Chapter 15 



Inland Habitat Suitability for the Marbled Murrelet in 

 Southcentral Alaska 



Katherine J. Kuletz Dennis K. Marks Nancy L. Naslund 



Nike J. Goodson Mary B. Cody 1 



Abstract: The majority of Marbled Murrelets (Brachyromphus 

 marmoratus) nest in Alaska, where they sometimes nest on the 

 ground, and their nesting habitat requirements are not well under- 

 stood. The inland activity of murrelets was surveyed, and habitat 

 features measured, between 1991 and 1993, in Prince William Sound, 

 Kenai Fjords National Park and Afognak Island, Alaska (n = 262 

 sites). We used these data to develop statistical models that explain 

 variation in murrelet activity levels and predict the occurrence of 

 occupied behaviors (indicative of nesting), based on temporal, geo- 

 graphic, topographic, weather, and habitat characteristics. Multiple 

 regression analyses explained 52 percent of the variation in general 

 murrelet activity levels (f < 0.0001). The best model included sur- 

 vey date, location relative to the head of a bay, elevation, slope, 

 aspect, percentage of forest cover, tree diameter, and epiphyte cover 

 on tree branches. The highest activity levels were associated with 

 late July surveys at the heads of bays where there was high epiphyte 

 cover on trees. Stepwise logistic regression was used to identify 

 variables that could predict the probability of detecting occupied 

 behaviors at a survey site. The best model included survey method 

 (from a boat, shore, or upland), location relative to the head of a bay, 

 tree diameter, and number of potential nesting platforms on trees. 

 The best predictors for observing occupied behaviors were tree 

 diameter and number of platforms. In a jackknife procedure, the 

 logistic function correctly classified 83 percent of the occupied 

 sites. Overall, the features indicative of murrelet nesting habitat 

 include low elevation locations near the heads of bays, with exten- 

 sive forest cover of large old-growth trees. Our results were derived 

 from surveys designed to estimate murrelet use of forested habitat 

 and may not accurately reflect use of nonforested habitat. There- 

 fore, caution should be exercised when extrapolating observed trends 

 on a broad scale across the landscape. 



The reliance of Marbled Murrelets (Brachyramphus 

 marmoratus) on mature and old-growth forest for nesting 

 has been well established in the southern portion of the 

 species' range (see Carter and Morrison 1992; Hamer and 

 Nelson, this volume b). Yet, the majority of Marbled Murrelets 

 breed in Alaska, where nesting habitat requirements are not 

 clearly understood (Mendenhall 1992). Offshore surveys 

 suggest that about 97 percent of the population within Alaska 

 occurs offshore of lands with at least some old-growth forest 

 cover (Piatt and Ford 1993). These forested areas extend 

 from southeast Alaska, north along the Gulf of Alaska, and 

 throughout southcentral Alaska. However, the extent of 

 forested habitat is variable in this region. "Forested" areas 

 include unforested habitat, and tree line may extend only 

 200 m above sea level and a few kilometers inland. 



1 Wildlife Biologists, Migratory Bird Management, U.S. Fish and 

 Wildlife Service, U.S. Department of Interior, 1011 E. Tudor Road, An- 

 chorage, AK 99503 



The choice of nesting habitat for murrelets appears 

 superficially to be broader in Alaska, where murrelets nest 

 both in trees and on the ground, than at lower latitudes. 

 Before the early 1980's, only six Marbled Murrelet ground 

 nests had been found (Day and others 1983). Since then, three 

 tree nests have been documented in southeast Alaska, and one 

 nest was found on a tree root overhanging a cliff (Brown, 

 pers. comm.; Ford and Brown 1994; Quinlan and Hughes 

 1990). In southcentral Alaska, 15 tree nests and seven additional 

 ground nests were found between 1989 and 1993 (Balogh, 

 pers. comm.; Hughes, pers. comm.; Kuletz and others 1994c; 

 Mickelson, pers. comm.; Naslund and others, in press; Rice, 

 pers. comm.; Youkey, pers. comm.). The apparent importance 

 of ground nesting by murrelets in Alaska is partially an artifact 

 of effort. Ground nests are more easily discovered than tree 

 nests, inflating their relative numbers. Additionally, it is 

 possible that ground nests of the Kittlitz's Murrelet (B. 

 brevirostris) can be mistaken for those of Marbled Murrelets 

 (Day and others 1983). Therefore, it was unclear how important 

 ground nesting was to the Marbled Murrelet population. 



Following the 1989 Exxon Valdez Oil spill, the protection 

 of habitat was identified as a means of restoring injured resources 

 such as the Marbled Murrelet. Our goal was to provide 

 information on murrelet nesting habitat in the spill zone to 

 guide protection and land acquisition decisions. Between 1990 

 and 1993, we examined aspects of murrelet nesting behavior 

 and habitat use in Prince William Sound and Kenai Fjords 

 National Park (Kuletz and others 1994b, c). Concurrently, in 

 1992, murrelet surveys were conducted on Afognak Island, 

 north of Kodiak Island (Cody and Gerlach 1993, U.S. Fish 

 and Wildlife Service 1993). Although there were differences 

 in study design among the studies, they provided a substantial 

 data base for relating habitat variables to murrelet activity 

 throughout the spill zone. Data from these four studies were 

 combined to develop a broad-based model of murrelet activity 

 in relation to weather, season, and habitat variables that 

 would apply throughout southcentral Alaska. We also 

 developed a statistical model of site characteristics where 

 occupied behavior, indicative of nesting birds, was observed. 



Methods 



Study Area 



The study area encompasses the Naked Island group in 

 central Prince William Sound, western Prince William Sound, 

 the Kenai Fjords National Park, and two parcels on Afognak 

 Island (fig. 1). Brachyramphus murrelets comprise a large 

 portion of the avifauna in these areas. The estimated 

 Brachyramphus murrelet population for Prince William 



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



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