The guide on the "Crocodile Tour" near Carara National Park in Costa Rica told us the swallows follow the boat because our breathing containts CO2, which attracts insects. I suspect the boat exhaust has 100 times more CO2, but wonder if even that would cause the effect he described.
And in cause you were wondering, it is not easy to take photos from a tourist boat. The wetlands in this area are a birdwatcher paradise, but I left with just few photos.
This species can be identified by the white stripe on the face.
Africa (entire continent rather than south of Sahara)
AN
Antarctica
AO
Atlantic Ocean
AU
Australasia (Wallacea (Indonesian islands east of Wallace's line), New Guinea and its islands, Australia, New Zealand and its subantarctic islands, the Solomons, New Caledonia, and Vanuatu)
PAL
Eurasia (Europe, Asia from the Middle East through central Asia north of the Himalayas, Siberia and northern China to Japan)
IO
Indian Ocean
LA
Latin America (Middle and South America)
MA
Middle America (Mexico through Panama)
NA
North America (includes the Caribbean)
NO
Northern oceans
OR
Oriental Region (South Asia from Pakistan to Taiwan, plus Southeast Asia, the Philippines, and Greater Sundas)