Red squirrels and predation risk to bird nests in northern forests

• Published in: Canadian Journal of Zoology
• Main Authors: Willson, Mary F, Santo, Toni L. De, Sieving, Kathryn E
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 2003
• Subjects: Animal Science and Zoology; Ecology, Evolution, Behavior and Systematics; Yukon; Alaska
• Online Access: http://dx.doi.org/10.1139/z03-096; http://www.nrcresearchpress.com/doi/pdf/10.1139/z03-096

Red squirrels (Tamiasciurus hudsonicus) are important predators on bird nests in northern conifer forests, and previous work has shown that nest density of understory birds is low in these forests compared with deciduous forest. Here, we examine the relationships between the risk of squirrel predation and nest distribution at a smaller, within-habitat scale using both experimental and comparative studies. Female squirrels depredated experimental nests more quickly than males in interior forests near the Yukon – British Columbia border, but after 2 weeks, there was no difference in the percentage of nests depredated by males and females. The density of squirrels and the risk of experimental nest predation increased but the index of natural nest density did not decrease with the density of cone-bearing Sitka spruce (Picea sitchensis) trees in coastal conifer forests of Southeast Alaska. Experimental nests in successional deciduous stands had high risks of predation, in part because squirrels occupied small stands of colonizing spruces in the deciduous matrix and foraged widely in the deciduous stands. In the experimental study site, natural nests occurred at similar densities both next to and away from squirrel-occupied spruce stands, but in other areas, there was a "halo" of low nest density in deciduous vegetation next to spruce stands. Overall, there was little evidence that, within habitats, birds chose nest sites that minimized the risk of squirrel predation.