A first step towards successful conservation: understanding local oviposition site selection of an imperiled butterfly, mardon skipper

Lack of basic biological information is a key limiting factor in conservation of at-risk butterflies. In the Puget prairies of Washington State little is known about the habitat requirements of mardon skipper (Polites mardon, federal candidate, WA endangered). We investigated oviposition site selection and used our results to assess oviposition habitat quality at a restored site with reintroduction potential. During the 2009 flight season we marked eighty-eight eggs and sampled vegetation at oviposition and random locations, measuring habitat variables with respect to the oviposition plant, vegetation structure, and vegetation cover. Eighty-six of the eighty-eight eggs were laid on Festuca roemeri, a native, perennial bunchgrass. Discriminant function analysis revealed selection of oviposition sites based on habitat structure; females laid eggs in small F. roemeri tufts in sparsely vegetated areas of the prairie. These results are contrary to results from a previous study in the Cascade Mountains of WA where females are generalists and selected densely vegetated areas, suggesting that the species has geographically specific habitat requirements. To assess oviposition habitat at a potential reintroduction site we measured the six variables most important for oviposition at the occupied site and a proposed reintroduction site. Results revealed differences in habitat quality between locations and suggest a need for further habitat management at the reintroduction site. Our results highlight the importance of understanding the local habitat use of a rare species where restoration activities occur and increase our ability to target habitat management where it is most needed for the persistence of the species.