From the ebird website:
Mark your calendars for October Big Day—10 Oct 2026! Like Global Big Day, October Big Day is an opportunity to celebrate our shared love of birds. Last October, 900,000 people united for a single day of birding. Can we beat that number and make this year the first October Big Day with more than a million people enjoying birds together?

More details at: https://ebird.org/news/october-big-day-2026