Running the engine hot
Why Does a Hummingbird Eat All Day?
Hovering costs more than any other way of moving. The bill for it comes in every twenty minutes.
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Step 1 of 5
Hovering is the most expensive way to move.
A bird gliding gets held up by the air moving past its wings for free. A hovering bird must make all of that lift itself, from a standstill, without stopping.
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Step 2 of 5
So the engine runs extraordinarily fast.
The wings beat about fifty times a second and the heart runs past a thousand beats a minute. Nothing that size can idle at those numbers.
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Step 3 of 5
Which means eating almost constantly.
It visits a flower every ten to fifteen minutes through the day, and takes in something close to its own weight in nectar before dark.
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Step 4 of 5
Night is the real problem.
It cannot feed in the dark, and at that burn rate it would run out long before dawn. Simply sleeping is not survivable.
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Step 5 of 5
So at dusk it turns nearly everything off.
It drops into torpor — heart rate falls to a fraction, body temperature falls close to the air's, and it hangs there stiff and cold until morning warms it up again.
A hummingbird in torpor takes twenty minutes or so to come round. People finding one have often assumed it was dead.
The short version
A hummingbird feeds all day because hovering burns fuel faster than any other movement — and it survives each night by shutting nearly all of it down.
Try it yourself
Hold your arms straight out and keep them still. Holding a position with nothing to lean on tires you far faster than swinging them does.