Yer goin' there. Really, man? Who th' hell's askin' these questions? Jackass!
First the unasked question: yes I did watch Monty Python and the Holy Grail.
Second, I ain't a physicist.
Third, I don't give enough of a shit t' actually calculate it even if I were. Lucky for you that we have the internet. Style.org already kinda answered this one, which is good 'cause otherwise you wouldn't get squat.
There are all kinds o' swallows in Africa. 47 of the 74 species found worldwide as a matter o' fact. Whoever th' hell wrote th' article actually narrowed it down t' which one Arthur's talkin' about: th' South African Swallow.
Th' next factor is weight, but nobody gives a shit about African swallows so there's no data out there about it. Least not according t' the website I looked at. an' I don't care enough t' poke around any more'n a link or two in. So fuck African swallows.
Apparently some really bored scientists over in Europe measured swallows for 54 freakin' years an' came up with average weights an' wingspans, though. Who th' hell pays these guys? Some asshole on th' other side o' th' pond weighs birds as a goddamn CAREER an' prolly makes more money than I've ever had. Then again th' jerk prolly spent a hundred thou on education an' loan repayments jus' t' reach th' pinnacle of his damn life out in the wilderness somewhere with a fucking net.
Anyway, you need those things t' find velocity. An average European Swallow flies at about 24 miles an hour. Damn metric scale. Since they're European scientists they listed it in meters. Th' site's prolly American since they put it in mph too.
An' nobody cares about African swallows 'cept you, bud. Go spend your hundred thou an' th' rest o' your life measurin' 'em and maybe you'll get your answer.