Yesterday I found a large flock of 75-100 Pinyon Jays in a sprawling subdivision to the little town of Salida, CO. Included in the flock were birds in juvenal plumage. I watched several of them foraging for pinyon pine seeds on the ground. Every bird I watched took the pine nut to a flattish rock then they jabbed the nuts with their bills to crack them open by using their toes to hold them in position. Apparently they have learned that it is difficult to crack open the nuts on the softer surface of the ground so they use the nearby rocks. As the ground under the pinyon trees was quite rocky, they didn't have to go far to find a rock and this saved the time it would take to go to one of the trees to wedge the nuts in the bark for stability when opening them. Very bright birds.
I also observed these jays cocking their heads like Robins do when they appear to be listening for worms in the ground. This would be followed by a jab into the ground where they apparently were killing invertebrates for food, a behavior described in Birds of North America online. SeEtta
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