Hamer and Nelson 



Chapter6 



Characteristics of Nest Trees and Nesting Stands 



Nest platforms in the Pacific Northwest had a mean 

 length of 32 cm and a mean width of 22 cm. The mean total 

 platform area was 842 square cm (table 3). In the Pacific 

 Northwest, moss (hothecium) formed the major proportion 

 of the substrate for 67 percent of the nests. Litter, such as 

 bark pieces, conifer needles, small twigs, and duff, was 

 substrate in 33 percent of the nests. For nests found throughout 

 North America, moss formed 49 percent of the substrate, 

 moss mixed with lichen or litter formed 30 percent of the 

 nests, and litter 21 percent (n = 37). All nests found in 

 Alaska had moss as a component of the nest substrate. 



Mean moss depth at, or directly adjacent to, the nest cup 

 was 4.5 cm (table 3). Mean litter depth was 5 cm for nests in 

 the Pacific Northwest. Mean moss depths in Alaska were 3.9 

 cm. The majority (86 percent) of nests in North America (n 

 = 52) had substrates that were >2 cm in depth with a large 

 number of nests (n = 16) having substrate depths between 

 3.1 and 4.0 cm (fig. 8). 



Nest platforms in the Pacific Northwest (n = 44) were 

 created by large primary branches jj 32 percent of the cases. 

 In addition. 23 percent of the rests were located on tree 

 limbs where they became larger in diameter when a main 

 limb forked into two secondary limbs, or a secondary limb 

 branched off a main limb. In many instances, branches were 

 also larger in diameter where they were attached to the tree 

 bole. Locations where a limb formed a wider area where it 

 grew from the trunk of a tree formed 1 8 percent of the nest 

 platforms. Cases of dwarf mistletoe infected limbs (witches' 

 broom) (9 percent), large secondary limbs (7 percent), natural 

 depressions on a large limb (7 percent), limb damage (2 

 percent), and an old stick nest (2 percent) were also recorded 

 as forming platforms. Multiple overlapping branches at the 



point where they exited the trunk of a tree were sometimes 

 used as a nest platform. Many of the tree limbs creating nest 

 platforms had grooves or deformations forming natural 

 depressions on the surfaces of the limb. 



Cover directly above the nest was high in almost all 

 cases in the Pacific Northwest, with a mean of 85 percent. 

 Eighty-seven percent of all nests had >74 percent overhead 

 cover. Cover above the nest platforms in Alaska was similar 

 to that in the Pacific Northwest (table 3). 



Discussion 



Marbled Murrelets have a limit on their inland breeding 

 distribution because of the energetic requirements of flying 

 inland to incubate eggs and feed young. They forage at sea, 

 carrying single prey items to the nest and feed their young 

 several times per day during the late stages of nesting. To 

 some extent, the inland distance information presented here 

 is biased towards lower values, because nest search and 

 survey efforts have been more intensive closer to the coast 

 in all regions, where higher murrelet detection rates make 

 locating nests an easier task. Even with the potential problems 

 of energetic expenditure, murrelets displayed a great tolerance 

 for using nesting stands located long distances from the 

 ocean. Evidence of breeding was common in California, 

 Oregon, and Washington, in areas located 30-60 km inland. 

 Unlike many other alcids, the Marbled Murrelet forages in 

 near-coastal shallow water environments. The use of tree 

 limbs as a nesting substrate may have developed because 

 older-aged forests were the only habitats that were abundant 

 and commonly available close to the foraging grounds of 

 this seabird. Areas of brush-free open ground or rocky talus 



2 3 4 5 6 7 8 9 10 >10 

 MOSS AND DUFF DEPTH AT NEST CUP (cm) 



Figure 8 The depth of moss and litter under or directly adjacent to the nest cup 

 for 52 nests of the Marbled Murrelet in North America. 



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



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