[wongarsu]

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

[lukan]

Or you could have talked to people who travel.

[dlenski]

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.