Overview
Project Name
Christmas Bird Count
Access Level
By Request
Year started
1900
Year Ended
ongoing
Dataset
Christmas Bird Counts
About
Dataset summary
The data provided here are processed trends in relative abundance. Trends are available for over 500 species for a wide variety of spatial units from states and provinces to Bird Conservation Regions to nations. Trends are accompanied by the annual relative abundance indices that are used to generate the trends. These indices allow a user to calculate trends over a custom time period. Raw data from the Christmas Bird Count are available by request.
Season(s) and frequency
one day between December 14 through January 5 inclusively
Geographic area covered
Canada, United States, Mexico, Central America, South America, Caribbean Islands and Pacific Islands.
Primary species covered
All birds, but coverage probably best for landbirds and waterbirds (few counts of pelagic species)
Goals
The primary objective of the Christmas Bird Count is to monitor the status and distribution of bird populations across the Western Hemisphere. The count period, which is from December 14th to January 5th, in North America is referred to as "early winter," because many birds at this time are still in the late stages of their southward migration, so it is not "true" winter. When we combine these data with other surveys such as the Breeding Bird Survey, we begin to see a clearer picture of how the continent's bird populations have changed in time and space over the past hundred years. The information is also vital for conservation. For example, local trends in bird populations can indicate habitat fragmentation or signal an immediate environmental threat, such as groundwater contamination or poisoning from improper use of pesticides.
Methods
Sampling Design
Volunteers follow specified routes on foot, by car, bicycle, boat, snowmobile, and by observing feeders within a designated 15-mile (24-km) diameter circle. All birds seen or heard are counted from dawn to dusk on one day of the year between 14th December and 5th January. Optional nocturnal census conducted in some areas.
Field methods
Circular plot census
QA/QC
Although we attempt to minimize errors, a small percentage of CBC reports may be incorrect and analysts must be aware that misidentifications, data entry errors, and other sources of error can evade our data review process. All data pass through a review process that involves geographically specific experts. When these reviewers flag concerns, compilers are able to check and correct entries. Editorial flags used by regional reviewers are retained in the data set and should be consulted to determine if records should be included in a specific analysis.
Analysis methods
Summary results of CBCs published in American Birds (formerly Audubon Field Notes); main database available on the internet
Advice
As with any monitoring data, a recorded observation is a function of both the biological event (number of species actually present) and the observation process (probability that an individual bird, when present, will be observed, which is factor of the number of observers and/or the amount of time spent observing). We strongly suggest that analysts minimally include predictors of the observation process, namely, the effort expended by participants, as predictors in their statistical models, in order to describe increasing probabilities of observing birds with increasing time spent in making observations. For example, a commonly used effort method for standardizing counts is the party hour. Party hours are the number of hours that all parties spent in the field from dawn to dusk, not including nocturnal hours or feeder watching hours. Other metrics to consider are party size and distance covered by a variety of modalities. When analyzing CBC data, please carefully consider which effort measurements are most appropriate for your specific research questions and target species. The species names in this database follow the American Ornithological Union (AOU) nomenclature as it existed in the early 2010s. The species list in this database has not been updated to reflect any name changes or lumping and splitting of species that have taken place since that time and does not reflect current taxonomic classifications. Users should be aware of this when working with CBC count data.
Partners
National Audubon Society
Citation
National Audubon Society and Birds Canada. 2025. "Christmas Bird Counts". Data accessed from NatureCounts, Birds Canada. 10.71842/1psg-b417
