Rules#
Compete to see how many bird species you can identify during any consecutive 24-hour period within the event dates.
“Identifying a species” means visually confirming it or hearing its vocalization in a way that allows certain species identification.
Target species follow the Check-list of Japanese Birds, 8th Edition.
Participation is open to both individuals and teams.
For team participation, only species confirmed by all team members are counted.
Records are based on self-reporting, with honesty and integrity expected.
Important: Only one result submission is allowed per observation. Multiple observations or resubmissions during the event period are not permitted.
Eligibility#
Participants should have some birdwatching experience and be able to identify bird species.
Participants should be able to critically assess their own identification skills.
Recorded data will be made available for publication on GBIF (Global Biodiversity Information Facility) or Zenodo under your nickname or team name, and we aim to publish them on these platforms.
Please participate with honesty over winning, and creating a lasting record in mind. Importantly, it’s no fun unless you’re strict with yourself when creating your list.
Rankings#
🏆 The Big Day (BD)#
The main division of Big Day, competing to see how many species can be observed in a consecutive 24-hour period.
🏅 Only One (OO)#
A division that evaluates the number of species confirmed only by your team. Let’s all work together to challenge “How many species can be confirmed in Japan right now”!
Achievements (Challenge Categories)#
Starting in 2026, observations under specific conditions are evaluated as “Achievements.”
Important mechanism:
- Decide your achievement(s) before participating
- Your submitted list should consist only of species that meet the conditions of that achievement
- If one observation meets multiple achievement conditions, you can declare multiple achievements
Example: If you observe in your backyard for a consecutive 60 minutes at night
→ Applies simultaneously to Big Day (BD), Big Hour (BH), Big Sit (BS), Edge of Darkness (EoD), and Low Fossil (LF)
⏱ The Big Hour (BH)#
Compete to see how many species can be observed in a consecutive 60-minute period.
Conditions:
- Any consecutive 60 minutes during the event period
- One attempt only
🪑 The Big Sit (BS)#
Observe without moving from one location. Big Sit is an internationally established observation style.
Conditions:
- Remain at the same location (guideline: within a 100m radius)
- Observation duration is flexible (can be 1 hour or 24 hours)
- Brief departures for restrooms, etc. are allowed
🌙 Edge of the Darkness (EoD)#
A division targeting only completely dark hours.
Conditions:
- Records only from complete nighttime: after the end of civil twilight to before the start of civil twilight
⚠ Minimize disturbance to birds during observations and prioritize safety.
⛄ Whiteout (WO)#
Winter northern regions only. Test yourself in the frozen northern lands. *WO is exclusive to the New Year Big Day
Conditions:
- 70% or more of the land area within a 500m radius of the observation point must be covered with snow or ice
- Birds in open water or melted areas within the same environment are acceptable
🌊 Beyond the Horizon (BtH)#
A division targeting only birds confirmed in marine environments. Includes individuals on the sea surface, in the sea, or flying over the sea; estuaries and tidal flats are excluded.
Conditions:
- Only individuals on sea surface, in the sea, or flying over the sea
- Individuals on land, seawalls, or tetrapods are not allowed
- Birds resting on boats are acceptable
- Estuaries and tidal flats are excluded
🏔️ Vertical Limit (VL)#
A division challenging observations in high-altitude environments.
Conditions:
- Hokkaido and Tohoku 6 prefectures: 300m elevation or higher
- Kanto and westward: 700m elevation or higher *The above conditions are for the New Year Big Day
⚠ Mountainous areas in winter can be dangerous. Always stay within safely accessible areas.
🚶 Low Fossil (LF)#
A division where you travel only by foot, bicycle, or public transportation (trains, subways, buses). Minimize dependence on fossil fuels. Accessible even without a driver’s license or personal vehicle.
Conditions:
- Travel only by foot, bicycle, or public transportation (trains, subways, buses)
- Private cars (including electric vehicles), ferries, and airplanes are not allowed
How to Participate#
Please check the announcement for each event.
Schedule#
Currently held annually during New Year and Golden Week. Latest event schedules are announced on social media.
Social Media#
X (formerly Twitter) https://x.com/bigdayjapa43921
Facebook https://www.facebook.com/profile.php?id=61574800576073