Knutson 1995 abstract

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Knutson, M.G. 1995. Birds of large floodplain forests: Local and regional habitat associations on the upper Mississippi River. Ph.D. Dissertation, Iowa State University. Unpaged.

Abstract:

I studied local and regional habitat associations of birds breeding in floodplain forests of the Upper Mississippi River (UMR) during 1992-94. Floodplain forests provide breeding season habitat for at least 84 bird species, including floodplain forest specialists, cavity nesters, and some neotropical migrant birds that are experiencing regional population declines. Species richness overall and relative abundances of several groups of birds classified by management risk categories and guild associations declined in 1994. Lowered abundance and species richness in 1994 may have resulted from effects of the 1993 flood.

Overall, vegetation (small scale) factors had a larger influence on bird abundances than landscape matrix (large scale) factors. Bird species richness, and the abundance and richness of hole nesting and bark gleaning bird guilds, are associated with a landscape matrix dominated by mature forests. Many species, identified by others as area sensitive in uplands, do not show these patterns in the floodplain. If relative abundance is a reliable indicator of habitat quality, the UMR floodplain provides important habitat for some area sensitive species such as the American redstart (Setophaga ruticilla), blue gray gnatcatcher (Polioptila caerulea), yellow throated vireo (Vireo flavifrons) and yellow billed cuckoo (Coccyzus americanus).

In an artificial nest study, I found large forest tracts had higher nest predation rates than small forest tracts (52.3% vs. 36.3%) and predation rates decreased over the nesting season. There was no significant difference in predation rates among nests placed 25, 50, 100 or 200 m from the forest edge. Calculated artificial nest "survival" derived from observed predation rates in 1993 - 94 were comparable with natural nest survival estimates from the same study area in 1992. Vegetation variables measured at the nest site did not differ between intact and depredated nests.

Since we have only begun to study the role of floodplain forests as wildlife habitats on the UMR, the most prudent management recommendation is to conserve the existing forests in as close to their present state as possible, with no additional loss of forest. Restoration of higher elevation terrace forests would increase tree species diversity and provide additional habitat for birds.

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