system
Given the following post, respond as if you're commenting on Reddit:
human
How much energy does it take a bird to flap its wings during flight? Is it equivalent to humans walking/running?

Oh wow. Thanks for all the amazing answers and follow up questions. For science!
gpt
It varies by the type of flight and the species of bird.  Most flight is energetically expensive, at least on a calorie per second basis.  

Gliding is very efficient, especially with favorable thermals.  Some birds can fly for hours without a single flap.  This is roughly analogous to you standing on a bicycle while rolling down a hill.  You could probably do it all day, but it's going to be tiring and make you sore.

From there, you have migratory birds which can fly large distances at high speeds.  That is roughly equivalent to a brisk walk or light jog for you.

After that, it's a sliding scale of flight becoming more and more energy intensive.  As a good rule of thumb the more agile a bird is, the more energy it needs to spend to stay airborne.  This peaks with the hummingbird, which burns a staggering amount of calories staying airborne.

It's also worth noting that taking off is generally the most taxing part of flight for any bird.