A cow stands near to a group of bison last week near Wasilkowo, Poland. The cow escaped from its pen three months ago and has been roaming with a herd of bison. (Rafal Kowalczyk/AP)

A farmyard cow in Poland has chosen freedom this winter, roaming with a herd of bison for three months after escaping its pen.

The reddish brown cow has been spotted following bison across fields in eastern Poland as they forage for corn cobs and other food.

Rafal Kowalczyk, a bison expert who photographed the unusual sight, said the cow seems to be in good condition. That indicates that she is managing to find food, even though she is sometimes spotted on the margins of the herd. Thick fur common to her Limousin breed and the mild winter in eastern Poland so far this year have also helped her, he told the Associated Press on Thursday.

Kowalczyk, director of the Mammal Research Institute at the Polish Academy of Sciences, described the situation as exceptional, saying it's the first time he has witnessed a cow living among bison. But it's also dangerous to both sides.

If the cow mates with male bison and gets pregnant, she could die during delivery because her hybrid calf would be bigger than a normal cow calf.

Any offspring could also contaminate the gene pool of the tiny and endangered bison population in Poland, which became extinct in the wild after World War I and has been restored with the help of captive survivors.

For now, the story of a rebel cow who decided to roam free with the bison is a hit on Kowalczyk's Facebook page.

One of his followers reposted the photo with the words: "Next time when I think that something stops me from fulfilling my dreams, I will remember the cow who became a bison."

But scientists will want to remove the cow from the herd by summer to prevent the risk of mating, though Kowalczyk said that won't be an easy operation.

"One question is whether when winter ends the cow will follow the bison into the forest, which is not the habitat that this cow knows," Kowalczyk said. "The more time she spends in the herd, the riskier it will be."