Road mortality of dragonflies (Odonata) in a Great Lakes coastal wetland

Although road mortality of vertebrates has been well studied, road mortalit y of invertebrates has rarely been studied or considered in management scen arios. Mackinac Bay is an extensive coastal wetland in northern Michigan. I t is bordered by a two-lane paved highway that separates the marsh, where d ragonflies defend territories and breed, from the adjacent forest where dra gonflies forage and rest. During mid-summer of 1997, daily collections of d ragonfly corpses from the road and road edge were used to estimate daily mo rtality rates and sex ratios among casualties. Daily mortality was highly v ariable, ranging from 10 to 256 casualties per kilometer. Sex ratios among casualties were generally male-skewed (60% or higher). Life-history differe nces between the sexes present a parsimonious explanation for male-specific mortality. Mortality was even or female-skewed fdr some species, and impac ts of road mortality may be more severe in populations where mortality is f emale-skewed. More research about the effects of roads on dragonflies is wa rranted because dragonfly populations are small relative to many invertebra tes and are restricted to wetland habitats which are being degraded or dest royed in many regions.