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Document Type

Peer-Review Article

Abstract

In transect butterfly surveys at 40 prairies in Iowa, Minnesota, and North Dakota in summer each year during 1988-1997, we recorded 2403 adults of Poweshiek skipperling (Oarisma poweshiek) at 20 sites, 547 Dakota skippers (Hesperia dacotae) at 12 sites, 27 Ottoe skippers (H. ottoe) at one site, 290 Pawnee skippers (H. leonardus pawnee) at eight sites, and 81 Arogos skippers (Atrytone arogos) at nine sites. In correlations of relative density (individuals/km) of the analyzable species (all but Ottoe skipper), geographical factors (latitude and longitude) produced the most significant correlations, followed by timing (with higher numbers nearer noontime), and lastly weather (positive correlation with temperature, negative correlation with wind speed). The relative densities of these analyzable species showed more significant differences in relation to habitat factors than to variables describing diurnal activity patterns or weather conditions. Relatively higher skipper densities occurred in drier, undergraded prairie vegetation in sites with diverse rather than uniform topography. Patterns of relative density also varied among species with respect to management by idling, grazing, haying, or burning. Nectar visits by species, and by sex if possible, are reported. More instances of courtship rejection than mating were observed. On later dates in the flight period, female Dakota skippers proportionately increased and the sex ratio became more variable. With increasing relative density, the sex ratio of Dakota and Pawnee skippers became less variable and tended to- ward values in the range of about an even ratio.

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