WSP00190 - Laserfiche WebLink

Home Browse Search

SECTION THREE Whooping Crane I I I I I I , I I 1 I I activities within the migration route; increased shooting of birds and collecting of eggs. The impact of man's conversion of pothole and prairie throughout North America to crop production, and the species sensitivity to disturbance, made nearly all of the whooping cranes original range unsuitable for use by the species. Disruptive practices included draining, fencing, plowing, sowing, cultivation, harvesting, and human activities associated with these operations (FWS 1994). In the specific case of the Platte River, water depletions appreciably reduced migrational habitat by adversely altering the open channel roosting and wetland feeding habitats that whooping cranes requiTe. Several biological characteristics of the whooping crane such as delayed sexual maturity, small clutch size, and low recruitment rate preclude rapid population recovery. The short ice-free season (4 months) on the current breeding grounds may also be a handicap to productivity. The traditions that saved the whooping crane as a small relict breeding population in Wood Buffalo National Park also prevent its voluntary re-colonization of its former breeding area. Most mortality of fledged birds occurs between their leaving Aransas in the spring and returning in the fall (Lewis et aJ. 1992). During the 1938-1993 period, 217 adults and subadults disappeared or were found dead during the April to November period. During the same period, the known losses of over-wintering whooping cranes totaled 49. Thus, about 82 percent of the losses of the Aransas-Wood Buffalo population occurred during the April to November period and 18 percent during the winter. Drewien et al. (1989) reported that 76 percent of the mortality of fledged birds in the experimental Rocky Mountain population occurred during migration. Powerline collisions are a significant factor affecting long-term recovery of whooping cranes (Howe 1989). Since 1956, 19 whooping cranes have reportedly struck powerlines, accounting for 25 percent of the losses in the Aransas- Wood Buffalo flock (Morkill and Anderson 1990) and 40 percent in the cross-fostered Rocky Mountain flock (Brown et al. 1987). Lewis (1988) cited powerline collisions as the number one identified cause of mortality in fledged whooping cranes, and Kuyt (1992) stated that collision with powerlines was the most serious threat to migrating whooping cranes. Unmarked transmission lines, such as those crossing the Platte River near roosting habitat, are potential collision sites. There are no records of whooping cranes striking powerlines crossing the Platte River, but it is also unlikely that a dead or mortally injured bird would be found. Because sandhill cranes (Grus canadensis) have flight characteristics and size similar to whooping cranes, they can be used as a surrogate in studies of the effects of powerlines (Faanes and Johnson 1992; Ward and Anderson 1992). Studies indicate that sandhill crane strikes on powerlines can be reduced by 40 to SO percent by marking pertinent spans (Morkill and Anderson 1990). These results can be applied in marking powerlines in areas consistently used by whooping cranes (Lewis 1990). Because most birds disappear with no indication of cause of mortality, the role of predation during migration is difficult to determine. Allen (1952) identified some of the potential predators of sandhill cranes to be wolves, foxes, coyotes, dogs, raccoons, eagles, and great horned owls. Wolves, coyotes, and golden eagles have been observed killing juvenile whooping cranes (Johnson and Temple 1980). Raccoons killed a whooping crane in an enclosure at Baraboo, Wisconsin in June 1982 (Doughty 1989). Lewis (1974) reported that coyotes appear to disturb sandhill cranes at both feeding sites and roosts, making them more wary. Lewis (1996) also IIltSIJ1U1er ~a,tIe . 3-2 "F00972S6OO1~.doc &o;Jl999(9.S2AM)lURSGWCFSi2 fedenlSllhlWlS