Black-billed magpies (Pica hudsonia) are known for picking ticks from the backs of large mammals such as deer, elk, moose and livestock. The magpie either eats the ticks or caches the excess for later use. Unfortunately, most of the cached ticks are still alive so can go on to reproduce, rather than become a magpie meal.
I noticed a mule deer (Odocoileus hemionus) sitting under a pear tree outside my kitchen window (near Lookout CA/Modoc County). Most mule deer in our area are infested with ticks. Several magpies were getting onto the deer’s back and picking off the ticks. Only one magpie at a time sat on the deer eating ticks while the others waited their turn. The deer was completely relaxed and comfortable with the magpies hopping all over its body, including on its face and between its ears. I watched for about 20 minutes before becoming otherwise occupied, but the magpies continued to feast for another half hour while the deer never stood up or moved away.
Unfortunately the photographs are not very good because it was evening, the pear tree was in partial shade and I did not want to disturb the mule deer and black-billed magpie so took the pictures through a double pane window rather than step outside.
There always is something interesting to observe in our yard, even when in the house doing supper dishes.