Ecology and Status of Greater Sandhill Cranes in Southeastern Wisconsin

Abstract

The population and ecology of greater sandhill cranes was studied in 17 southeastern Wisconsin counties during 1976 and 1977. A population of 1,106 adult cranes was censused, of which 52 percent consisted of breeding pairs and the remainder non-breeding flocks numbering 5 to 90 birds. Ninety-two percent of the population was located in 4 counties. The population has increased substantially since 1930. Over 78 percent of the crane population occurs on privately owned wetlands which are currently subject to an annual rate of wetland drainage exceeding 3 percent. The average size wetland used by cranes was 126 ha and a significant preference was exhibited for wetland Types 2, 3, and 8. Significant correlations (r=0.72) between wetland size and years of crane occupancy indicated that intensive pioneering into formerly unoccupied habitat has occurred. Fifty-three crane nests were found, most in cattail communities along sedge-cattail ecotones. The highest nest densities occurred on wetlands with floating bog mats. Mean clutch size was 1.91 eggs and the mean hatching date was 10 May. Hatching success was 84 percent and the fledging rate of chicks averaged 69 percent. Cranes preferred cattle pastures for brood rearing habitat. The mean size of 7 territories was 38 ha. The average brood size at fledging was 1.36 chicks/nesting pair and the annual recruitment .rate was 11.1 percent. Crane roosts consisted of ponds 1.4 ha in size, 5-27 em deep, surrounded by tall emergent vegetation. Peak arrival of cranes at roosts occurred during the first 15 minutes after sunset and peak departure was 5 minutes before to 30 minutes after sunrise. Thirty-seven cranes were banded and 136 observations were made on color-marked cranes within the study area. Nonbreeding cranes fed primarily on the tubers of aquatic plants in spring and almost exclusively in grain fields after July. Only 5 percent of the farmers adjacent to wetlands occupied by cranes reported significant crop depredations. A peak migratory population of 2,400 cranes was censused on 7 major staging areas on 20 September 1977. Current management recommendations involve the preservation of scattered wetland units in each county identified as optimal crane nesting habitat.