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any season. Each pileated woodpecker had several roost trees and usually flew directly to another roost if disturbed or if a roost was occupied. Cavity use was high as determined by observed evidence, particularly for deep and hollow cavities, but 22.3% of cavities were empty when inspected, and empty cavities were present throughout the year. However, empty cavities did not necessarily imply nonuse, because pileated woodpeckers and SCU used empty cavities without leaving evidence, and they also removed evidence of use from cavities. Cavity occupancy was low, and I did not observe any direct competition between species for cavities. Considering all evidence, I believe that there was a surplus of pileated woodpecker cavities available for SCU use in the study area during all seasons. Cavities excavated by pileated woodpeckers were associated with a high diversity of cavityusing species. Pileated woodpecker cavities were used or probably used by 61% of 38 cavityusing vertebrate species in the study area. Three of 16 cavity-using vertebrate species that did not use pileated woodpecker cavities were too large to enter them and 10 other species were uncommon in the study area. At least 38 species of vertebrates are known to use pileated woodpecker cavities (Hoyt 1957, Ehrlich et al. 1988, Bull and Snider 1993, McClelland 1977, Bull and Jackson 1995, this study). The next largest reported SCU community for a North American PCE was 24 species associated with red-cockaded woodpecker (Picoides borealis) cavities (Conner et al. 1997). Many species that used red-cockaded woodpecker cavities did so only after they had been enlarged by pileated woodpeckers (Conner et al. 1997). Collectively, cavities of other PCE occurring in my study area were used by at least 13 SCU (R. L. Bonar, unpublished data). Many SCU that can enter smaller cavities also used pileated woodpecker cavities, which are larger, deeper, and often higher above ground than other PCE cavities in the study area. Large entrances and cavity volume make pileated woodpecker cavities accessible to more species than smaller cavities excavated by other PCE. Large cavities can increase reproductive success and reduce predation risk (Moed and Dawson 1979, Rendell and Robertson 1989, Li and Martin 1991), and may provide thermoregulatory advantages for some species, including northern flying squirrels (Carey et al. 1997). Conversely, large entrances may actually increase predation risk and competition for cavities (Moed and Dawson 1979). Use of pileated woodpecker cavities by SCU may also have been influenced by the availability of other cavities and by selection criteria and other habitat characteristics of SCU. I found evidence to support McLaren’s (1963) concept of a large cavity web based on pileated woodpecker cavities. Pileated woodpeckers produce large cavities, which were used by 4 large SCU: Barrow’s goldeneye, common goldeneye (B. clangula), boreal owl, and American marten (Martes americana). As these species are too large to enter most other PCE cavities, they depend on either pileated woodpecker cavities or large natural cavities. My results also support the concept of a cavity web structured around cavities as a central resource (Martin and Eadie 1999). Based on cavity size, the pileated woodpecker cavity web provides a critical resource for large SCU when natural cavities are rare, as they were in the study area. Smaller species also used pileated woodpecker cavities, indicating probable linkages between the pileated woodpecker cavity web and webs based on smaller PCE cavities. MANAGEMENT IMPLICATIONS Pileated woodpecker cavities are an important resource for the cavity-using wildlife community and may be a critical resource for some large SCU in boreal forests. On that basis, pileated woodpeckers are a keystone species, with an essential functional role in maintaining the cavity-using wildlife community in boreal forests. Further research on species-specific cavity selection and use would help to determine functional relationships between PCE and SCU. While there may have been a surplus of pileated woodpecker cavities in this study, potential increases in losses from fires, logging, and other disturbances could interact to reverse the current situation. It could take many years to replace lost cavities because of low rates of cavity production. As pileated woodpecker cavity trees can persist as a cavity user resource for many years, perhaps several decades, forest managers should attempt to identify and protect existing 59

Pwp 2001 04 rpt phdthesis pileatedwoodpeckerhabitatecologyinabfoothills  
Pwp 2001 04 rpt phdthesis pileatedwoodpeckerhabitatecologyinabfoothills  

http://foothillsri.ca/sites/default/files/null/PWP_2001_04_Rpt_PhDThesis_PileatedWoodpeckerHabitatEcologyinABFoothills.pdf

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