AUTHORS: Michael Wellik, US Geological Survey; Eileen Kirsch, US Geological Survey; Ryan Burner, US Geological Survey
ABSTRACT: Forested floodplains along the upper Mississippi River are important for breeding birds but are shaped by human use of the surrounding lands and especially by the construction of the lock and dam system in the 1940’s to control water levels. These forests are continuing to change because of higher water levels, maturing forests, and invasive species. We looked at potential changes in the avian community in forests by comparing bird species richness and species’ relative abundance and frequency of occurrence between data collected from 1994-1997 and 2015-2019. Point counts were conducted in three stretches of river at sites where there has been no direct forest management since the 1940’s. The same sites were sampled in several years during both time periods, using point counts with the same spatial scale and duration. The sites in the 1990’s were sampled once per year by a single observer, whereas in the 2010’s they were sampled multiple times by multiple observers each year. To account for this difference in yearly sampling effort we bootstrapped the 2010’s data, creating a distribution to compare to the yearly one-survey one-observer method used in the 1990’s. In this timeframe there was a slight decline in species richness for each of the three river stretches. Across all three stretches some species have declined in frequency of occurrence, such as the American Redstart, whereas others increased, like the Prothonotary Warbler. Examining bird community trends over decades, even with slightly different sampling methods, may benefit avian and habitat management.
