The North American Breeding Bird Survey (BBS) is a large-scale bird population monitoring program that tracks trends and populations of hundreds of bird species across North America. It provides long-term data on bird abundance and distribution dating back to the 1960s.
Overview of the BBS
The BBS program was established in 1966 as a cooperative effort between the U.S. Fish and Wildlife Service and the Canadian Wildlife Service. It involves thousands of skilled volunteer birdwatchers who conduct annual surveys along pre-determined roadside routes during the height of the breeding season (June).
There are over 4,100 active survey routes across the continental U.S. and Canada, covering over 40,000 miles of roadways. Each route is 24.5 miles long with survey stops every 0.5 miles. At each stop, observers conduct 3-minute point counts, recording all birds seen or heard within a 0.25-mile radius.
The BBS aims to track the status and trends of North American bird populations. The data can reveal population increases or declines of species across their ranges. It allows scientists to estimate relative abundances of species and monitor changes over time.
Key Features of the BBS Dataset
The BBS dataset contains 50+ years of abundance data on over 420 bird species. Some key features include:
- Covers all states and provinces of the continental U.S. and Canada
- Contains over 6 million point count surveys conducted annually in June
- Tracks 420+ bird species, including both common and rare birds
- Provides annual indices of abundance for each species
- Allows analysis of population trends over time and across regions
- Data are collected using a standardized protocol for consistency
- Surveys are conducted by skilled volunteer birders
The BBS design randomizes roadside routes across the landscape to obtain representative coverage of bird populations. Routes remain constant over time so data reflects actual population changes rather than variations in coverage.
Types of Data Collected
The BBS collects three main types of data on bird populations:
- Occurrence – Presence or absence of each bird species on survey routes and stops
- Abundance – Number of birds recorded of each species at each survey stop
- Breeding evidence – Behaviors indicating breeding like carrying nest material, singing males, family groups
In addition, environmental data such as habitat type, weather conditions, and management activities are recorded. Time and date of surveys are also documented.
Applications of the BBS Dataset
The BBS dataset supports a wide array of conservation, research, and management applications including:
- Monitoring status of endangered/threatened species
- Identifying population declines to conserve at-risk birds
- Understanding bird distribution patterns and habitat associations
- Analyzing long-term population trends of species
- Assessing effectiveness of management programs and policies
- Modeling impacts of environmental change and land use
- Informing bird conservation planning across North America
Hundreds of peer-reviewed papers have used BBS data to study bird population dynamics, distributions, and responses to landscape changes and climate over time.
Accessing the BBS Dataset
The BBS dataset is freely available to the public online through the USGS Patuxent Wildlife Research Center at https://www.usgs.gov/centers/pwrc/science/north-american-breeding-bird-survey.
Data can be downloaded in CSV format with annual indices of relative abundance for each species. There are also interactive visualizations and summary reports. Supporting materials explain survey methodology, data limitations, and key definitions.
In addition, the Cornell Lab of Ornithology hosts a portal with convenient access to BBS data, maps, and graphs at https://www.birds.cornell.edu/home/getstarted#bbs.
Users must agree not to redistribute raw data but can freely share and publish results and graphs.
Data Collection Methods
BBS data are collected annually in June using standardized methods:
- Skilled volunteer birders conduct surveys along designated roadside routes.
- Each route is 24.5 miles long with stops at 0.5 mile intervals.
- At each stop, a 3-minute point count is conducted within a 0.25 mile radius.
- All birds seen or heard are recorded by species.
- Surveys start 30 minutes before local sunrise and take 4-5 hours.
- Data on weather, habitat, and breeding evidence are collected.
Survey routes are randomly located on secondary roads across the landscape. Routes remain constant between years to allow direct comparison of data.
Over 4,100 routes are surveyed across the continental U.S. and Canada. Routes are stratified by habitat type and physiographic regions.
Experienced observers conduct surveys using the same methodology each year. Many participants have surveyed their route for 10-20+ years.
Limitations
Despite standardized methods, the BBS dataset has some inherent limitations and biases:
- Only samples birds along roadsides in rural habitats
- Lacks coverage in urban areas, northern forests, and mountaintops
- Detectability varies by habitat, species, observer, weather, and time of day
- Trend accuracy declines for rare, cryptic, or nocturnal species
- Point counts may miss non-singing and non-vocal species
- Does not account for birds flying between stops
Experts analyze BBS data understanding these constraints. The data may under-represent certain species while overestimating common vocal birds.
Notable Trends and Insights
Analysis of long-term BBS data has revealed many notable trends and insights about bird populations. Some examples include:
- 33% of bird species declining, while 39% increasing over past 50 years
- Severe declines in grassland species due to habitat loss
- Increasing trends for wetland species like waterfowl
- Declining trends for aerial insectivores like swallows
- Range shifts northward for many eastern forest birds
- Declines linked to widespread threats like climate change and cat predation
By modeling BBS data over time, researchers gain critical insights into environmental impacts on bird populations. The dataset provides an early warning system for species in decline.
Data Analysis and Visualization
The BBS dataset allows various analytical approaches to understand bird population changes. Some examples include:
- Trend analysis – Assess species trends over time using statistical models
- Power analysis – Estimate power to detect trends based on sampling effort
- Species distribution modeling – Map habitat suitability using environmental data
- Richness estimators – Estimate species richness and detection probabilities
- Landscape analysis – Relate trends to land cover, climate and human factors
- Hierarchical modeling – Estimate effects of covariates like weather and habitat
BBS data can be integrated with weather, land cover, human footprint, and other environmental datasets to gain insights.
The USGS and Cornell Lab provide an online data visualization tool called the Bird Population Explorer. It generates interactive maps, graphs, and tables to explore BBS results.
Example graph showing population trend for a species:
Figure 1. Example BBS graph showing population trend for a sample species from 1966-2019.
Conclusion
In summary, the North American Breeding Bird Survey is an invaluable long-term dataset for monitoring bird populations across the continent. The BBS provides a rigorous sampling framework with 50+ years of abundance data on over 400 species of birds.
Despite some limitations, analysis of BBS data yields critical insights into bird population trends, distributions, and conservation needs. The program will continue generating data to guide bird management and research in the future.