Hamer 



Chapter 17 



Inland Habitat Associations in Western Washington 



and lichen coverage (mean lichen) on the limbs of dominant 

 trees. Sites with a high probability of occupancy had a 

 mean canopy closure of 86 percent. 



Importance of Independent Variables 



The step in which each variable was selected, the stability 

 of variables through the stepwise procedure, the final chi- 

 square values of variables used in the model, and the 

 relationship between variables were used to subjectively 

 assess the relative contribution of variables in predicting the 

 probability of occupancy (table 3). The variables most 

 correlated with occupancy of old-growth stands, included 

 total potential nest platforms/ha, total percent moss cover on 

 tree limbs, percent slope, mean d.b.h. of all dominant trees, 

 mean lichen cover on tree limbs, stem density of dominant 

 trees, elevation, canopy closure, mean d.b.h. of western 

 hemlock, and percent composition of low elevation conifers. 



Describing Low- and High-Quality Habitat 



To begin to define what values would be considered to 

 be the lower and upper thresholds for describing murrelet 

 nesting habitat, the minimum, mean, and average values for 

 each forest variable were calculated for occupied and 

 unoccupied stands (table 4). Suitable murrelet nesting habitat 

 was defined as sites with a high probability of occupancy. 

 These stands had a mean topographic slope of 50 percent 

 and were found at a mean elevation of 152 m. Stands with a 

 high probability of occupancy also had a mean of 92 platforms/ 

 ha, a stem density of 50 dominant trees/ha (>81 cm d.b.h.), 

 83 percent canopy closure, 101 cm mean d.b.h. of western 

 hemlock, 49 percent moss coverage on tree limbs, and a low 

 index of lichen cover (table 4). 



Stands with a high probability of occupancy (>0.76) had 

 minimum values of 10 platforms/ha, 29 dominant trees/ha, 

 29 percent canopy closure, 85 cm mean d.b.h. of western 

 hemlock, 5 percent moss cover, and 97 cm mean tree d.b.h.. 

 These occupied stands were found at a maximum of 288 m 

 in elevation. 



Tree Characteristics 



A comparison of old-growth tree characteristics for 

 different conifer species in Washington indicated that old- 

 growth Sitka spruce had most of the characteristics associated 

 with known nest sites (Hamer and Nelson, this volume b). 

 Sitka spruce had a higher mean d.b.h., taller height, higher 

 number of platforms/tree, and higher moss coverage of the 

 limbs than any of the five other conifers (table 5). On 

 average, this species had more than two times as many 

 platforms/tree than any other conifer species except Douglas- 

 fir. Douglas-fir was second in having characteristics deemed 

 suitable for murrelet use, with a similar number of platforms/ 

 tree as Sitka spruce, a large height, high mean d.b.h., but a 

 low moss coverage on the limbs. Western red cedar ranked 

 third as a suitable nest tree choice with a large mean d.b.h., 

 high basal area, 1 .4 platforms/tree, and one of the highest 

 moss cover indexes. Western hemlock ranked fourth in the 



comparison but, as expected, has one of the highest mistletoe 

 indexes of any tree species. Mountain hemlock ranked third 

 and silver fir last. Both silver fir and mountain hemlock had 

 a low mean d.b.h., low basal area, low number of platforms/ 

 tree, and a higher lichen index. Silver fir had an average of 

 only 0.81 platforms/tree. 



Discussion 



Landscape Characteristics 



Distance to Salt Water 



Because murrelets forage at sea and only carry single 

 prey items to the nest, but can nest at long distances from the 

 coast, the energetic requirements of flying inland to incubate 

 eggs and feed young, places a limit on their inland breeding 

 distribution and use of inland forests. Even with the potential 

 problems of energetic expenditure, Marbled Murrelets 

 displayed a great tolerance for using nesting stands located 

 up to 63 km inland from the ocean. Almost all the habitat in 

 the North Cascades and South Cascades Physiographic 

 Provinces is located >42 km inland because of rural 

 development and intensive forestry practices within the Puget 

 Trough. Even with these long flight distances, some birds 

 were passing occupied stands to fly farther inland. 



Breeding records also indicated that nesting is 

 occurring at stands located long distances from salt water. 

 A small downy chick was located on the ground along a 

 trail on the east shore of Baker Lake in 1991, 63 km from 

 the ocean (pers. obs.). Another downy chick was located 

 45 km inland at Helena Creek, in Snohomish County (Reed 

 1991). Six additional records of eggs, downy young, and 

 fledglings found 29-55 km inland in Washington were 

 compiled by Leschner and Cummins (1992a), and Carter 

 and Sealy( 1986). 



Elevation 



In general, stands found at higher elevations had a lower 

 composition of conifer species reported to be used as nest 

 trees. Murrelet nests have not been located in the higher 

 elevation conifers such as silver fir or mountain hemlock in 

 British Columbia, Washington, Oregon, or California, (Hamer 

 and Nelson, this volume b). A negative association of murrelet 

 abundance and stand occupancy to the occurrence of silver 

 fir and mountain hemlock (high elevation tree species) is 

 best explained by these species low mean d.b.h. and low 

 number of platforms/tree (see Tree Characteristics). In 

 addition, silver fir branches generally exit the trunk at sharp 

 downward angles creating few level platforms. 



Forest Type and Physiographic Province 



All records of nests, eggs, eggshell fragments, and downy 

 chicks in Washington have been associated with old-growth 

 forests (n = 17) (Leschner and Cummins 1992a). In North 

 America, fledglings have been found in a variety of unusual 

 habitat types such as roads, airports, and rural areas (Carter 

 and Sealy 1987b; Hamer and Nelson, this volume a). These 



170 



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



