Speed Of An Unladen Swallow

To begin with, I needed basic kinematic information on African and European swallow species.

left: South African Swallow
right: European Consume

Although 47 of the 74 worldwide swallow species are found in Africa,¹ but two species are named after the continent: the West African Consume (Hirundo domicella) and the South African Swallow (Hirundo spilodera), also known equally the South African Cavern Swallow.

Since the range of the South African Eat extends only as far north every bit Zaire,^two I felt fairly confident that this was the non-migratory African species referred to in previous discussions of the comparative and cooperative weight-bearing capabilities of African and European swallows.^three

Kinematic information for both African species was difficult to find, just the Barn or European Swallow (Hirundo rustica) has been studied intensively, and kinematic data for that species was readily available.

It'south a simple question of weight ratios

A 54-year survey of 26,285 European Swallows captured and released by the Avian Demography Unit of the University of Capetown finds that the average adult European swallow has a fly length of 12.2 cm and a body mass of xx.3 grams.⁴

Because wing beat frequency and wing amplitude both calibration with trunk mass,⁵ and flight kinematic data is bachelor for at least 22 other bird species,^six it should be possible to estimate the frequency (f ) and aamplitude (A) of the European Consume by a comparison with similar species. With those two numbers, it volition be possible to estimate airspeed (U).

In order to maintain airspeed velocity, a eat needs to beat its wings forty-iii times every second, right?

Actually, incorrect. By comparing the European Eat with bird species of similar body mass, nosotros can estimate that the eat beats its wings 18 times a 2nd with an amplitude of 18 cm:

Species	Body mass	Frequency	Aamplitude
Zebra Finch	13 g	27 Hz	11 cm
European Swallow	xx g	≈ 18 Hz?	≈ 18 cm?
Featherlike Woodpecker	27 k	14 Hz	29 cm
Budgerigar	34 g	14 Hz	15 cm

Notation that even the tiny Zebra Finch flaps its wings no more than 27 times a second while cruising.

If we ignore trunk mass and look just at bird species with a like wingspan, we tin can estimate an average frequency of fourteen beats per 2d and an amplitude of 23 cm:

Species	Wingspan	Frequency	Amplitude
Budgerigar	27 cm	14 Hz	fifteen cm
European Swallow	≈ 28–thirty cm	≈ 14 Hz?	≈ 23 cm?
Downy Woodpecker	31 cm	14 Hz	29 cm
European Starling	35 cm	14 Hz	26 cm

By averaging all half dozen values, we can estimate that an average European Eat flies at cruising speed with a frequency of roughly 15 beats per second, and an aamplitude of roughly 22 cm.

Skip a chip, Brother

Last month's commodity on The Strouhal Number in Cruising Flight showed how simplified flight waveforms that graph aamplitude versus wavelength can exist useful for visualizing the Strouhal ratio (fA/U), a dimensionless parameter that tends to fall in the range of 0.2–0.4 during efficient cruising flying.

For a European Swallow flying with our estimated wingbeat aamplitude of 22 cm, the predicted blueprint of cruising flight ranges from a Strouhal number (St) of 0.2:

... to a less efficient 0.4:

If the first diagram (St = 0.2) is accurate, then the cruising speed of the European Swallow would be roughly 16 meters per 2d (15 beats per 2d * 1.ane meters per beat out). If the second diagram (St = 0.4) is accurate, so the cruising speed of the European Swallow would be closer to 8 meters per second (15 beats per second * 0.55 meters per trounce).

If nosotros settle on an intermediate Strouhal value of 0.3:

Nosotros can guess the airspeed of the European Swallow to be roughly eleven meters per second (15 beats per second * 0.73 meters per beat).

Three shall be the number chiliad shalt count

Airspeed tin also be predicted using a published formula. By inverting this midpoint Strouhal ratio of 0.3 (fA/U ≈ 0.three), Graham Chiliad. Taylor et al. show that every bit a rule of thumb, the speed of a flying animal is roughly three times frequency times aamplitude (U ≈ 3fA).⁵

We now need only plug in the numbers:

U ≈ threefA
f ≈ 15 (beats per second)
A ≈ 0.22 (meters per crush)
U ≈ 3*15*0.22 ≈ 9.nine

... to estimate that the airspeed velocity of an unladen European Swallow is 10 meters per second.

Oh, yeah, I hold with that

With some further written report, it became clear that these estimates are accurate, though perhaps coincidental.

An actual study of two European Swallows flying in a depression-turbulence wind tunnel in Lund, Sweden, shows that swallows flap their wings much slower than my estimate, at simply 7–9 beats per second:

"Compared with other species of similar size, the swallow has quite low wingbeat frequency and relatively long wings." ⁷

The maximum speed the birds could maintain was 13–14 meters per second, and although the Lund study does not talk over cruising flight in particular, the most efficient flapping (vii beats per second) occurred at an airspeed in the range of eight–xi meters per 2d, with an amplitude of 90–100° (17–19 cm).

And there was much rejoicing

Averaging the above numbers and plugging them in to the Strouhal equation for cruising flight (fA/U = 7 beats per 2nd * 0.18 meters per crush / 9.5 meters per second) yields a Strouhal number of roughly 0.13:

... indicating a surprisingly efficient flight design falling well below the expected range of 0.2–0.iv.

Although a definitive respond would of course require further measurements, published species-broad averages of wing length and trunk mass, initial Strouhal estimates based on those averages and cross-species comparisons, the Lund air current tunnel study of birds flying at a range of speeds, and revised Strouhal numbers based on that report all atomic number 82 me to estimate that the average cruising airspeed velocity of an unladen European Swallow is roughly eleven meters per second, or 24 miles an hr.

What is the majuscule of Assyria?

For those looking for additional answers, the four capitals of Assyria were Ashur (or Qalat Sherqat), Calah (or Nimrud), the short-lived Dur Sharrukin (or Khorsabad), and Nineveh.⁸ The ruins of all four aboriginal cities fall within the modern country of Iraq.

References

Thanks to everyone who has written in with comments and questions. Responses are posted here, forth with a revised guess from Dr Graham Taylor, and some alternating theories.

Chris & Tilde Stuart
Birds of Africa: From Seabirds to Seed-Eaters
MIT Press (1999)
G. L. Maclean
Roberts' Birds of Southern Africa
John Voelcker Bird Book Fund, Cape Town, S Africa (1985)
Graham Chapman, John Cleese, Eric Idle, Terry Gilliam, Terry Jones, Michael Palin
Monty Python and the Holy Grail
Python (Monty) Pictures Ltd. (1975)
Avian Demography Unit
SAFRING results of the European Eat (Hirundo rustica)
Department of Statistical Sciences, University of Greatcoat Town (2002)
Graham K. Taylor, Robert 50. Nudds, Adrian L. R. Thomas
Flying and swimming animals cruise at a Strouhal number tuned for high power efficiency
Nature 425, 707–711 (Oct 16, 2003)
Email correspondence with Graham Taylor of the University of Oxford Zoology Section (October 22–23, 2003)
Kirsty J. Park, Mikael Rosén, Anders Hedenström
Flight kinematics of the barn consume (Hirundo rustica) over a wide range of speeds in a wind tunnel
The Journal of Experimental Biological science 204, 2741–2750 (2001)
Ashur Red
Assyrian History
The Mesopotamian Encyclopedia (2001)