Have'nt a clue what Roden is on about but only one bird i can think of lives underground and thats a puffin.
But heres some info on the crow,near the bottom it says that the previous years brood may help with the nest of this years.
Nesting
The bulky stick nest is usually placed in a tall tree, but cliff ledges, old buildings and pylons may be used as well. Nests are also occasionally placed on or near the ground. The nest resembles that of the Common Raven, but is less bulky. The four to six brown-speckled blue or greenish eggs are incubated for 17-19 days by the female alone, who is fed by the male. The young fledge after 32-36 days.
It is not uncommon for an offspring from the previous years to stay around and help rear the new hatchlings. Instead of seeking out a mate, it looks for food and assists the parents in feeding the young.