Trends in populations of breeding birds and habitat conditions in riparian areas along the Madison and Missouri Rivers, Montana 2004-2017

EXECUTIVE SUMMARY

Long-term assessments of the distribution and abundance of populations are central to evaluating the potential effects of human activities on wildlife. Since 2004, the University of Montana (UM), with funding from Northwestern Energy (formerly PPL Montana) and the Bureau of Land Management (BLM), has monitored bird populations and riparian vegetation on over 500 miles of the Madison and Missouri Rivers. This program meets Northwestern Energy’s Federal Energy Regulatory Commission (FERC) license requirements for hydroelectric operations on the river system by:

1. Monitoring main stem bird distributions and population trends as an indicator of wildlife habitat conditions,
2. Identifying critical wildlife habitats based on analysis of bird habitat use, and
3. Measuring bird and vegetative responses to management actions to evaluate project benefits for wildlife.

This report summarizes analyses of bird population and vegetation trends across five annual surveys between 2004 and 2017, and documents conditions at important management areas within the Upper Missouri Breaks National Monument since 2015. To date, our monitoring efforts have resulted in 1,638 point-count surveys and detection of 30,094 individual birds of 127 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 155, which represents 58% of species known to breed in Montana. The majority of species we observed were associated with riparian or wetland environments, including 24 Montana Species of Concern (MTSOC) and 29 U.S. Fish and Wildlife Birds of Management Concern. For 38 of those bird species, sample sizes were sufficient to generate precise annual estimates of density with the use of distance sampling methods.

Highlights of our findings include:
*Declining trends for many riparian obligate and dependent bird species, especially on the Madison River.
*Increasing densities of the Yellow-breasted Chat, a riparian obligate primarily found in the UMRB.
*No evidence that overall riparian species richness has changed.
*No Black-billed Cuckoos found in 2017, down from 5 occupied sites on UMRB in 2015.
*Significant differences in riparian species densities across ownership and management designation in the UMRB.
*Declining shrub and willow (Salix spp.) cover, especially on the Madison.
*Declining large cottonwood (Populus spp.) tree and snag density system-wide, but increasing small cottonwood trees, especially on the Missouri River.
*Livestock grazing intensity continued to decline markedly system-wide.
*No evidence of system-wide change in non-native Russian Olive (Elaeagnus angustifolia), density or invasive weed cover.

We found statistically significant declines in densities of 13 bird species and increases in densities of five species across time. Patterns we observed largely correspond to long-term trends documented across the region based on the North American Breeding Bird Survey. Such similarities suggest the drivers of population declines along the river system are likely operating across large spatial scales. We measured significant changes in riparian vegetation conditions since 2004, which are likely influencing habitat suitability for bird populations. Those changes include aging cottonwood forests, declining shrub cover, and loss of snags. We also documented baseline conditions and located important breeding areas for riparian bird species, including several bird species of concern, in the Upper Missouri River Breaks National Monument (UMRB).

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. However, these results should still be viewed cautiously, since inferences are based on estimates from only five years since 2004. Future monitoring will build on this dataset, providing a more complete picture of the patterns and drivers of trends in wildlife populations.