Photographer Olga Ivashchenko joined forestry workers helping Ukraine's wild bison survive through the harsh winters of the Carpathian Mountains.
These are some of the wild bison that roam Ukraine's Carpathian Mountains, near the borders with Poland and Slovakia.
The bison are probably the descendants of animals brought to the area from Germany in 2009. European Bison were hunted to the edge of extinction a century ago, but have since made a steady comeback across the continent and in January they were removed from the list of Europe's "vulnerable" animals.
The photos were taken by Ukrainian Olga Ivashchenko in February, when she joined a group who help the bison of the Carpathians survive Ukraine's snow-clogged winters.
Ivashchenko rode with Vasyl Herych (pictured) and several other workers from Ukraine's Skole Beskids National Park as they trucked food up to the mountain-roaming bison.
During the snowy months, when the foraging bison struggle to uncover enough to eat, these men haul supplies to the animals.
The men deliver hundreds of kilograms of beets, hay, and cabbage to an isolated spot that only four-wheel-drive trucks are able to reach.
The bisons' food delivery is paid for by the Lviv regional government, as well as by donors that include the Frankfurt Zoological Society and the cosmetics company Lush. Without such help the animals would be more likely to wander down from the mountains in search of food and into contact with people.
European bison can eat up to 32 kilograms of food in a day. The animals find water themselves in winter, often by cracking through ice with their hooves.
The practice of people delivering food to wild bison through winters dates back several centuries, when bison were more common in the forests of Eastern Europe and some were under the protection of Europe's royal families.
While Ivashchenko was with the men laying out food for the bison, a herd of the animals appeared out of the forest to watch their human benefactors -- something the team told her happens rarely.
Ivashchenko told RFE/RL the foresters spotted the bison herd in the forest while driving. Herych then turned off the engine and the team quietly hopped out onto the snow.
A group of about 10 bison then watched the photographer as she cautiously approached the animals. "At that moment I felt vulnerable," Ivashchenko says. "After all, I'm on their territory and they may not like it." A European bison can weigh up to 1,000 kilograms.
The photographer says the only sound the animals made was the rustle of their hooves as they moved through the snow.
The population of European bison on the continent has increased from around 1,800 in 2003 to over 6,200 today. In Ukraine the population is slowly increasing and stands at about 350.
Ivashchenko says the small growth in numbers of Ukraine's wild bison is largely "thanks to the people who look after them" in the country's national parks.