Robert Dahlgren | USGS Science

USGS1995

Biota of the upper Mississippi River ecosystem

The Mississippi River is one of the world's major river systems in size, habitat and biotic diversity, and biotic productivity. The navigable Upper Mississippi River, extending 1,370 km (850 mi) from St. Anthony Falls (Minnesota) to the confluence with the Ohio River, has been impounded by 27 locks and dams to enhance commercial navigation. The reach between two consecutive locks and dams is termed a "pool." The upstream portions of many pools are similar to the unimpounded river, whereas the downstream reaches are similar to reservoirs.

Upper Mississippi River↗

USGS1979

Prairie dog distribution in areas inhabited by black-footed ferrets

The distribution of black-tailed prairie dog ( Cynomys ludovicianus ) towns was delineated in a 1490 km 2 study area in Mellette County, South Dakota, and was examined to determine the characteristics of black-looted ferret ( Mustela nigripes ) habitat. Between 1964 and 1974, black-looted ferrets were observed on 14 prairie dog towns in this area. Eighty-six prairie dog towns, located throughout the study area, were not randomly distributed; towns were paired or clumped in spatial distribution. Mean distance between a town and its nearest neighbor was 2.4 km; mean distance between a ferret-occupied town and the nearest town was similar, 2.7 km. Management recommendations are to maintain at least eight towns per township, each at least 12 ha in size. Of these eight towns, two or more should exceed 40 ha.

South Dakota↗