7393 - Laserfiche WebLink

Home Browse Search

The Unportance of these questions is obvious. If the relationship between flow and streambed characteristics is understood, then water allocated for instream purposes can be used in the most efficient way. The fact that the decline in channel width since 1938 has been twice the loss before 1938 suggests that Lake McConaughy and the increment in consumption it permitted have had a decisive effect on channel width, an argument that of course assumes a fairly rapid response of channel width to stream flow. Some lUnited evidence for this assumption is provided by an analysis of the age of cottonwoods in what used to be the channel of the river. The oldest trees date from the tUne of the closing of the dam. 4. Because the cranes will roost only on open sandbars, the encroachment of vegetation will reduce the suitable roosting area. As noted, whooping cranes and sandhill cranes are likely to spend up to 6 weeks in the critical habitat area during the spring, gaining strength for the second half of their migration. As noted above, the FWS claims that the cranes' preferred roosting sites during this period (and indeed, generally) are sandbar islands, espe- cially those free of tall vegetation. Presumably, this is required for pro- tection from predation. The cranes also rely on the wetland habitat for food production (their diet is principally crustaceans). Obviously, the reduction in channel width will greatly decrease the availability of such areas. 5. A reduction in the roosting area suitable for cranes will either cause crowding, causing stress and increasing the chances of catastrophic disease outbreaks, or force the cranes to seek alternative roosting sites in the Cen- tral Flyway, which is not available. Migration is a very stressful and danger- ous period for the whoopers, and habitat modification can only make it more so. According to the FWS, the whooper death rate during the winter at Aransas National Wildlife Refuge is about 0.05 birds per month. During the rest of the year--while in migration or spending the sumner at Wood Buffalo National Park--the death rate is about one bird per month. Indeed, 66% of all known whooper losses have occurred during migration. The likely response of whooping cranes to a loss of suitable habitat along the Platte is not well understood. At present, in fact, little is known gen- erally about the migration behavior of the cranes. While it is known that the whoopers migrate not as a flock but in small family groups, it is not known whether they stop every year. It is suspected, however, that the Platte may 39