An analysis of northern goshawk prey preferences by biogeoclimatic subzone across coastal British Columbia

Abstract

This thesis investigates the dietary preferences of northern goshawk populations in second growth stands on Vancouver Island and the islands of the Johnstone Strait region on the BC Mainland Coast. Prey abundance was inferred through the analysis of pellets composed of regurgitated non-digested prey remains that were collected during the annual survey monitoring program carried out by Mosaic Forest Management and predecessor companies since 2012. The relative abundance of prey species was compared across three Coastal Western Hemlock subzones (CWHvm1, CWHmm1, CWHxm2) under the Biogeoclimatic Ecosystem Classification (BEC) system using the Chi-square test. No significant correlations were found between prey species abundance and BEC subzone (χ2 = 2.3, P = 0.32) in 2013 and (χ2 = 0.84, P = 0.66) in 2014. Trends within the dataset indicate coastal northern goshawks on Vancouver Island and the BC Mainland Coast show a general dietary propensity towards avian prey, which is consistent with findings from other studies. The variation in prey abundance and species diversity reported in this study is more likely a function of topography and forest structure, season and region than it is to BEC subzones. Findings from this study highlights how younger stands could be providing more suitable habitat than was traditionally thought.