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UBC Theses and Dissertations

Population ecology and resource limitation of northern flying squirrels and Douglas squirrels Ransome, Douglas B.

Abstract

Habitat preferences and population dynamics of northern flying squirrels (Glaucomys sabrinus) and Douglas squirrels (Tamiasciurus douglasii) were examined in old-growth and mature second-growth stands in British Columbia, Canada. Using mark-recapture techniques to estimate population dynamics, I tested the hypothesis that old-growth stands provided higher quality habitat than second-growth stands for these species. Populations were monitored in two old-growth and two mature second-growth stands from August 1995 to May 1999. There were no differences in movement, density, recruitment, weight of males, survival, percentage of the population breeding, and the duration that individuals remained on the study plots between stand types for G. sabrinus. Similarly, with the exception of recruitment, there were no differences in these parameters between stand types for T. douglasii. Recruitment of T. douglasii was higher in second-growth than old-growth stands. Old-growth stands were not higher-quality habitat than second-growth stands for either species for the period of enquiry and the parameters I measured. Population dynamics of G. sabrinus and T. douglasii were also examined in thinned and unthinned stands. I tested the hypothesis that unthinned stands provided higher-quality habitat than thinned stands for these species. Populations were monitored using mark-recapture techniques on two thinned and two unthinned stand from August 1995 to May 1999. Commercial thinning was initiated 9 and 7 months following the first trap session. There were no differences in movement, density, recruitment, weight of males, survival, percentage of males breeding, and the duration that individuals remained in thinned and unthinned stands for G. sabrinus and T. douglasii. Unthinned stands were not higher-quality habitat than commercially-thinned stands for either species for the period o f enquiry and the parameters I measured. Finally, effects of food and den site supplementation on the population dynamics of G. sabrinus and T. douglasii were examined in mature second-growth stands in British Columbia, Canada. I tested the hypothesis that populations of these squirrels were limited primarily by abundance of food, not den sites. The experimental design included a randomized complete block design with three replicates and four treatments (food supplementation, food and nest box supplementation, nest box supplementation, and control). Populations were sampled intensively from June 1996 to March 1999. There were no differences in movement, density, recruitment, weight of males, percentage of males breeding, and the duration that individuals remained on the grids among treatments for G. sabrinus and T. douglasii. However, survival of G. sabrinus decreased significantly from pre- to post-treatment periods in stands without food supplementation. When food was added, survival increased significantly or remained unchanged. In addition, occupancy rate of nest boxes in stands supplemented with nest boxes and food was 6- to 12- times higher (1998 - 88.4%, 1999 - 75.0%) than in stands with nest boxes only (1998 - 7.0%, 1999 - 12.2%o). G. sabrinus occupied the majority of the nest boxes. Nest boxes in stands supplemented with food primarily contained covered nests (76.5%) while beds dominated (68.3%) those in stands supplemented with nest boxes only. I concluded that G. sabrinus readily used nest boxes but their populations were not limited by the availability of den sites; availability of food appeared to limit their populations. Populations of T. douglasii were not limited by the availability of food or den sites during my study.

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