Estimating the effects of detection heterogeneity and overdispersion on trends estimated from avian point counts

Point counts are a common method for sampling avian distribution and abundance. Although methods for estimating detection probabilities are available, many analyses use raw counts and do not correct for detectability. We use a removal model of detection within an N-mixture approach to estimate abundance trends corrected for imperfect detection. We compare the corrected trend estimates to those estimated from raw counts for 16 species using 15 years of monitoring data on three national forests in the western Great Lakes, USA. We also tested the effects of overdispersion by modeling both counts and removal mixtures under three statistical distributions: Poisson, zero-inflated Poisson, and negative binomial. For most species, the removal model produced estimates of detection probability that conformed to expectations. For many species, but not all, estimates of trends were similar regardless of statistical distribution or method of analysis. Within a given combination of likelihood (counts vs. mixtures) and statistical distribution, trends usually differed by both stand type and national forest, with species showing declines in some stand types and increases in others. For three species, Brown Creeper, Yellow-rumped Warbler, and Black-throated Green Warbler, temporal patterns in detectability resulted in substantial differences in estimated trends under the removal mixtures compared to the analysis of raw counts. Overall, we found that the zero-inflated Poisson was the best distribution for our data, although the Poisson or negative binomial performed better for a few species. The similarity in estimated trends that we observed among counts and removal mixtures was probably a result of both experimental design and sampling effort. First, the study was originally designed to avoid confounding observer effects with habitats or time. Second, our time series is relatively long and our sample sizes within years are large

Standardized Measures of Coastal Wetland Condition: Implementation at a Laurentian Great Lakes Basin-Wide Scale

Since European settlement, over 50 % of coastal wetlands have been lost in the Laurentian Great Lakes basin, causing growing concern and increased monitoring by government agencies. For over a decade, monitoring efforts have focused on the development of regional and organism-specific measures. To facilitate collaboration and information sharing between public, private, and government agencies throughout the Great Lakes basin, we developed standardized methods and indicators used for assessing wetland condition. Using an ecosystem approach and a stratified random site selection process, birds, anurans, fish, macroinvertebrates, vegetation, and physico-chemical conditions were sampled in coastal wetlands of all five Great Lakes including sites from the United States and Canada. Our primary objective was to implement a standardized basin-wide coastal wetland monitoring program that would be a powerful tool to inform decision-makers on coastal wetland conservation and restoration priorities throughout the Great Lakes basin

Standardized Measures of Coastal Wetland Condition: Implementation at a Laurentian Great Lakes Basin-Wide Scale

Since European settlement, over 50 % of coastal wetlands have been lost in the Laurentian Great Lakes basin, causing growing concern and increased monitoring by government agencies. For over a decade, monitoring efforts have focused on the development of regional and organism-specific measures. To facilitate collaboration and information sharing between public, private, and government agencies throughout the Great Lakes basin, we developed standardized methods and indicators used for assessing wetland condition. Using an ecosystem approach and a stratified random site selection process, birds, anurans, fish, macroinvertebrates, vegetation, and physico-chemical conditions were sampled in coastal wetlands of all five Great Lakes including sites from the United States and Canada. Our primary objective was to implement a standardized basin-wide coastal wetland monitoring program that would be a powerful tool to inform decision-makers on coastal wetland conservation and restoration priorities throughout the Great Lakes basin

Physical and plant community changes at a Lake Michigan coastal marsh related to a two-meter increase in lake level

Located in Oconto County, Wisconsin, Oconto Marsh #2 is a Great Lakes Coastal Wetland Monitoring Program study site that borders the shoreline of Lake Michigan. Plant communities were characterized at Oconto Marsh #2 along three transects in 2011, 2016, 2017 and 2021, a period when Lake Michigan water levels increased by two meters. Transects were placed to intersect with three vegetation zones: submergent, emergent, and wet meadow. Here, we report on physical landscape changes and the vegetation composition changes that occurred from 2011 to 2021. From satellite imagery interpretation, we show approximately 61,000 m2 of what was emergent and wet meadow vegetation in 2011, transitioned into a submerged aquatic community in 2021. High energy wave action penetrating farther landward, a consequence of higher water levels, is likely most responsible for causing these changes. Plant species richness was lowest in 2011 (32 species) and ranged from 52 to 56 taxa in later years. Using multivariate ordination and PERMANOVA, we show plant composition in 2011 was different from 2016, 2017, and 2021. While invasive Phragmites australis was treated with herbicide in 2014, disturbance from progressively increasing water levels has facilitated considerable changes in plant composition and wetland zone extents since monitoring began. Despite successful treatment of P. australis, encounters with more non-native species while sampling farther landward in later years has caused site-wide declines in multiple metrics of floristic quality. Of critical importance, in 2021, we discovered invasive Hydrocharis morus-ranae at the site, the first documentation in the state of Wisconsin

Natural Resources Research Institute Technical Report

The breeding bird communities of the western Great Lakes region have among the richest diversity of breeding bird species in North America (Robbins et al. 1987; Green 1995, Rich et al. 2004). The importance of this diversity and concerns with potential declines of some species has led to a strong interest in monitoring forest bird populations in the region. The relatively heavily forested landscapes of northern Minnesota and Wisconsin are considered to be population 'sources' for many forest bird species and may be supplementing population 'sinks' in the agricultural landscapes of the lower Midwest (Robinson et al. 1995, Temple and Flaspohler 1998). Analysis of population trends is used as an 'early-warning system' of potential problems in a species population and serves as a measure of the ecological condition of the environment (Niemi and McDonald 2004). Large-scale population monitoring programs such as the U.S. Geological Survey’s Breeding Bird Survey (BBS) provide important information on trends at a continental scale. However, limited coverage in some areas can make it difficult to use BBS data to characterize population trends at smaller geographic scales (Peterjohn et al. 1995). Continental trends also have the potential to mask regional population trends (Holmes and Sherry 1988), thus there is a need for regional monitoring programs that can provide more localized information (Howe et al. 1997). In response to the need for regional population data, a long-term forest breeding bird monitoring program was established in 1991 in the Chippewa and Superior NFs, and in 1992 in the Chequamegon NF. The Forest Service is mandated to monitor certain management indicator species (Manley 1993), and our monitoring program expands beyond indicator species to include all forest songbird species that we can adequately sample. Currently, approximately 420 stands (1,271 points) within the three national forests are surveyed during the breeding season (June 1 to July 10). The primary objective of this report is to update U.S. Forest Service personnel on results of the forest bird monitoring program. Here we focus on relative abundance trends of individual species. Because we slightly changed our point count methodology in 1995 by including unlimited point counts, here we focus on a comparison of the results from three different distance radii x time categories: 1) 100 m radius distance for 1991-2009, 2) 100 m radius distance for 1995-2009, and 3) unlimited distance for 1995-2009. Our intent here is to summarize the most important results and to provide detailed information in appendix form for those who need more specific results