| Abstract | I studied one primary cavity-nesting bird (northern flicker: Colaptes aurafus) and two secondary cavity-nesting species (mountain bluebirds: Sialia currricoides and tree swallows: Colonizing clear-cuts in the Beaverfoot Valley, Rocky Mountains British Columbia, Canada. The study area was fragmented by industrial forestry leaving 70 clear-cut patches surrounded by mature forest. I used this spatial arrangement of patches to examine the demographic patterns of cavity-nesting birds in relation to habitat parameters. Experimental addition of nest boxes to the interior and edges of patches (i) increased the breeding density of the two secondary cavity-nesters. and (ii) increased the age range of habitat patches occupied. However, the experiment did not result in increased species richness. and no pairs occupied edge boxes. Mountain bluebirds tended to nest one pair to a patch. and I demonstrated the presence of non-breeding 'floater' mountain bluebirds, despite unoccupied nest sites in the area. Both species appear to make habitat selection decisions based on availability of nest sites. as well as vegetation structure characteristics and intra-specific cornpetition.Rates of nest predation for ail species were high, and varied with the successional age of patches. Predation was higher in early successional patches than in older patches. Experiments using artifical eggs rnirrored results from real nests and showed ihat potential predators visited nests in young patches more frequently than in older patches. Additionally, artificiai egg experiments demonstrated that nests on patch edges were visited more frequentiy than those in the intenor of patches.I consuucted a population model based on demographic data for the mountain bluebird incorporating the observed habitat-specific variation in predation rate. With the frequency of different quality patches sirnilar to that observed in the Beaverfoot Valley, the model predicts population size will increase. This outcome. however, is highly dependent on adult and juvenile survival parameters. Finally, I suggest that cavity-nesting birds may be especially vulnerable to current land-use practices. I discuss the implications of my research for forest practices and recommend that adaptive management is crucial to the future success of land management and biodiversity conservation. |
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