Spatial segregation of male and female Macoun’s Arctic butterflies (Oeneis macounii) in Riding Mountain National Park, Manitoba: Consequences for conservation

Background/Question/Methods

Knowledge of habitat selection in breeding biology is essential information in conservation planning.  Habitat association and life history of male and female Macoun’s Arctic butterflies, Oeneis macounii, were studied in Riding Mountain National Park (RMNP) in Manitoba, Canada, in the summer of 2011. O. macounii, a satyrine boreal butterfly, is a biennial species found almost exclusively in Canada. The population found in RMNP is disjunct and potentially genetically unique, and has been declining. This project aimed to gather ecological information on the little known Macoun’s Arctic in order to recommend conservation strategies for park biologists. Surveying took place on the Brule Trail (UTM: 437290 5614550). Line transect routes were established through Jack Pine forest and prairie openings and walked daily in order to estimate butterfly abundance and capture individuals. Butterflies were captured, marked and released; GPS coordinates of all capture points were recorded. Wing wear, weight, sex and forewing length were also recorded for each specimen. Upon resighting butterflies, movements between captures were estimated from GPS coordinates. Habitat was assessed in each of fifty 25x25m plots throughout the field site. Habitat variables measured included tree cover, grass cover, elevation, and abundance of many wildflower species.

Results/Conclusions

Throughout the adult flight (18 Jun to 12 July), 61 O. macounii (31 male, 30 female) were captured and marked; 12 individuals were recaptured. Only 4 other individuals were observed at other locations despite extensive surveys. This suggests that the population in RMNP is very small and at risk of extirpation. Generalized additive model analysis was completed using SAS 9.2 software on male and female butterfly abundance within the established plots. This analysis of butterfly occurrence in relation to habitat characteristics showed male butterflies are more abundant in heavy tree cover, and can be described with the model Males = -0.31+0.03(%Tree Cover). Female butterfly occurrence could not be significantly described by any of the habitat characteristics, but were anecdotally noted to occur more frequently in open grassy areas. Butterfly abundance and vegetation were plotted using ArcGIS version 10 software. The difference in habitat requirements for the sexes in O. macounii show that at RMNP, two different habitats must be preserved in order for the population to be maintained. Mature Jack Pine forests where mating occurs and open prairie patches with grasses for oviposition are both necessary for the persistence of O. macounii at Riding Mountain National Park.