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The Marbled Murrelet is a seabird of conservation concern that nests in large, mossy branches of old growth trees (Ralph et al. 1995). Documentation of population declines in locations throughout its breeding range (Klosiewski and Laing 1994, Kelson et al. 1995, Strong 2003) has created concerns regarding the demographic consequences of continuing harvest and fragmentation of old-growth habitat (Burger 2002). The establishment of adequate habitat reserves of terrestrial habitat has been proposed as a management priority to ensure sustainable populations of murrelets (Burger 2002, McShane et al. 2004). However, this process has been hampered by the uncertainty regarding the relative value of different size patches of forests for nesting murrelets. Small forest patches may be less productive due to their high proportion of edge habitat, which is often subjected to higher rates of nest predation (Paton 1994, Batáry and Báldi 2004, but see Lahiti 2001). Nest predation may be elevated at edges if predators such as corvids preferentially use edges as travel lines (Andrén 1995), forage disproportionately along edges due to higher densities of prey (Gates and Gysel 1978), or if nests at edges have higher risk of predation due to lower nest-site cover (Ratti and Reese 1988). Edges may also be detrimental to nesting murrelets as a result of less hospitable microclimate regimes found in these habitats (Burger 2002, McShane et al. 2004). Increases in temperature and solar radiation at edges may cause thermal stress or dehydration in murrelet chicks at clearcut edges (Binford et al. 1975), or reduce the growth and recruitment of mossy nesting platforms. However, the evidence is equivocal as to whether small patches and forest edges actually negatively impact murrelet productivity. While some researchers have found samples of successful nests to be significantly farther from edges than failed nests (Nelson and Hamer 1995, Manley 1999), others have found no significant difference in nest success between nests adjacent to or far from edges (Bradley 2002; Zharikov 2006, 2007). In addition, murrelets appear to nest disproportionately near both natural edges such as streams and avalanche chutes, as well as anthropogenic edges such as clearcuts and regenerating forest (Nelson and Hamer 1995, McShane et al. 2004, Zharikov et al. 2006, 2007). This seemingly paradoxical preference likely reflects a requirement of this heavily wing-loaded bird for safe access to nest sites for adults, and clear flight paths for fledgling chicks (Manley 1999). This observation highlights the importance of determining the extent of edge effects on murrelets, as a preference for edges may be maladaptive in industrially fragmented landscapes. We are currently investigating the local and landscape-level factors that influence the presence of edge effects for Marbled Murrelets. These data will be used to refine policies for recognizing the potential value of existing areas of habitat and for guiding the selection of additional areas.
David B. Lank.
Lank, David B.. 2007. MaMu Habitat - SFU Edge E. Forest Investment Account (FIA) - Land Base Investment Program - Innovative. Forest Investment Account Report
Topic: FLNRORD Research Program
Keywords: Forest, Investment, Account, (FIA), Marbled, Murrelet, British, Columbia
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