The parent Orioles are trying to coax the chicks out of the nest, and the chicks are having none of it. The soft single note is the parent's calling the chicks to come to the food, the steady chittering is the chicks demanding room service. At one point, you can see the female shoot up into the clump of leaves that hides the nest, and it ends with the male flashing his beak full of caterpillars in an attempt to get the chicks to come to him. I watched them try this for an hour tonight, the chicks didn't budge.