The Christmas Bird Count is an annual bird census organized by the National Audubon Society to track trends in bird populations. It began in 1900 and has become one of the longest-running wildlife census projects in the world. The count period refers to the timeframe during which the Christmas Bird Counts take place each year. The official count period is December 14th to January 5th. During these 3 weeks, volunteer birders across North America take part in local Christmas Bird Counts and submit their data to the National Audubon Society. Over 2,000 individual counts take place each year.
History of the Christmas Bird Count
The Christmas Bird Count began in 1900 as an alternative to a holiday tradition known as the Christmas “Side Hunt”. During Side Hunts, teams competed to see who could shoot the most birds and small mammals on Christmas Day. Conservationist Frank Chapman proposed counting birds instead of hunting them. The first Christmas Bird Count took place on December 25, 1900 with 27 observers conducting a census in 25 locations across North America.
By the 1930s, the Christmas Bird Count had become a well-established annual tradition. During World War II, many established count circles had to be abandoned but new ones were started up. In 1949, the Audubon Society took over management of the Christmas Bird Count. The count regained popularity in the 1950s and the number of circles continued to increase. The Christmas Bird Count embraced new technologies like telephones, tape recorders, binoculars, and field guides. Today, the Christmas Bird Count is one of the world’s largest and longest-running database on bird distribution.
Timing of the Christmas Bird Count
The timing of the Christmas Bird Count during the winter months provides important data on early winter bird populations. The counts take place during the coldest months when food is scarce. The census provides a snapshot of how birds are faring during the harshest conditions. Because the Christmas Bird Count has a long historical record, scientists can analyze population trends and how birds are responding to habitat changes and threats like climate change.
The count period is limited to a three-week window in December and early January to standardize the timing of the counts. Counts conducted in December when lakes are not frozen will yield different results than January counts when migration patterns shift. Limiting the window provides consistency for scientific analysis even though the timing may not always provide ideal counting conditions. The winter focus also avoids complications from variable migration patterns during spring and fall.
Start and End Dates
The official start date for the Christmas Bird Count period is December 14th. However, some count circles start earlier than the official date. Counts ending by January 5th will be accepted into the CBC database. Counts conducted after January 5th are considered late season counts and are not included in the official CBC data. This standardized period allows the data to be compiled for scientific analysis.
Duration
The Christmas Bird Count is conducted over a 24-hour period on one calendar day during the count period. Counts are usually done during daylight hours but some circles also collect data from owl prowls at night. Most counts take place on a date between December 14th and January 5th that is convenient for the local community. Rarely, a count may be postponed because of weather conditions like heavy snow or rain.
Christmas Bird Count Zones
The Christmas Bird Count is conducted within established census zones known as count circles. Each count circle is 15 miles in diameter creating a circle that covers about 177 square miles. This standardized area allows data to be compared across regions. Beginning in the 1950s, the circles were organized on maps to minimize overlap. Existing circles were given priority while new circles filled in gaps to achieve continental coverage. Today, over 2,400 count circles encompass all of North America.
When the count first began, the circles were centered on the locations ofAudubon society chapters that volunteered to conduct a count. Now, the circles are strategically located based on ideal birding locations. Coastal and urban areas tend to have higher densities of count circles because of higher bird populations. In remote areas, count circles may be spaced further apart due to smaller bird populations over large undeveloped landscapes.
Overlap
Ideally, the Christmas Bird Count circles do not overlap. However, some minor overlap may occur between adjacent circles. Overlapping counts are usually done on different days. In a few cases, overlapping circles will schedule their counts on the same day and divide the area between the circles. This minimizes duplicate counting and allows the areas to be covered in one day. Extensive coordination is required to allocate the zones and bring the results together while avoiding double counting.
Boundary Changes
The locations and boundaries of Christmas Bird Count circles are generally stable from year to year. However, circles can be retired or relocated if they become inactive. New circles may be created to fill gaps. Other circles may be relocated or resized to optimize coverage and birding habitat. Circles with a long continuous history are generally preserved to maintain the continuity of historical data even if conditions have changed.
Participating in the Christmas Bird Count
Anyone can participate in the Christmas Bird Count. Beginning birders are encouraged to join an established count circle to gain experience. The count compilers who organize the local counts are always eager to have more birders covering their circles. With over 2,400 circles, there are many opportunities to join counts across North America.
Join an Existing Circle
The easiest way to participate is to join an existing Christmas Bird Count in your area. Circles are listed on the Audubon Society website along with contact information for the compilers. You can reach out to the local compilers to join their count. Let them know your birding experience so they can assign you to an appropriate territory within the count circle.
Explore a New Area
You can also search for Christmas Bird Counts in an area you’ll be traveling to and join a count circle there. It’s a great way to connect with local birders and explore new territory. Historical results will give you an idea of what birds you might encounter. You may be able to provide valuable data from territories that are under-birded.
Start a New Circle
If there is not an existing Christmas Bird Count in your area, you can propose starting a new one. Contact your regional Audubon chapter or the National Audubon Society to get the process started. You’ll need to recruit volunteers to help cover the proposed territory. It may take a few years to build up a stable count circle.
Submitting Christmas Bird Count Data
After the count, participants report their results to the count compiler. The data is carefully reviewed, compiled, and submitted to Audubon through an online database or detailed report forms. Feeder watchers also contribute data on birds visiting their feeders within the count circle.
Reporting Format
Count compilers organize the data and submit a detailed report for every species observed. The report includes:
- The common name and scientific name for each species
- The total number of individuals counted for each species
- The number of birds counted within each party’s assigned territory
Unusual sightings must be well documented and verified by count compilers or regional editors.
Data Review
Regional editors review the count reports for accuracy, formatting, and unusual sightings. They ensure the data is complete and consistent before it enters the CBC database. With over 2,000 circles, this review is essential to maintaining data quality.
Research Access
The Christmas Bird Count database provides researchers and conservation groups with a treasure trove of information on bird populations. Scientists have used the long-term data to study the impacts of climate change, urbanization, declining habitats, and other threats to birds. The standardized methodology provides a consistent source of high quality data for detailed analysis.
Conclusion
For over a century, the Christmas Bird Count has mobilized volunteer birders to collect vital data on early winter bird populations across the Americas. The three-week period from December 14th to January 5th provides a standardized window that allows scientifically valid analysis of the extensive data. Birders are encouraged to join existing circles or start new ones to help fill gaps in coverage. The Christmas Bird Count remains one of the most important tools for understanding and protecting bird populations through citizen science.