Phenology, Movement, and Population Size of an Endangered Butterfly, the Mottled Duskywing (Erynnis martialis)

Abstract

Extant populations of the mottled duskywing (Erynnis martialis), an endangered butterfly in Canada, occur in Ontario and Manitoba but there are no estimates of population size, and limited knowledge of phenology and movement. We conducted spatially explicit mark-re-sighting over multiple years at two of the largest known populations in Ontario (specific locations withheld). Population sizes at Site A were estimated to be 795 individuals (CL = 617 – 1024) in 2019 and 1165 individuals (849 – 1598) in 2021, while estimates at Site B were 360 (252 – 513) in 2019 and 722 (542 – 961) in 2020. High densities of adults were generally associated with high Ceanothus abundance and mixed and open canopies, but relationships varied by site and year. Eighty percent of adult movements were within 500 m and peak abundance ranged from June 8 – 30. Our work provides valuable information for future management and recovery efforts, including planned translocations in Ontario.