Date of Award
Master of Science
An in-stream restoration practice can have far-reaching ecological effects. A series of rock weirs was installed in the upper Cache River, Illinois, in 2001 and 2003 to stabilize the channel and control entrenchment. I examined responses of insect emergence production and riparian birds to these structures. I quantified insect emergence seasonally in 2009 and 2010 and made weekly point counts of birds during spring of both years at 4 weir and 4 non-weir sites. Emerging insect abundance was higher at non-weir sites (p = 0.005), but species richness (d) and diversity (H') were higher at weir sites (d, p < 0.001; H', p < 0.001). Total emergence production did not differ between site types, but larger-bodied taxa were more productive at weir sites. Non-metric multidimensional scaling (NMDS) ordinations revealed differences in assemblages at weirs and non-weirs. Chironomidae (Diptera) thrived in the ambient scoured clay streambed at non-weirs, explaining the difference in abundance and similarity in emergence production between weir and non-weir sites. However, abundance and emergence production of Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa were higher at weir sites (p < 0.001 and p = 0.009 respectively). Birds showed a positive numerical response to weirs. Total bird abundance was higher at weir sites (23.18 ha-1) compared to non-weirs (20.16 ha-1) and NMDS indicated differences in bird assemblages between site types. Analysis of similarity (ANOSIM) showed differences in bird (2009, p = 0.08; 2010, p = 0.11) and insect (abundance, p = 0.029; emergence production, p = 0.029) assemblages between site types. There was no difference in clutch size or feeding rates between sites, but the number of hatchlings and fledglings was higher at non-weirs. Cowbird (Molothrus ater) parasitism was higher at weir sites, most likely due to the decreased canopy cover present at weir sites as a result of the installation of the rock weirs. Weirs appear to be beneficial in that they harbor high densities of large-bodied insects and may represent feeding `hot spots' for insectivorous birds and likely other riparian insectivores such as bats and amphibians. However, the alterations to the riparian habitat associated with installation of weirs (creation of more edge habitat) may have a negative impact on birds through increased predation and cowbird parasitism. This study is the first to show avian responses to an in-stream restoration practice.
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