This 6 July 2020 video from Yellowstone National Park in the USA says about itself:
How Bison Are Helping Cliff Swallows Build Their Nests
It’s a partnership that’s as unlikely as any: herds of bison on the move are kicking up chunks of earth. This, in turn, gives cliff swallows the valuable mud pellets they need to build their nests.
Dear Kitty. Some blog 