Carl
There is mention of the Spanish bison participation in the rewilding Europe website… Although it is from 2015….
Here: https://rewildingeurope.com/news/18-newborn-european-bison-in-the-european-rewilding-network-areas/
“Another member of ERN in Spain, Atapuerca, received one of the Dutch born bulls that met up with two females to start a new reproductive herd in an area where wild horses and cattle roam. The herd currently consists of 22 animals as two bulls were translocated to Spanish bison areas in early August.”