Avian nest survival and snake abundance in restored and remnant grasslands in northwestern Iowa
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Intensive agriculture in the Midwest has drastically reduced the amount of grassland on the landscape. Today less than 0.1% of the pre-settlement prairie remains. Consequently, native wildlife populations have declined. In recent years federal initiatives such as the Conservation Reserve Program and the North American Waterfowl Management Plan (now part of the North American Bird Conservation Initiative) have responded to these declines by providing incentives for large scale restoration of perennial grassland. Little is known, however, about how restored habitats function compared to remnant grasslands. I studied the impacts of restoration on grassland birds and snakes in northwestern Iowa though two distinct, though interconnected questions. First, I compared avian nest success on restored and remnant grasslands. During the 2003 and 2004 breeding seasons, I located nests in 10 restored and 6 remnant grasslands. Survival estimates were compared to examine the impact of current restoration efforts on local bird productivity. Dickcissels (Spiza americana), Bobolinks (Dolichonyx oryzivorus), Red-winged Blackbirds (Agelaius phoeniceus) and Clay-colored Sparrows (Spizella pallida) nested in both habitat types. We used logistic-exposure models and AIC model selection to examine variation in daily survival rates. The effect of habitat type was relatively weak, indicating restored grasslands in highly fragmented agricultural landscapes can provide comparable habitat for grassland-breeding birds, even if the restoration efforts do not mirror native habitat conditions. Second, I compared snake abundance within 100m of a gravel road to abundance in the interior of restored grasslands. Through the use of artificial shelters, we captured 694 individuals of four species during 16 survey weeks. Sixty-six percent of the captures were plains garter snakes (Thamnophis radix). We found no significant difference between interior and edge snake abundance, indicating that grassland snake abundance is not influenced by road edges at the scale we measured. Results from this study will help guide future efforts to develop high-quality habitat for grassland birds and snakes in agricultural landscapes.