In the early 1900s the bison were reintroduced - 7 females and 5 males, from Zoos in Europe including some from Queen Victoria. Some of the males were infertile, so there is a bit of inbreeding but the numbers have increased enough that they are no longer critical. The forest is now home to 800 European bison - Europe's heaviest land animal.
Took a guided tour with Met Arek Szymura, an ornithologist running Pygmy Tours. He started life as a musician, then coal miner and then he discovered birds. He moved to Bielowieza more than 29 yrs ago and has helped set up the National Park and improve its status. He was very enthusiastic and obviously knowledgable.
On day 2 took a cart ride (behind old horse) through the lanes to the Belarus border which is less than 10km away. Then we came home cross country through the forest tracks - 4X4 horsepower as the tracks were muddy and waterlogged from the rain the previous days. The driver spoke no English but kept pointing at things on the way and telling us long stories.
Misplaced the photos so may update when I find them.