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COSEWIC Assessment and Status Report on the Eastern Persius Duskywing in Canada

Limiting Factors and Threats

The most important factor limiting the size and distribution of E. p. persius populations is the quality and distribution of its breeding habitat. The skipper almost always occurs in savannah and prairie habitats with populations of wild lupine or wild indigo, although specimens are sometimes taken in other habitats. Disturbance (natural or through management regimes) is needed to ensure the health of open woodland and prairie communities, but large-scale and high intensity fires may destroy all E. p. persius populations in an area. Fire suppression and tree planting have certainly had devastating effects on E. p. persius populations through successional habitat change and the resultant decline in natural lupine populations. Increased isolation of host plant patches through human-induced or natural processes (e.g., forest succession, creation of dispersal barriers through industrial or urban development) likely had direct negative consequences for E. p. persius.

Superabundant deer populations are also thought to cause declines in host plants through extensive herbivory. The requirements of this skipper for specific plant species that are themselves rare and occur in isolated, fragmented patches is the biggest problem faced by the butterfly.

Natural factors likely to influence individual survivorship include parasitoids and predators (although none are specifically known to attack E. p. persius), and such density independent factors as fire, desiccation, weather and even incidental browsing by deer. Due to the dynamic nature of the habitat in which this skipper is found, it is likely that individual survivorship is low and is influenced by natural habitat change and disturbance by fire. In the past, populations survived by dispersing to other areas of suitable habitat, but when alternate pockets of suitable habitat became unavailable, the likelihood of individuals escaping hostile conditions to reproduce elsewhere declined.

Anthropogenic factors affecting survivorship include insecticide spraying and indirect factors that affect the species' habitat, including fire suppression, and facilitating the growth of deer populations and the colonization of invasive plant species. The spraying of insecticide to combat the Gypsy Moth (Lymantria dispar (L.)) is thought to have been responsible for the substantial decline in E. p. persius populations in the 1950s, and modern spray programs could eliminate any remaining populations that may be in the sprayed areas (NatureServe Explorer 2001). The drought of 1988 in combination with spraying of Bacillus thuringiensis (Bt) at St. Williams may have eliminated what must have been an already small population of E. p. persius, if it indeed had survived to that time (Peter Carson, pers. comm., 2002). Indirectly, humans have also modified the habitat by suppressing fire, which has allowed woody plants to colonize, creating an environment that inhibits the survival and growth of the host plants. The elimination of the natural predators of white-tailed deer in southwestern Ontario and the change in landscape structure has caused this herbivore's population to grow significantly, which has placed a large amount of pressure on lupines and other herbaceous plants within the prairie and savannah habitats of southern Ontario.