What is the air speed velocity of an unladen swallow?

It depends on whether you are talking about an African or European swallow.

The airspeed velocity of an unladen swallow is roughly 11 meters per second, or 24 miles per hour*, beating its wings 7-9 times per second (rather than 43). But please note that a 5 ounce bird cannot carry a one pound coconut.

*Based upon published species-wide averages of wing length and body mass, initial Strouhal estimates based on those averages and cross-species comparisons, the Lund wind tunnel study of birds flying at a range of speeds, and revised Strouhal numbers based on that study gives an estimate that the average cruising airspeed velocity of an unladen European Swallow is roughly 11 meters per second, or 24 miles per hour.