Funding for this project was provided by the Minnesota Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources (LCCMR).
The Trust Fund is a permanent fund constitutionally established by the citizens of Minnesota to assist in the protection, conservation, preservation, and enhancement of the state’s air, water, land, fish, wildlife, and other natural resources.
The rate at which climate is changing in northern latitudes presents a significant threat to bird populations that rely on boreal forests. Alterations in the distributions of trees and other plants as a result of warming will alter the habitat suitability of vast regions of boreal and hemiboreal forests. Climate change associated habitat alterations along with range expansions of bird species are likely to have substantial consequences on avian communities and biodiversity. Identifying factors that contribute to species coexistence and community assembly processes at local and regional scales will facilitate predictions about the impact of climate change on avian communities in these forest ecosystems. This paper provides a comprehensive review of historic and current theories of community ecology dynamics providing a theoretical synthesis that links the evolution of species traits at the individual level, the dynamics of species interactions, and the overall maintenance of biodiversity. Integration of these perspectives is necessary to provide the scientific means to face growing environmental challenges in boreal ecosystems.
Abstract Black ash wetlands cover approximately 1.2 million ha of wetland forest in the western Great Lakes region, providing critical habitat for wildlife. The future of these wetlands is critically threatened by a variety of factors, including emerald ash borer ( Agrilus planipennis ; emerald ash borer [EAB]), which has been eliminating native populations of otherwise healthy ash throughout the Great Lakes region since it was discovered in 2002. To quantify the potential impacts of tree mortality from EAB on wildlife communities, we measured seasonal bird, mammal, and amphibian diversity in black ash wetlands using a dual approach: (1) documenting bird and amphibian species across 27 mature reference black ash wetlands in northern Minnesota, USA and (2) assessing how bird, mammal, and amphibian communities respond to experimental manipulations of black ash forests that emulate mortality and management strategies related to the potential impact of EAB. In total, 85 wildlife species were recorded for the entire study including 57 bird species, 5 amphibian species, and 23 mammal species. Results from the reference sites show that hydrologic regime, percentage of ash canopy cover, and understory cover were important habitat characteristics for bird and amphibian communities. Results from the experimental sites show there may be short‐term increases in species richness for mammal and bird communities associated with changes in forest structure due to ash mortality; however, anticipated changes resulting from EAB‐caused mortality, particularly the conversion of these sites to non‐forested wetlands, will lead to significant shifts in bird and mammal community composition. Loss of ash may cause declines in forest‐dependent species and increases in open‐canopy and wetland‐associated species. Additionally, whereas increased ponding extent and longer hydroperiods may be beneficial for some amphibian species, the loss of the forest canopy will result in an overall decrease in bird diversity and reduce forest connectivity for all species. Our results indicate the potential for significant large‐scale impacts of black ash mortality on forest‐associated wildlife. Management strategies that focus on establishing alternative trees species to maintain long‐term forest cover and structural complexity in these wetlands will help to maintain and conserve wildlife diversity.
The Canada Warbler (Cardellina canadensis) is a species of high conservation importance because of its low overall density and long-term widespread population declines on the breeding grounds. Results of previous research on the species suggest that its breeding habitat preferences vary across its range. However, the underlying processes associated with habitat use are unknown. Using a 20 yr dataset, we developed occupancy models for Canada Warblers to determine the influence of habitat characteristics (e.g., understory vegetation, canopy cover), landscape context (e.g., edge, forest patch size), and species co-occurrence on occupancy, colonization, and local extinction parameters. Our results show that multiple habitats are used by Canada Warblers on the breeding grounds; common variables associated with large-scale, long-term occupancy dynamics are forest age, landscape composition at the 100 m and 500 m scales, and mean patch size. Overall, Canada Warblers were nearly twice as persistent in mature forest stands (>80 yr) and large, mixed forest stands. Further, models indicated that species co-occurrence was an important predictor of Canada Warbler occupancy in some cover types. The results of this study increase our understanding of population processes over large, dynamic landscapes and provide essential conservation information to improve habitat and landscape management for the Canada Warbler.
Effective conservation planning for species of concern requires long-term monitoring data that can accurately estimate population trends. Supplemental or alternative methods for estimating population trends are necessary for species that are poorly sampled by traditional breeding bird survey methods. Counts of migrating birds are commonly used to assess raptor population trends and could be useful for additional taxa that migrate diurnally and are difficult to monitor during the breeding season. In North America, the Common Nighthawk (Chordeiles minor) is challenging to detect during comprehensive dawn surveys like the North American Breeding Bird Survey and is considered a species of conservation concern because of steep population declines across its range. We conducted standardized evening counts of migrating Common Nighthawks at a fixed survey location along western Lake Superior each autumn from 2008 to 2022. To document peak migration activity, counts spanned ~3 hours each evening from mid-August to early September for a mean of 19.4 ± 2.4 days. These count data were then used to assess the effects of weather on daily counts and high-count days and to calculate population trends over this 15-year period. We used generalized linear mixed effects models to determine the relationship between daily counts and high-count days (i.e., ≥1000 migrating nighthawks) and weather variables. Additionally, using our 15-year dataset, we calculated a geometric mean passage rate that accounted for annual differences in weather to estimate count trends. Annual counts averaged ~18,000 (min = 2514, max = 32,837) individuals and high-count days occurred 56 times throughout the course of the study. Model results indicated lighter, westerly winds and warmer temperatures were associated with higher daily counts and greater probability of a large migratory flight. Results from the trend analyses suggest stable or non-significantly increasing trends for Common Nighthawks during this monitoring period; however, the trend models explained a relatively low percentage of the variation in the counts. Results from a power analysis suggest that continued monitoring efforts and adjustments with weather covariates will be necessary to effectively use visible migration count data to estimate Common Nighthawk trends. Establishing annual monitoring programs that use standardized visual counts to document Common Nighthawk migration at key sites across North America may provide supplemental information useful for population trend estimates of this species. Therefore, we advocate for the use of visible migration counts to monitor Common Nighthawks in North America and emphasize the value of long-term monitoring efforts.
