Trends in populations of breeding birds and habitat conditions in riparian areas along the Madison and Missouri Rivers, Montana 2004-2019

Long-term assessments of the distribution and abundance of populations are central to evaluating the potential effects of human activities on wildlife (Pollock et al. 2002). Since 2004, the University of Montana (UM) has monitored bird populations and riparian vegetation on over 500 miles of the Madison and Missouri Rivers on behalf of the Northwestern Energy Wildlife Technical Advisory Committee and the Bureau of Land Management (BLM). This program meets Northwestern Energy’s Federal Energy Regulatory Commission (FERC) license requirements and meets the purpose and intent of the Project 2188 Five Year (2018-2022) Wildlife Plan article 423 by:
1. Measuring main stem bird community and riparian vegetation change over time as an indicator of wildlife habitat conditions,
2. Identifying critical wildlife habitats based on analysis of bird habitat use in relation to vegetation measures, and
3. Providing feedback on techniques employed to protect, mitigate, and enhance native plants and wildlife populations within the main stem river system;

This report summarizes analyses of bird population and vegetation trends across six annual surveys events between 2004 and 2019, and provides recommendations for future efforts. To date, we have completed 1,867 point-count surveys, counted 32,091 individual birds, and documented 131 species during standardized point-count surveys. We also observed additional bird species outside the standardized survey period, bringing the total number of species observed to 159, which represents 60% of species known to breed in Montana. The majority of species we observed were associated with riparian or wetland environments, including 25 Montana Species of Concern (MTSOC) and 29 U.S. Fish and Wildlife Birds of Management Concern. Sample sizes were sufficient to generate precise annual estimates of density for 39 species with the use of distance sampling methods.

We found statistically significant declines in densities of 20 bird species (53% of species analyzed) and increases in densities of two species across time. Declining species have a broad range of nesting and foraging requirements, and include both generalists and riparian specialists. Patterns we observed largely correspond to long-term trends documented across the region based on the North American Breeding Bird Survey (BBS; Sauer 2018). Such similarities suggest the drivers of population declines along the river system are likely operating across large spatial scales. Significant changes in riparian habitat conditions since 2004, are likely influencing habitat suitability for bird populations. Those changes include aging cottonwood forests, declining shrub cover, and increases in some invasive species.

This program provides a direct measure of the status of wildlife within riparian areas across a large stretch of the Madison and Missouri Rivers, and is currently the only monitoring effort targeting riparian birds in Montana. Our findings are consistent with declines first observed in 2015, and encompass a 15 monitoring period. Nevertheless, findings are based on only six survey years. Future monitoring will build on this dataset, providing a more complete picture of changes in wildlife populations over time.