UBC Theses and Dissertations
Patterns of nest predation and nest predator abundance in a fragmented englemann spruce/subalpine fir forest Campbell, Victoria Elizabeth Anne
In a fragmented Englemann Spruce/Subalpine Fir (ESSF) forest, I used artificial nests to test the hypothesis that nest predation is greater at the forest edge and in clearcuts, than in the forest interior. In this forest type, nests in clearcuts had a lower frequency of predation than nests in the forest, yet there was no consistent difference in the frequency of predation at the forest edge or in the forest interior, a pattern opposite to that previously documented. However, in previous studies the landscape was fragmented by agricultural development, where populations of potential nest predators may be elevated as a result of anthropogenic food sources. I found no evidence that the decrease in the frequency of predation on nests in clearcuts was the result of a concomitant shift in the identity (from plasticine eggs) and/or number of predators (from predator surveys) in these locations. Rather, in habitats fragmented by logging activities, many nest predators may avoid foraging in the clearcut because of the increased predation risk to themselves in these locations. In addition to the effect of nest location on predation rate, there was marked temporal variation in the frequency of nest predation. I documented an increase in nest predation both within and between trials; and this may have been a result of predators learning to exploit artificial nests. Studies which can identify individual predators, and record their foraging activity in response to artificial nests, may shed light on the mechanisms behind this temporal variation in nest predation. While artificial nests provide an index of predation risk, future use of this method must be cautioned against until the biases can be clearly identified. Further study of the patterns of nest predation in fragmented habitats should instead focus on the patterns of nest predation on natural nests, the distribution and abundance of potential nest predators in fragmented and undisturbed forest habitats, and on how nest predators forage within clearcut, forest edge, and in forest interior habitats.