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1585 last longet rhan rhe average annual high flow on the river) temporarily eliminates and may limit resident small mammal populations in the flood- plain. Almost all wildlife species are negatively impacted by unexpected. sustained, and large changes in flows that come at critical points in wildlife life cycles. For example, birds rhat nest on sand and gtavel bars during early spring can be disrupted by unexpected inctease in flow that are large enough to inundate these habitats. Fish rhat spawn in backwater areas can be severely impact- ed by flows which are not high enough to inun- date these areas during spawning periods. While mmy nacurJ.l events. such as thundersmrms and rain-an-snow events, can drasr1caJly change Haws, they are typically of a short duration and provide rhe type of flood disturbance thar can be bendl- cial for wildlife species. Converselv, reservoir releases that produce flows ourside the hisroric range of flows for extended periods of time can disrupt ctiticallife stages of wildlife species. The species and life stages rhat are impacted depend upon the exact timing and magnirude of the reservoir releases. Flow-dependent phenomena that can negatively impact waterfowl include damage co nests from dramatic Water level fluctuations, removal or inundation of food sources by severe flooding, and desiccation of water-dependent insects and vc:O'c:racion that serve as food sources when flow is ~ reduced. Certain species. such as wood ducks, require flooded woodland areas for a portion of rhe year, and tlow regime that removed peak flows that create these areas would be detrimental. For captors, the continued viabili[}'" of riverine cononwood-willow riparian sires is extremely important, because rhey provide roosting and nesting sires. A viable fish population is critical 'CO raprors as a food source, and flow fluctuations that drive small mammal prey species from the riparian corridor would be detrimental. Similarly, some shorebird species, such as blue herons, rely upon viable riverine cottonwood-wil- low riparian are:1S. Shorebird species are even more sensitive to flow variations and flooding of riparian are3S, because they are dependent: on areas such as mud flats, shallows, and gravel bars for feeding purposes. Some shorebitd species. such as avocets. also nest in these habitars. so unexpected flood events can severely impact their populations. The spring and sum met bteeding period of amphibians and reptiles makes rhem especially vulnetable ro dtamatic changes in river flow that affect sidewaters and backwaters. For examples, reptiles and amphibians can be negatively impact by reservoir releases of excessively cold water thar invade sidewarers and backwarers, because rhey will not feed or breed in water temperarures of less than 50 degrees. b. Reservoirs Wildlife management agencies recognize chat reservoirs are noc constructed co supporc opcimal wildlife values. However. long term operations have been somewhac: consistent, so cerrain wildlife species have adapted ro and use the habitats sur- rounding the impoundments. Accordingly. signifi- cmr modification of reservoir operations away from historic practices that could impact these habitats will, in rum, have an impact on wildlite populations. At Pueblo Reservoir, maintaining a full pool for a longer period of time during the growing seJ5on. would benefir riparian values. which would, in rum, bendlt wildlife populations. However. maintaining a full pool for a longer time during the growing season could be negative for the fish population, and many wildlife species depend on rhe fish population as a food source. Finally. rhe basin-wide impact of reservoir levels must be considered. If large releases are requited from rhe uppet reservoirs ro maintain Pueblo water levels. the negative effects on Turquoise Reservoir and Twin Lakes wildlife populations may outweigh the gains at Pueblo Reservoir. 4. Water Prefetences for Recreation a. Arkansas River The upper Arkansas River is rhe most intensively used river in the United SCJ.tes for whicewater 33