River-dependent bird species as potential indicators of ecosystem response to removal of dams on the Elwha River, Washington Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/9c67wq84h

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  • If two dams on the Elwha River are removed, the ecosystem will be open to the downstream flow of sediments and the upstream flow of marine nutrients in the form of anadromous fish. Nutrient enrichment may influence trophic dynamics of the entire ecosystem, extending beyond the aquatic boundary. I assessed the current relative densities of five river dependent bird species on the Elwha and three other rivers in Olympic National Park in Washington State to describe pretreatment reference conditions as a basis for assessment of post-treatment ecosystem responses. I also compared the amount of time that non-breeding and failed-breeding (NBIFB) female Harlequin Ducks (Histrionicus histrionicus) spent foraging on different rivers and on adjacent coastal habitat to determine whether time spent foraging could be used as an indicator of habitat preference. Surveys of key river-dependent bird species were conducted on two rivers in 1996 and on four rivers in 1997. The benthivorous foraging guild was represented by the American Dipper (Cinclus mexicanus), Harlequin Duck and Spotted Sandpiper (Actitis macularia). Harlequin Ducks had higher relative densities on the Elwha than the Hoh and Soleduck Rivers, but densities were similar to those found on the Duckabush River. There were greater numbers of Harlequin Ducks per linear kilometer above the two dams than between or below them. Relative densities of American Dippers on the Elwha were lower than on the Duckabush but not statistically different from those on the Hoh and Soleduck Rivers. Spotted Sandpipers had similar densities on all rivers except the Soleduck River where their numbers were lower. The piscivorous foraging guild was represented by the Common Merganser (Mergus merganser) and Belted Kingfisher (Ceryle alcyon). Common Mergansers were relatively more abundant on the Elwha River than on the other rivers due to their high numbers below the lowest dam where wild and hatchery anadromous fish are present. Belted Kingfisher relative densities showed no significant differences between rivers as they were found in low numbers on all rivers. Using relative abundances of some river dependent bird species as indicators of ecosystem recovery after dam removal may be useful tool surveys are continued throughout the process. In spite of lack of anadromy, the Elwha River ecosystem supports a significant population of Harlequin Ducks when compared to other Olympic rivers. American Dippers are also well represented on the Elwha River, specifically above the dams. Because of their relative abundance, these benthivore populations may have a measurable, upriver response to any nutrient enrichment as a result of dam removal and both species should be monitored. The Duckabush River, with a similar Harlequin Duck relative abundance in the lower reaches, should be monitored concurrently to account for region-wide population shifts of that species over time. The Common Merganser may be the best indicator of below dam effects on the Elwha River and numbers could be compared with the lower Soleduck River, however alternative survey methods, specifically drift boat surveys, should be considered to improve count accuracy. During June and July of 1997, time-activity budget data were gathered on NB/FB Harlequin Ducks on the Elwha, Duckabush and Dosewallips Rivers and at their mouths and at the mouth of Salt Creek. Time spent foraging by NBIFB Harlequin Ducks was similar among the three rivers examined. NB/FB Harlequin Ducks on the spent 33.1%, 33.2%, 36.4% of their time feeding, on the Elwha, Duckabush Dosewallips Rivers respectively. The Elwha River system was the only system where time activity budgets could be compared between river and adjacent coastal habitats. Time spent foraging at the mouth of the Elwha was significantly higher (52.5%) than on the Elwha River proper. Food availability on river habitat may be a factor in NB/FB females' decision to remain on river habitat during the breeding season or migrate to the ocean. Time-activity budgets provide information on Harlequin Duck life history but a better understanding of their foraging behavior and the role of food availability in habitat selection is needed before time-activity budgets alone can be used as a tool for assessing ecosystem response to dam removal. Time-activity budget data collected concurrently with food availability data from field studies, along with energetics and food preference data from field or laboratory studies may establish a clearer link between time spent feeding and habitat quality and preferences.
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