How can a hummingbird exist?

DISCLAIMER: This is a maths heavy post. Sorry not sorry. 

Hummingbirds are freaks of nature. They exist at a speed and intensity that is incomparable to any aspect of human life. The more I read to write this piece, the more unconvinced I become that these organisms can feasibly exist. How does this family of birds live at this extreme a tempo? So many aspects of their life contain such ridiculous numbers; it is difficult to know where to begin.  

So let’s try to start with their wings. 

Their flight style of hovering is far more akin to that of insects than birds, but obviously hummingbirds retain a similar morphology to their avian siblings. Hummingbirds flap their wings through similar arcs to other birds (around 120ᵒ) but the simple “up down” motion that most other birds employ to achieve lift is not sufficient. The hummingbird needs to hover.  

So, how does a bird fly like an insect?  

The answer comes in two parts: with special muscle fibres and special wing strokes, and I will  try to explain these adaptations in a way that doesn’t include disgusting words such as ‘kinematics’ or ‘Matt Handley’. 

Let us begin. 

Simply put, birds make use of two major muscles to flap their wings: the pectoralis major and the supracoracoideus. To push their wings down (downstroke) and generate lift, the bird contracts the pectoralis major. To push their wings up (upstroke) and start the flap again, the bird contracts the supracoracoideus.  When a seagull flaps its wings, 100% of the lift that pushes the bird upwards happens on the downstroke.  

In hummingbirds, 75% of the lift is generated on the downstroke and 25% on the upstroke. The idea of something generating lift on the upstroke seems counterintuitive, but hummingbirds pivot their wings forward on the upstroke to force air under it, and their overall wingbeat takes the shape of a ‘figure-8’  instead of a flap. 

FlightPatterns_Hummingbird

Even so, hovering still requires a serious amount of wingbeats.  

A SERIOUS amount of wingbeats.  

The Amethyst wood star hummingbird completes a full wingbeat cycle 70 times a second.  

I’m going to force you to scroll for a second to fully take that information in. 

 

70 TIMES A SECOND

 

You know me*, I love context.  

70 times a second means one wingbeat every 0.0143 seconds. What can humans do in that time? 

Nothing.  

Or rather, certainly nothing consciously. An automated nervous response travelling from the top to the bottom of your spine would take about 0.0083 seconds to pass down a nerve cell. So, by the time your nervous system has realised that you’re touching a hot pan, the hummingbird is already on its upstroke. To put it into words that are more relatable, a hummingbird could flap its wings 21 times before you could blink.  

However, in the tapestry that is a hummingbird, the wings are merely a few weft yarns. What good are the muscles that power this incredible feat of flight without blood to supply them with oxygen and the essentials therein? An exceptionally strong heart is required. 

Relative to its size, hummingbirds have the greatest heart to body ratio of anything in the animal kingdom, coming in at 2.5% of its body size. That may not seem too excessive, but the heart that powers the blue whale, the largest creature to have ever existed, is only 0.43% of its body size. If a humans’ heart was 2.5% of its body size, it would weigh 1.74kg, which is nearly 7 times more than the average heart weighs. So we’re talking about something pretty good at pumping blood.  

Well it needs to be. A hummingbird heart rate can reach up to 21 beats per second, or once every 0.048 seconds. But again, this sort of statement is rather meaningless to us. Aside from computing and motors, there isn’t much we encounter daily that does anything at the rate of 21 times a second**. So let’s scale things up a bit. 

I found a small and most likely completely insignificant study into the effects of caffeine on human online. In it, four test subjects’ heart rates were measured in 15 minute increments after consuming 200mg of caffeine. On average, their heart rates rose from a resting rate of 68.5bpm to 81.9bpm.  

200 milligrams of coffee caused heart rate to increase by 20%. 

Therefore (and I realise that this makes neither mathematical nor biological sense) it is safe*** to assume that you would need 18390mg of caffeine to push a human heart rate up to that of a hummingbirds’. This is equivalent to drinking 194 cups of coffee simultaneously.  

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Let us venture back into a world of mathematics based on factual quantifiable things. Things such as the amount of energy needed to raise 1g of water by 1 degrees Celsius, also known as a calorie. Even on your heaviest days of eating, you will struggle to crack 3500 calories. Olympic biathletes, the one where you cross country ski and then shoot things, need to consume 6000 calories a day.  

Some hummingbirds, on their most ravenous of days, can consume an incredible 7.6 calories. 

Ok yes it doesn’t look too impressive when you see it at their level. So, let’s look at this when scaled up to our level. 7.6 calories for a hummingbird scales up to a human consuming 155,000. 

It’s that time again where I take a large number and apply some mental gymnastics. 

155,000 calories is: 

  • 100kg of hard-boiled egg. This is equivalent to 2500 eggs and it would take the average hen 2706 days to lay that many assuming it didn’t stop at any point. 
  • 742 bags of spinach. If you grew the recommended amount of spinach in a 10×10 foot allotment, it would take a total amount of 18 weeks to grow the necessary amount.
  • 18.5ml of petrol (that’s a lot, trust me). This is enough to take a new Toyota Yaris Hybrid 478 metres. Side note, there are 8.8 million calories in a litre of petrol, which makes our harness of it as a fuel source look woefully inefficient. 
  • 3229 McNuggets, or one night out in Cardiff. 
  • 0.097% of the energy in a lightning bolt. 

We’ve got off track again, but if you aren’t impressed that an animal lives off the human equivalent of 0.1% of a lightning bolt every day, I don’t know what to tell you. 

So that is the life of a hummingbird. And all that happens every single day.

And I didn’t mention they can fly backwards. They can also do that. 

 

* And I know that statement is true because only I will ever read this.

** Except Plymouth Argyle giving away penalties.

*** This is the worst piece of maths I will ever do, and I’m sorry for making you read it.

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