No idea; I just thought it might be appropriate for a druid to check the information about natural lore that is given by somebody else.
Beyond the general info that Phar know, I would say Caerth would know more about how harpies (and rooks) live and behave in the region. For example, while harpies tend to live in temperate marshes, there aren't any major marshland territories in the Standlands. Harpies are more often encountered inland near the Iron Woods. Rooks on the other hand, can live almost anywhere in temperate and warm lands, even underground.
Most people who live on the coastline of the Strandlands have known someone who has been attacked by harpies (or rooks). The general populace doesn't know the difference between the two creatures. Most encounters happen near shore or in the fields of farmers, although harpies have been known to attack fishing boats.
Also, while harpies prefer fresh meat, rooks eat mainly carrion, but they will attack livestock.
Caerth has seen both of these creatures and would know the difference by sight alone. He's likely fought harpies before. Rooks are more elusive. The two creatures rarely co-exist. More often they attack each other, brutally. It takes an outside power to force them to fight together. Caerth knows that rooks are rumored to worship a foul, demonic being, but he doesn't know its name.
A rook's cawing sound extends to at least 200 to 300 ft. Caerth has seen grown men shake with fear after hearing the frightful noise rook's make.