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Comment by burfog | Hacker News Reader

I wonder how much it really saves.

Unless there is some sort of bone oddity in the joint, the wings are not locked in place. The bird must still self-support via muscles.

Try it. The relatively bird-like way is like a gymnast on a pair of rings, arms horizontal. Doing things upside-down, consider standing with outreached arms holding heavy objects. It'd be half your body weight at the arm midpoints, which due to leverage is roughly like a quarter of body weight in each hand.

Even without any flapping, that is going to consume lots of energy.

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This 'relative bird-like way' makes no sense at all. Humans are not birds. They are not even related. They are completely different organisms.

Humans have had zero evolutionary pressure for minimizing energy expenditure while in hovering flight.

Birds had more than 150 million years to optimize their benefits for survival and reproduction [1,2]. They even survived the Cretaceous–Paleogene extinction event [3] where the evolutionary pressure of food scarcity was at an extreme.

[1] https://en.wikipedia.org/wiki/Evolution_of_birds [2] https://evolution.berkeley.edu/evolibrary/article/evograms_0... [3] https://en.wikipedia.org/wiki/Cretaceous%E2%80%93Paleogene_e...

The elbow and 'finger' joints are fully extended, so are locked and don't require energy to support. The pectoral muscles are supporting the weight of the bird, but they are very much stronger proportionally than ours.

But it's an interesting question. According to a couple of papers I found online [1][2], when soaring birds are soaring their energy use is not much higher than when sitting. Soaring is very efficient.

1. How Cheap Is Soaring Flight in Raptors? A Preliminary Investigation in Freely-Flying Vultures https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3893159/

2. Heart rate and estimated energy expenditure of flapping and gliding in black-browed albatrosses https://pubmed.ncbi.nlm.nih.gov/23661772/

Albatrosses apparently have some kind of a locking mechanism just for that. I would expect it in other soaring birds too.

https://en.wikipedia.org/wiki/Bird_flight#Basic_mechanics_of...

That's not a fair comparison at all.

The gymnast example is fighting against gravity with absolutely no external factor other than personal strength, but the warm air / wind resistance pushing against the wings that allows the condor to fly for so long without flapping is contributing immensely to their ability to hold the wings in place.

It would be more like having your arms and legs (by body weight) hanging in sheets (so the entire length), rather than rings at the end of them.

A few of the other comments have covered good reasons why this is a poor analogy. One thing to remember: wing muscles are the most well-developed muscles on birds, while human arms are extremely weak compared to our legs.

A better analogy would be that flapping-wing flight is to soaring how running is to standing (maybe on a moving platform to account for turbulence, etc.).

The birds are better built for it though. The keel in soaring birds is massive and not comparable to our weak chests.

It's not even that annoying for them apparently - birds can sleep (kind of) while soaring as well.

don't forget that the wings create lift, i.e., the body hangs between the wings, it's not the body that holds up the wings, it's the other way around.

Exactly, it's more like suspending yourself from your armpits

No, because of leverage. The air lifts all along the whole wing. On average, the air lifts from the middle.

So it's more like suspending yourself from your elbows, with your arms out horizontal.

I have no idea about birds, but I read that horses and other animals can sort-of lock their feet in place and require minimal effort to stay in place -- perhaps birds have such mechanisms as well and it takes very little effort to just glide -- otherwise, they would not do it.

The physics are different. For a gymnast the support is at the hands, so the force felt by the gymnast is a product of his weight and the distance between his shoulders and hand palms. For a bird I'm guessing that air applies support to the body and wings, so forces are more evenly distributed throughout its length.

This is a terrible comparison, bird physiology is nothing like human.

The energy saving is vast, the energy comes from external lift rather than burnt calories.

It’s like the difference between standing and running.

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