Response of cavity-nesting birds to aquatic macroinvertebrate availability in the Cache River watershed, southern Illinois

Author

Douglas Richard McClain, Southern Illinois University CarbondaleFollow

Date of Award

5-1-2016

Degree Name

Master of Science

Department

Zoology

First Advisor

Eichholz, Michael

Abstract

Macroinvertebrates are an essential component of aquatic food webs, with some taxa having an influence on terrestrial environments as well. Because macroinvertebrates are often the link among trophic levels in aquatic systems, they can be affected by abiotic components in the environment and can subsequently affect higher trophic levels that depend on invertebrates as a food source. I examined the influence of aquatic macroinvertebrates in the Cache River watershed on the nesting distribution and clutch sizes of wood ducks, Aix sponsa, and Carolina wrens, Thryothorus ludovicianus. I sampled aquatic macroinvertebrates with two sampling methods to examine both their density and diversity. Furthermore, I installed and checked artificial nest boxes for wood duck and Carolina wren nests, taking their location and clutch size into account, to determine if either metric was influenced by food availability. Aquatic macroinvertebrate density was significantly different by wetland site, with the Lower Cache River Access having lower densities than the other sites. For both taxa richness and Shannon diversity, there was a significant interaction between site and sampling method, but neither main effect was significant. Both main effects (site and method) were significant for Shannon evenness, but the interaction was not significant. Furthermore, Naucoridae, Oligochaeta, Pleidae, and Copepoda were the taxa that most characterized the invertebrate communities and accounted for much of the dissimilarity among the communities as well. I found no evidence that nest density or clutch size varied among sites, for either wood ducks or Carolina wrens, even though macroinvertebrate biomass was significantly lower in the Lower Cache River Access site. A number of factors may explain why I did not observe the predicted variation, including, 1) birds were obtaining nutrients outside of the study area, 2) differences in invertebrate biomass were not adequate to produce a change in bird behavior, or 3) predator abundance was used as a more influential cue in nest site selection.