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Can a swan break your arm?

BY Dan Keel

28th Jun 2022 Animals & Pets

Can a swan break your arm?
Could a swan break your arm, or is it just a misconception? Dan Keel explores this debate in this extract from his new book
Myriad works of literature exist stating that swans can break a human’s arm. No real-life examples can be found. Equally, there is a huge array of printed and online material suggesting a swan, with its hollow bones, simply lacks the brute force required to break a human’s thick bones. Again, there is no evidence. But I was still determined to take a stab at coming up with an answer.  

The makeup of a swan's wing

Let’s start by examining the makeup of a swan’s wing, as this seems the only remotely feasible weapon in its arsenal capable of breaking the limb of a fully grown man (its bill is capable of a nasty peck, but would struggle to even leave a bruise). A swan’s wing has around 10,000 feathers, is around 61cm (24in) long and weighs around 700g (1lb 7oz). As previously mentioned, the bones are hollow to save vital weight in flight.  
A swan spreading its wings
A swan's wing has around 10,000 feathers, is around 61cm long and weighs around 700g
The flight of most waterfowl sees them flapping their wings quicker than most birds. Unlike an eagle, the bodies of waterfowl are heavy and the wings relatively small in comparison. This means there is a relatively high load on the wing and that a large amount of flapping is required for a swan to remain airborne. The swan does however have a smaller wing-load compared to other waterfowl, meaning it only beats its wings 160 times a minute compared to your average duck, which flaps at 300 times. Why is this relevant? Well, it suggests the swan generates a decent amount of power from its large, broad wings and strong chest muscles. We already know a swan’s wing is capable of submerging a large struggling dog under water for more than a minute. We also know a swan’s wing can keep airborne a body mass of 12.2kg (26.8lb) for very long periods when migrating. But strong enough to break your arm? 

So, what damage can a swan do?

A force of 4,000 newtons is required to break a human femur bone (the one extending from your hip to your knee). An estimated force of 3,300 newtons is required to break the average rib. So let’s be generous and suggest that a force of 2,000 newtons is required to break the long thin radius bone extending from the elbow to the thumb. It is after all far less protected by fat and muscle compared to the femur.  
Can a swan generate that kind of force? To answer this question, I carried out a string of calculations using the formula Force = Mass x Acceleration. My work was based on the speed and acceleration of a swan’s wing, the weight of the wing and the length of the wing. The end result was that an adult swan’s wing can generate a force of 79 newtons, far short of the 2,000 newtons required to break an arm. Now, as you can probably tell, I am no scientist. I have used a number of assumptions. 
"Can a swan generate that kind of force?"
These are: 
  • That a swan’s wing weighs 0.7kg 
  • That the swan’s wing beat is one metre tall 
  • That the human arm in question is of average strength for an adult (i.e. not that of a child or an old person with a lower bone density
  • That a swan would attack a human with the same wing speed and acceleration it generates when flying 
  • That every single part of a swan’s wing moves at the same speed
Let’s say I am wrong on all these assumptions; would it make a big enough difference? Even if a swan’s wing weighs more, beats down faster when attacking and even if the swan chose to attack someone with particularly weak bones, there is simply no way these variables would bridge the gap between 79 newtons and the 2,000 required to break an arm. 

A real life case study

Those desperate to disprove this theory may stumble across the case of a 70-year-old woman who broke her wrist after being attacked by a swan in Dublin. The Irish Times reported in May 2001 how the pensioner failed in a £30,000 personal injuries action against the state after being attacked by an angry cob in Phoenix Park. Mary Ryan, from Castleknock, told Dublin Circuit Civil Court: “He knocked me to the ground. He continued to aggressively beat my legs and tried to peck me in the head.” 
"It was never made clear exactly how Ms Ryan’s wrist was broken in this unfortunate incident"
The article says a motorist pumping a car horn seemed to frighten the swan, giving the victim long enough to reach her vehicle. But Ms Ryan explained: “The swan followed me and started pecking at the car and beating at it with his wings.” 
Ms Ryan’s case centred on the claim that there were “no signs warning people as to the mischievous propensity and uncertain temperament of swans”. But the judge decided that neither park nor the state should assume ownership or responsibility for the actions of a swan which had merely flown in. Judge Kevin Haugh added: “The swan, like Oliver Twist, had come back looking for more and beat her to the ground.” 
Angry swan
Swans have a bit of a scary reputation
It was never made clear exactly how Ms Ryan’s wrist was broken in this unfortunate incident. But the judge’s concluding words suggest she was knocked to the ground. I am going to stick my neck out and suggest it was almost certainly the fall which caused her injury and not the swan’s wing. 
Can a swan break your arm? No. In fact, I would suggest a swan is more likely to break its own wing when attacking a human. 
Swan: Portrait of a Majestic Bird, from Mythical Meanings to the Modern Day by Dan Keel
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