Comment by smackay

It's a little abstract, but the map showing swallows breaking out of the south of Iberia, then rapidly heading north is rather cool. You'll get a much better feeling for what this shows, if, early next spring, you find a natural barrier like a river or estuary. Then you can see birds pushing north and understand what these maps are really showing. For extra drama, hope for a strong headwind, and your admiration of what 20 grams of determination can do, will only increase.