Burger 



Chapter 16 



Inland Habitat Associations in British Columbia 



diameter and total basal area of trees ranged from 46 to 

 123 cm, and 5.9 to 25.3 m 2 per 0.9 ha plot, respectively. 

 Frequencies of occupied detections were positively 

 correlated with both mean tree diameter (r = 0.729, n = 15, 

 P < 0.01) and basal area (r = 0.585, n = 15, P < 0.05), but 

 frequencies of all detections showed no significant 

 correlations (Manley and others 1994). These data suggest 

 that the murrelets were more sensitive to tree size than to 

 tree species composition in these old-growth forests. 



There have been no analyses of the effects of stand 

 size, edge effects or stand isolation on Marbled Murrelets in 

 British Columbia. 



Effects of Epiphytic Mosses and Mistletoe 



All nine nests known for British Columbia were on 

 platforms of epiphytic mosses. Dense mosses were associated 

 with the large trees in those vegetation groups in which 

 detection frequencies were highest in the Queen Charlotte 

 Islands (Rodway 1993a). In Carmanah-Walbran watersheds, 

 Burger (1994) found no correlation between murrelet detection 

 frequency and estimated moss cover per site, but the trees in 

 all of the sample plots were well endowed with mosses and 

 this was not a limiting factor for the murrelets here. 



None of the nine nests found in British Columbia were 

 associated with mistletoe. Murrelet detection frequencies 

 were not correlated with mistletoe index (Hawksworth 1977) 

 in Carmanah-Walbran in 1991 (11 sites) or 1992 (12 sites), 

 and moss-covered boughs provided many more potential 

 nest sites than mistletoe in these large trees (Burger 1994). 



Predator Abundance 



I found no records of predation of Marbled Murrelets 

 from British Columbia, but did not review all the raptor 

 literature. Marbled Murrelets were absent from prey remains 

 of Bald Eagles (Haliaeetus leucocephalus) found beneath 

 35 nests (which included 145 bird carcasses) in the Gulf 

 Islands (Vermeer and others 1989a) and 17 nests (33 bird 

 carcasses) in Barkley Sound (Vermeer and Morgan 1989). 

 Jones (1992) reported that murrelets fell silent and 

 disappeared for 10 minutes when a large owl (probably 

 Barred Owl [Strix varia]) appeared. 



Bryant (1994) tested the effects of egg predators in 

 montane western hemlock-mountain hemlock forest in 

 central Vancouver Island, using 120 artificial nests, each 

 with three quail eggs, placed on the ground or in trees at 

 eye level. He found that 43 percent of nests (52 percent of 

 eggs) were damaged or removed in the first week, and 87 

 percent (91 percent eggs) after two weeks. The survival of 

 both nests and eggs placed in trees was significantly higher 

 with increasing distance from the forest edge, after both 7 

 and 14 days (fig. 5). Nests of Marbled Murrelets are much 

 higher in trees and better camouflaged than these 

 experimental nests, and so would not necessarily experience 

 the same levels of predation. Nevertheless, these results 

 indicate a strong edge effect of nest predation, suggesting 

 that fragmentation of forests exposes Marbled Murrelet 



nests to increased predation. Steller's Jays (Cyanocitta 

 stelleri), Gray Jays (Perisoreus canadensis) and Common 

 Ravens (Corvus corax) were likely predators of tree nests 

 in this experiment. These corvids did not appear in Bryant's 

 census transects often enough to determine their distribution 

 (Bryant, pers. comm.). 



These results are consistent with the conclusions reached 

 by Paton (1994). In a critical review of 14 studies, he found 

 strong evidence that avian nest success was reduced by 

 predation and parasitism near habitat edges. Increased 

 predation of natural and artificial (experimental) nests was 

 most marked within 50 m of forest edges. In addition, nest 

 success was consistently correlated with habitat patch size. 

 There were apparently no studies in old-growth forest in the 

 Pacific Northwest, nor did any studies consider nests as 

 high in trees as those of the Marbled Murrelet. Studies on 

 the effects of edges and habitat fragmentation on nest success 

 of Marbled Murrelets are clearly a priority in areas with 

 intensive logging. 



Assessing Marbled Murrelet Habitat 

 Quality in British Columbia 



Conservation and Management Requirements 



Marbled Murrelets appear to nest in scattered forest 

 locations over a vast area in coastal British Columbia 

 (Campbell and others 1990, Rodway 1990, Rodway and 

 others 1992). There is a growing need to identify and preserve 

 nesting habitat, particularly in the many areas facing clearcut 

 logging. Unlike the situation to the south in the United 

 States, identification of occupied stands has not guaranteed 

 protection in British Columbia because Canada lacks an 

 Endangered Species Act to enforce strict protection of habitat, 

 and neither federal nor provincial governments are likely to 

 block all commercial logging in occupied stands. Only the 

 most valuable nesting habitat is likely to be preserved outside 

 parks, and measures to identify such habitat are urgently 

 needed. At least two categories of forest need to be considered 

 for immediate preservation: areas supporting many breeding 

 birds which make up a significant proportion of the provincial 

 murrelet population; and forest patches supporting remnant 

 populations in areas severely affected by habitat loss. The 

 first is important for maintaining a large, viable breeding 

 population of murrelets and the second to maintain a wide 

 breeding range and genetic diversity. 



Efforts to identify high quality habitat in British Columbia 

 are at a very early stage. The huge areas involved and 

 paucity of resources for surveying murrelets make it unlikely 

 that the intensive multi-year surveys covering 12-30 ha, 

 which are recommended for identifying occupied stands 

 (Ralph and others 1994) will be widely implemented for 

 short term management in British Columbia. As an interim 

 measure, forest and wildlife managers will need general 

 guidelines on the quality of forest stands being considered 

 for logging. Intensive surveys can then be focused on the 

 forest stands with greatest potential as nest sites. 



158 



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



