Jennifer Timmer, Bird Conservancy of the Rockies
Every year, biologists and technicians hike across the prairies and forests from the Great Plains to the Intermountain West to conduct breeding bird surveys for the Integrated Monitoring in Bird Conservation Regions (IMBCR) program. The IMBCR program was created in 2008 in response to bird population declines and national recommendations for improving bird monitoring. Today, the IMBCR program is the second largest breeding bird monitoring program in North America, spanning 16 western states (Fig. 1). The strength of the IMBCR program lies in its partnership with multiple state and federal agencies and nonprofit organizations. Bird Conservancy of the Rockies leads the effort while several organizations help collect the data. Monitoring resources are pooled among the partners in a spatially balanced, probabilistic framework, which promotes a more efficient use of resources and allows us to monitor larger spatial and temporal extents compared to individual monitoring efforts. It also allows us to estimate population sizes with certainty to better inform management and conservation decisions.
The IMBCR sampling design starts with the intersection of Bird Conservation Regions (BCR) and state boundaries and is then stratified or divided up based on areas to which partners need information about birds, such as an individual field office or national grassland. Stratification is based on boundaries and other attributes that are unlikely to change over time as opposed to stratification based on vegetation types. Beginning each spring, technicians and biologists visit over 2,000 1-km2 transects across the IMBCR footprint. Some transects are located miles from nearby roads, while others are in city limits. They record all birds seen and heard during a six-minute survey at up to 16 point count stations in a transect. They also estimate distance to each bird and record the minute interval a bird was detected. These two pieces of information allow us to account for birds present at a survey location but not detected (i.e., detection probability). Once the data are collected, many hours are spent entering data and conducting quality control checks. After data collection, entry, and proofing, Bird Conservancy biometricians analyze all of the detections. Population estimates (e.g., density, abundance, occupancy, and population trend) are then available at multiple spatial scales for more than 270 different landbirds, including songbirds, gamebirds, and common waterfowl and raptors.
The Bureau of Land Management (BLM) has been an IMBCR partner since the program began in Colorado, and was instrumental in the recent IMBCR expansion into Oregon and California to provide near-complete coverage of the sagebrush ecosystem and its imperiled birds. The sampling design allows BLM biologists to compare population estimates for a field office to estimates across all BLM lands in a state or state-wide and BCR-wide for context. Vegetation data, such as shrub and ground cover, are also collected at the start of every point count survey, so that we can relate bird populations to vegetation changes from management actions or natural disturbances.
Population estimates, species counts, and sampling effort for the various IMBCR strata, or areas of inference, are housed on the Rocky Mountain Avian Data Center (RMADC), a node of the Avian Knowledge Network. To access information from the RMADC, users need to select one or more filters, such as “species”, “year”, or “individual stratum” to narrow their query of the large database. Once the query has run, users can view estimates, such as density (number of birds per square kilometer) and occupancy (probability a sampling unit is occupied) with estimates of precision, like the coefficient of variation. Follow this link and click the red “Run Query” button (Fig. 2) to view density and occupancy estimates for Brewer’s Sparrows in the Rock Springs Field Office in southwestern Wyoming. Short videos explaining how to query information from the RMADC and interpret the population estimates can be found here.
BLM biologists use occurrence data and population estimates to update Resource Management Plans (RMP), which serve as a guide for management of land and resources with multiple uses. Along with the RMPs, biologists also conduct environmental assessments to understand potential project impacts on migratory birds and place these impacts in context to surrounding populations. Is a project going to impact a denser population of Brewer’s Sparrow relative to the surrounding region? Biologists can even estimate potential population impacts from a project by multiplying the density of individuals across a Field Office by the project area (although these impacts also depend on proximity to other disturbances, the timing and duration of the project, etc.). If a project is only going to impact one or few vegetation types, such as sagebrush shrublands, estimates can be post-stratified by vegetation type within a field office to better understand project impacts on birds. For example, how many Pinyon Jays could be impacted by a pinyon-juniper removal project in a Utah Field Office? Along with the population estimates, IMBCR partners have access to the raw data they fund or collect (i.e., bird detections, survey locations, and vegetation data), while IMBCR data are available to those outside of the IMBCR Partnership upon request and approval of a data sharing agreement.
In addition to the baseline monitoring program, IMBCR partners also design targeted projects (i.e., overlays) to ask specific management questions or evaluate conservation efforts. They use the same IMBCR field methods and sample selection, but monitoring is conducted within specific project areas. This allows us to use detection data from across the IMBCR program to estimate population size for infrequently detected species in project areas and place them in regional context. For example, migratory birds were monitored inside the Atlantic Rim Natural Gas Development Area in south-central Wyoming to determine the impact on sagebrush-obligate species (Fig. 3). For this adaptive management project, BLM biologists set management triggers for the species by comparing occupancy estimates inside the project area to estimates on surrounding BLM land; if occupancy estimates for the species of concern declined at a greater rate inside the project area relative to surrounding BLM lands, natural gas activities would be suspended or biologists would implement mitigation measures. In another overlay project, BLM biologists in Idaho are interested in the response of sagebrush-obligates and other species, such as green-tailed towhees, to early phase juniper removal efforts meant to improve habitat for sage-grouse. Monitoring is occurring pre- and post-treatment to better understand the effects of juniper removal on the species of interest. In overlay projects, monitoring often occurs pre- and post-treatment to better inform future project impacts on migratory birds. In this way, biologists can extend the knowledge gained from one project to future projects and so extend limited monitoring resources.
Together, baseline monitoring through the IMBCR program and targeted overlay projects provide critical information about bird populations across private and public land in the western US. This information is needed now more than ever as recent studies document bird population declines across many species and guilds. We also need to work together to make management and conservation decisions that will impact bird populations because birds do not recognize state and other boundaries; indeed birds connect the world.