Bird migrations aren't that easy to observe with 1822 tech either. It's not like they could stick a GPS recorder on a bird, or mark a bird and follow it in a car. You can make local observations (many birds fly overhead, heading South-East) but with how difficult travel was it's not trivial to piece that together to the conclusion that birds travel from Europe all the way to Africa
During the early age of scientific inquiry in Europe, very few human travelers were following the white stork's migration route (Europe→Anatolia→Levant→Nile→East Africa), and I'd guess that most of those who did were from the Muslim world and not particularly accessible to European observers.
The small number of long-distance travelers and cultural contacts between the Eastern Mediterranean and Western Europe did result in lots of valuable learning; this particular bit of learning just took a while.
