Strange Raven buries a rock

At Mammoth Hot Springs in Yellowstone National Park, we witnessed the inscrutable behavior of a very strange raven.

When we spotted him, he was carrying a white rock in his beak and walking over the dusty ground between terrace formations.

After choosing a site, he put the rock down and began to dig a hole in the ground with his beak.

However, after placing the rock in the hole, he was not satisfied, and dug up the rock to carry it to another part of the ground.

This happened three or so times while we were watching, until he finally seemed content with the burial site of his rock. The job done, he took to cawing.

After a moment, a magpie alighted and began to yell at him.

I've never seen a raven do anything like this before. Their Wikipedia entry seems to shed some light:

Common Ravens have been observed to manipulate others into doing work for them, such as by calling wolves and coyotes to the site of dead animals. The canines open the carcass, making it more accessible to the birds. They watch where other Common Ravens bury their food and remember the locations of each other's food caches, so they can steal from them. This type of theft occurs so regularly that Common Ravens will fly extra distances from a food source to find better hiding places for food. They have also been observed pretending to make a cache without actually depositing the food, presumably to confuse onlookers.

Common Ravens are known to steal and cache shiny objects such as pebbles, pieces of metal, and golf balls. One theory is that they hoard shiny objects to impress other ravens. Other research indicates that juveniles are deeply curious about all new things, and that Common Ravens retain an attraction to bright, round objects based on their similarity to bird eggs. Mature birds lose their intense interest in the unusual, and become highly neophobic.