Eli5: Why does the nectar level change throughout the day in a hummingbird feeder?


At 7:30AM, there’s about 2inches of nectar in the feeder. By 1:30PM, the nectar is so low, it looks like there is none in the feeder. By 7:30PM, the nectar level is back up to about half an inch. It gets up to 105°F outside everyday.

In: 1

The air above the liquid is changing in temperature. It expands when it’s hot, and contracts when it’s cooler. If it’s in the sun, the feeder itself is likely getting much hotter than 105F. The liquid that was there in the morning got drank, evaporated, or got pushed out enough to overflow and drip out onto the ground. Then whatever was still in the plastic outside the lowest point of the central section part got sucked back into the glass when the air inside cooled off.

Changes in outside barometric pressure can also influence this, but unless you have a really huge hummingbird feeder, not enough to explain all of it.