Ralph and others 



Chapter 1 



Overview of Ecology and Conservation 



either as a function of the distance from the coast, or the 

 thickness of growth limiting the ability of birds to fly into the 

 stand, is also likely a factor involved in nest site selection. 



Stand size has been suggested to be an important factor 

 in the abundance of birds in a stand (Paton and Ralph 1990) 

 and in the likelihood that a stand will be occupied (Raphael 

 and others, this volume). Larger stands can contain more 

 birds overall, but there is no evidence that density changes 

 as a function of stand size (Miller and Ralph, this volume). 

 Stand size, however, is probably importantly related to some 

 of the other factors mentioned above, especially predation. 



Potential Biases in Determining Nest Sites 



Observers have usually chosen sites for nest search in 

 areas with larger trees. Data from stratified samples for 

 presence of birds in inland stands in California (Miller and 

 Ralph, this volume), in Oregon (Nelson 1990), and in Alaska 

 (Kuletz and others, this volume), as well as nests discovered 

 from radio-tracking (Hamer and Nelson, this volume b), 

 have probably been the most free of bias. Since these more 

 randomly located sites have not differed markedly from the 

 nest sites found in search areas that were potentially biased 

 by the choice of area to be searched, we conclude that the 

 documented nest sites described in most studies are 

 representative of habitat selection by the species. 



Sources of Error in the Determination of Forest Use 



The most direct evidence of murrelet breeding is the 

 finding of a nest, but nest detections are rare, due to the 

 secretive nesting behavior of murrelets. Also, as Hamer and 

 Nelson (this volume b) point out, locating nests is greatly 

 dependent upon where observers have looked, making the 

 habitat characteristics of nest sites subject to this bias. The 

 majority of the conclusions about murrelet use of habitats 

 relies upon detections of birds that have flown inland to 

 presumed nesting areas (Naslund and O'Donnell, this volume; 

 O'Donnell and others, this volume; Paton, this volume). 

 Observations have been divided into two groups, those of 

 birds flying over the canopy and those at or below the 

 canopy level (Ralph and others 1993). It is suggested that the 

 latter behavior (referred to as "occupied" behavior) is a 

 strong indication that breeding is occurring in the stand, as 

 this behavior is almost entirely restricted to the breeding 

 season (O'Donnell, this volume). 



We believe that the most objective method of 

 determining habitat relationships is the detection of birds in 

 the forest. Detections are usually within a 100-m-radius 

 circle surrounding the observer, and provide a larger and 

 less potentially biased sample than the location of nest 

 trees. Below-canopy behavior has been observed in the 

 vicinity of known nest trees. Despite the lack of data 

 demonstrating that this behavior occurs only when a pair is 

 nesting or prospecting, we suggest that the presence of this 

 behavior is a strong indication that murrelets are nesting or 

 intending to nest in a given stand. Stands where murrelets 

 exhibit this behavior should be treated as if they contain 



nesting murrelets. Circling above the canopy is also thought 

 to be associated with nesting murrelets (e.g., Nelson and 

 Hamer, this volume; Nelson and Peck, in press). Other 

 species of alcids often circle above the breeding grounds as 

 part of their social interactions. However, as Divoky and 

 Horton (this volume) argue, the possibility that non-breeding, 

 dispersing young could be prospecting in marginal stands, 

 thus distorting the value of these stands to the observers, 

 cannot be dismissed. 



Seasonality of the murrelets' visits may affect efforts to 

 establish use of a stand. O'Donnell and others (this volume) 

 describe the seasonal timing of forest visits, showing the 

 peak of activity to be during the period of April through 

 July, with peaks of activity in the more northern parts of the 

 range occurring later in the summer. Naslund (1993) suggested 

 that the winter visits of murrelets to stands, even though 

 little or no below-canopy behavior is observed, might be a 

 better indicator of nesting than those during the breeding 

 season. However, we feel that until more compelling evidence 

 is available, stand use during the breeding season should 

 remain the criterion of breeding for management purposes, 

 as suggested by Ralph and others (1993). 



Many land managers depend upon the protocol developed 

 by the Pacific Seabird Group (Paton and others 1990; Ralph 

 and others 1993) to determine if murrelets are present in 

 their forests. The basis of the timing and frequency of the 

 surveys has depended upon a firm foundation of research as 

 summarized in O'Donnell and others (this volume), Naslund 

 and O'Donnell (this volume), and O'Donnell (this volume). 

 Active research and statistical analyses are underway to 

 validate the method and to determine the number of surveys 

 necessary to establish birds as breeding in a stand, and how 

 many years of survey are necessary. At issue is the possibility 

 of interannual variation in occupancy of a site that requires 

 protection. Ralph (this volume) found no significant 

 differences among years in detection levels at three sites in 

 California during years when there was a range of sea 

 temperature conditions, with both El Nino (the periodic 

 warming of ocean waters) and non-El Nino years during the 

 study. However, Nelson (pers. comm.) suggests that her data 

 show consistent differences among these same years in 

 Oregon. Burger (this volume a) also found higher inland 

 detection rates with normal sea temperatures, and lower 

 detections with high sea temperatures. Additional work needs 

 to be done to determine if differences in offshore conditions, 

 resulting in changes in food abundance and perhaps breeding 

 frequency, are reflected in inshore detections during the 

 breeding season. 



Local Distribution at Sea and Foraging 



Concentrations 



Patterns in the distribution of Marbled Murrelets at sea 

 can be seen both at large scales (hundreds of kilometers) and 

 at small scales of individual aggregations. The small-scale 

 distribution of Marbled Murrelets at sea reflects their choice 

 of foraging habitat. 



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



