Habitat associations of adult Oregon Branded Skipper at Cordova Shore, Vancouver Island, British Columbia

Abstract

Oregon Branded Skipper (Hesperia colorado oregonia Edwards), is an Endangered butterfly extant at 6 remaining sites on Vancouver Island, British Columbia. I studied the habitat associations of this subspecies within a coastal sand ecosystem at Cordova Shore on southeast Vancouver Island, British Columbia. Little is known about habitat requirements for this butterfly; however, because of its Endangered status, information on its habitat is required to help direct conservation action. During the summers of 2013 and 2014, I compared habitat conditions at occupied and simultaneously unoccupied sites. I used conditional logistic regression for matched pairs to investigate relationships between butterfly presence and six habitat variables in 21 occupied and 21 random plots and used Akaike information criterion (AIC) to identify the best among a set of 20 candidate models. Most of the butterflies (91%) were observed within the Dune wildrye – Beach pea (Leymus mollis - Lathyrus japonicas) terrestrial ecosystem. The best supported model included black knotweed (Polygonum paronychia) and Oregon gumweed (Grindelia oregonia) as the sole variables predicting the occurrence of Oregon Banded Skipper. The model predicted that the likelihood that Oregon Branded Skipper will be present increases with increases in the cover of Oregon gumweed (OR = 1.5, 95% CI: 0.9-2.6) and black knotweed (OR = 1.6, 95% CI: 0.1-23.6). The two plants are likely important for the Skipper; however, small sample sizes and model confidence intervals suggest a cautionary approach to applying the model. In light of these findings, I provide guidance for future conservation of Oregon Branded Skipper to land managers within Cordova Shore.