The Solitary Rook in Winter
A rook encountered alone in winter time is almost certainly the servant of a witch. The witch lives within the distance of one hex at a suitable location, and is now aware of the presence of the PCs unless one of them is carrying a branch from a Rowan tree. She will seek to: 1 - Enchant them to act as slaves; 2 - Enchant them to perform a task; 3 - Sacrifice them to the devil.
A Storytelling of Rooks
Rooks gather in the evenings in their dozens, hundreds or thousands - often close to a church or other holy site - to converse about the happenings of the day. Standing amidst them, surrounded by their cries in the gloaming light of the dying evening, a cleric or child can discern something of their discourse. Select a lair, adventure locale, or rumour the PCs have not yet discovered. This is what the listener hears about.
A Mother Rook with Young
A mother rook with her brood is a portent of disaster - and rebirth. The next time the first PC to spot the birds (determine at random) has to roll a saving throw, he or she fails automatically. If the result is death, a tree grows where the PC is buried within one month. It bears three apples, each of which restores all lost hit points if eaten.
Rooks Flying in the Wind
Rooks flying on a windy day, celebrating the skill and strength and speed in their wings, summon storms which reinvigorate the weary. Within d6x10 minutes the storm begins. It lasts for d3 hours; during this time travel is impossible without fatigue and sickness. After the storm has ended, the clouds dissipate and the PCs lose existing levels of fatigue; spell-casters recover spent spells.