sherri Miller, Brian O'Donnell, 

 and Linda Long. I thank Robin Wachs for her excellent help 

 in tabulating and analyzing these data. I also thank Jim 

 Baldwin, Ann Buell, George Hunt, Debbie Kristan, Kim 

 Nelson, Peter Paton, and Meg Shaughnessy for helpful 

 comments on the manuscript. 



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



137 



