Skip to main content

Why is there an official CBC Count period and can we count outside of it?

Key points:

  • Official period: December 14 to January 5 (23 days). These dates remain the same each year.

  • No exceptions: counts conducted outside these dates are not accepted because they are not statistically comparable.

  • Historical context: these dates represent the boundaries (December 14 and January 5) used throughout the Christmas Bird Count database.

Scientific context: The period from December 14 to January 5 was established following the 100th Christmas Bird Count to resolve decades of confusion caused by a variable count period. This 23-day window encompasses the full range of dates used throughout the history of the Christmas Bird Count and cannot be extended. An independent scientific peer review concluded that any extension would compromise the statistical integrity of over a century of trend data, thereby undermining one of the most important existing bird population databases. Like the Breeding Bird Survey, the Christmas Bird Count serves as an essential reference tool for ornithologists and conservation biologists assessing the health of bird populations across the Americas. Maintaining this fixed period preserves the scientific value of the tens of thousands of volunteer hours contributed each season and ensures that the Christmas Bird Count remains a reliable resource for conservation science.

Did this answer your question?