Hamer 



Chapter 17 



Inland Habitat Associations in Western Washington 



and others 1994). Single observers visited each stand three 

 or more times during the breeding season (1 May-5 August) 

 recording observations during a 2-hour dawn survey period 

 each visit. Mean detection rates for each stand were calculated 

 by dividing the total number of detections by the number of 

 survey visits. To standardize this calculation, stands with <3 

 visits were not used in the analysis. These stands would not 

 have had enough survey effort to determine occupancy with 

 sufficient likelihood. For sites with >4 visits, survey visits 

 were removed by selecting those four visits that best 

 represented the seasonal timing of surveys recommended by 

 the Pacific Seabird Group survey protocol. This helped 

 standardize the selection of surveys in order to equalize the 

 survey effort between stands. Therefore, survey effort was 

 standardized by using only three or four visits for each stand 

 used in the analysis. 



Occupied sites were defined as those stands with birds 

 observed flying through the canopy, in or out of the canopy, 

 birds observed landing or perched in trees, or stands with 

 murrelets observed circling over the canopy (Ralph and 

 others 1994). Occupied sites also included stands where nest 

 platforms, murrelet egg shells, or juveniles had been found. 

 Unoccupied sites included stands with birds present, but 

 where no occupied or below canopy behaviors were observed, 

 and stands where birds were not detected. 



Stand Characteristics 



Old-growth stands were included in the study if they 

 met the definition of old-growth developed by the Washington 

 Department of Wildlife Remote Sensing Program. Old-growth 

 stands were defined as having at least 20 dominant overstory 

 trees per hectare that were >8 1 cm diameter at breast height 

 (d.b.h.). Co-dominant trees were >40 cm d.b.h. The presence 

 of at least 2 canopy layers was also required. 



Vegetation Quantification 



A total of 38 attributes describing forest characteristics 

 were used in the analysis (table 1). Observers were trained 

 during a 3-day period to ensure forest variable measurements 

 and estimates were performed consistently by all crew 

 members. Vegetation data was not obtained from all the 

 stands that were surveyed, therefore the sample size for the 

 vegetation analysis was less than the number of stands used 

 in the comparisons of mean detection and occupancy rates. 

 Vegetation measurements were obtained from 64 occupied 

 and 87 unoccupied old-growth stands located throughout 

 western Washington for a total sample size of 151 stands. 



The sample size of stands where vegetation data was 

 collected was variable in each physiographic province (table 

 2). Old-growth stands in the North Cascades and Puget 

 Trough Physiographic Provinces were selected systematically 

 to represent a range of elevations, forest zones, and geographic 

 areas. One to several stands were selected from each drainage 

 depending on drainage size and access. Old-growth stands in 

 the Olympic, South Cascades, and Coast Range Physiographic 

 Provinces were selected in a opportunistic manner, primarily 



from a need to conduct surveys for Marbled Murrelets in 

 certain stands because of impending forest harvest plans or 

 other land management projects. The North Cascades and 

 Olympic Peninsula physiographic provinces contained the 

 largest proportion of sites because these provinces were 

 areas where research had been conducted earlier and more 

 intensively. 



Because murrelet detection rates were found to decline 

 with increasing inland distance, not all stands that were 

 surveyed were used in the statistical analysis. Some stands 

 may have possessed all the appropriate structural features 

 required to produce suitable nesting habitat, but were 

 unoccupied because the inland distance was too great. To 

 avoid misinterpreting study results, only stands <61 km 

 from salt water were used in the vegetation analysis. I arrived 

 at this value by examining the relationship between murrelet 

 abundance and the inland distance of stands. 



Sites <0.8 km from salt water were not used in any 

 analysis. Over the last three years a total of nine unoccupied 

 sites have been located in Washington <0.8 km from salt 

 water, with what appears to be excellent murrelet nesting 

 habitat. This included five sites from southwest Washington 

 and the Puget Trough, and four sites from the San Juan 

 Islands. Murrelets may avoid using these stands because of 

 their exposure to wind and coastal storms, or because of the 

 presence of a higher number of predators such as gulls 

 (Larus spp.), and crows and ravens (Corvus spp.). 



Survey stations were located in or adjacent to old-growth 

 stands with a minimum stand size of 50 ha. This is an area 

 encompassed by a circle with a 0.4 km radius and was 

 therefore the sampling unit used for the study. From field 

 experience I felt that this would be the approximate area an 

 observer could detect murrelets on the landscape, and also 

 prevented the surveying of small old-growth stands in heavily 

 fragmented areas. These smaller stands may have a lower 

 abundance of murrelets because they lack a sufficient amount 

 of habitat, rather than a deficiency in any particular structural 

 feature of the forest. Stand size was not included as a variable 

 in the study design. This was due to the large number of 

 observation stations per stand needed to successfully measure 

 this effect, and the large sample of stands required for the 

 statistical design. Although the influence of stand size on 

 murrelet abundance is a vital piece of information required 

 by land managers, more extensive research will be needed to 

 evaluate this variable. The mean stand size or age of the 

 stands sampled was not determined. 



The forest vegetation was measured using one 25-m 

 radius plot for each old-growth stand being surveyed. The 

 exact location of the plot was chosen by placing it in an area 

 where flight behaviors below the canopy indicated possible 

 nesting or, in other stands, in an area with the highest murrelet 

 activity. For stands with no activity, the plot was located in 

 an area with the highest stem density and largest basal area 

 of old-growth trees. Therefore, even in areas with no activity, 

 the highest quality old-growth available was selected to 

 represent the stand thus establishing a conservative analysis. 



164 



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



