Thursday, 4 December 2014

If Humans migrated.

Being off work with a shoulder injury for a few weeks now, has allowed me to spend time pondering a question that has floated around inside my head for a little while.
A question. A curiosity. I'm not sure which best defines it, nor the best way to word it?..

"How far could migratory animals migrate, if they were the size of Humans?"

"How far could Humans migrate, under the same abilities as those animals which migrate?"

"Pound for pound, which animals' migration is most impressive?"

I'm still not sure which of those sums it up best but, I'm sure you get the idea of what it is, that I've been contemplating.
Please bear with me, there are a lot of numbers and calculations below. I'm no biology or maths professor but at the same time, I've been as thorough as possible, without dedicating the rest of my life to studying every variable to what is not exactly, the easiest question to answer.
Working out a simple weight equivalant is not hard to do, get an average Human weight and divide by the weight of say, a Reed Warbler, will lead you to how far that Warbler would migrate if it were the weight of a Human. Or would it?.. I looked at few options to compare, to see what appeared to be the most accurate and going by weight actually seemed to be the most inaccurate.
For example, that would make a Barn Swallow (Hirundo rustica) weighing that of an average Human, capable of migrating 9.3 million miles. As impressive as migration is, that figure is just not accurate. The variables I referred to earlier are complex studies that to be quite honest, are beyond me but I feel it only fair to mention which factors I have purposely steered clear of.

Things that would be have to be considered to improve accuracy would have to include factors like different species' metabolism, aerodynamics at a greater size, even how the compostion of each body would affect results. ie: A Human body is made of 50-60% water, but what about say, a Cuckoo? How different would the compostion then be?
So far I'm doing a good job of explaining how NOT to be incredibly accurate but I wanted to show how much I have considered, when working out any kind of answer, and not wanting to sound like a vague school book that simply states "if you could jump as high as a grasshopper, you could jump over the Eiffel Tower" or similar inaccuracies like how a snake is 'poisonous'.
It's not.
It's VENOMous! (Sorry, a real bugbear of mine!)

I researched the length, weight and migration distance and then worked out the BMI of a select few species, which I think gives a slightly more accurate result, as opposed to height or weight alone.
I did this for five different species, those being;

Arctic Tern (Sterna paradisaea)
Avg weight - 100g
Avg length - 34cm
Avg BMI - 0.8650
Migration distance - Pole to pole, apprx 12,500 miles (one-way).

Arctic Tern - photo courtesy of Stewart Sexton
Arctic Tern - photo courtesy of Stewart Sexton
Arctic Tern - photo courtesy of Stewart Sexton

Barn Swallow (Hirundo rustica) 
Avg weight - 40g
Avg length - 16cm
Avg BMI - 1.5625
Migration distance - Various locations in Africa/S.Africa, I used a point at about mid-way of thier range: Gaborone, Botswana. Apprx 6,000 miles (one-way).

Taking a well deserved rest after a perilous journey from Africa

European Eel (Anguilla anguilla)
Avg weight - 1kg
Avg length - 55cm
Avg BMI - 3.3057
Migration distance - Sargasso Sea, near the Bahamas, apprx 5,100 miles (one-way).

European Eel (AKA Silver Eel) are said to not eat at all when on migration! 
(Photo courtesy of

Silver Y moth (Autographa gamma)
Avg weight - 100mg
Avg length - 24mm
Avg BMI - 0.1736
Migration distance - Origins vary from just over the Channel in France, Portugal etc, to possibly even sub-Saharan Africa. Again I made a mid-way estimate point, which was Tunisia, apprx 1,400 miles (one-way).

Silver Y - known for thier high altitude migration, often hundreds of meters up to make use of fast airstreams for assistance

Diamond-back Moth (Plutella xylostella)
Avg weight - 4mg (Pupal weight, but closest I could find and not too dissimilar)
Avg length - 8mm
Avg BMI - 0.0625
Migration distance - Migratory range thought to be very similar to that of the Silver Y, apprx 1,400 miles.

Diamond-back. Some do reside in the UK, those which are migratory share a similar range to the Silver Y.

Human (Homo sapiens)
Avg weight (globally) - 62kg
Avg height (globally) - 167cm (m+f combined avg)
Avg BMI (globally) - 22.2309
Migration distance - Nil. 0 miles.

Human...and a fine specimen at that. OK, maybe not.

Now, down to the business end of all this - my 'findings'. As I mentioned above, I'm still undecided on the best way to word THAT question, but my answer to it, will be stated below, as 'Human Equivalent' for ease.


To help scale some of the distances mentioned below, bear in mind that:
  • The circumference of the Equator = c25,000 miles.
  • Distance to the moon from Earth = c239,000 miles.


Calculating the human equivalent to these migrant species, by comparing the above BMI, results in this:

  • European Eels' journey = 5,100 miles.
  • Human Equivalent        = 34,298 miles!

  • Barn Swallows' journey = 6,000 miles.
  • Human Equivalent        = 85,367 miles!

  • Silver Y moths' journey = 1,400 miles.
  • Human Equivalent        = 179,281 miles!

  • Arctic Terns' journey = 12,500 miles.
  • Human Equivalent    = 321,256 miles!

  • Diamond-back moths' journey = 1,400 miles.
  • Human Equivalent                = 497,972 miles!

What does this all mean? 

These figures are accurate in giving an approximate answer. That sounds a contradiction in itself, however, what it has proven, is that this is exactly why there isn't an exact, definitive answer anywhere, to "THAT" question. 
Maybe someone is spending their lifetime on it now? Maybe not?

Either way I hope, that at the very least, this reaffirms what an incredible feat these animals undertake and what a wonder migration actually is.