Yesterday evening, I had an almost full hummingbird feeder;

[Backseat Driver]

about 6/8 full after several days of very hot weather in the 90s, that derecho storm that went through fast and did not do much damage in my area, and a few pop-up rain showers; it holds about 4 cups - this morning I look and see a feeder that is only perhaps 3/8 full - I only see perhaps 1 - 2 hummers sipping perhaps twice daily--a couple sips and off they go; where did all the juice go overnight? I investigated and noted no obvious leaks-- it's a glass feeder hung upside down on a shepard's hook with a bottom-filling plastic six flower screw-on plastic lid for filling with a stand so hummers can alight. Evaporation from those 6 tiny sipper holes in breezy conditions? Expansion/contraction of filling lid?Changes in barometric pressure push it out of those little holes overnight though dew point is higher yet without outside dried up evidence? Before I wash and change out the DIY nectar today, I have to say I'm stumped as to where all that nectar went in a single night.

[FalloutShelter]

1. I don't know where you live...

but I had a similar situation a couple of years ago and finally found out what happened when I installed a critter cam on my back deck. Turns out that bats were sucking down the nectar every night.

Not necessarily your problem, but it may be.

[Backseat Driver]

3. Interesting - our off-the-main-busy road, suburban townhouse faces a community retention pond

in which ducks, geese, turtles, and fish flourish. It's been visited by buzzards, hawks, owls, vultures, blue herons, cranes, and cormorants; we were surprised last week by a single swan visiting for about 3 days; sad, it seemed lonely. The darn Canadian geese weren't intimidated by its presence a bit! We've noted a few insect-eating bats in past years swooping around the pond hunting bugs when we walk the doggies at dusk, but none this year yet.

[liberalmuse]

2. I would bring it in at night.

Bring the feeder in when you're sure the hummingbirds have finished for the day (usually after dark) and make sure to put it back out early in the morning because the hummingbirds will need it right away when they wake up. The nocturnal critters stealing the nectar will eventually move on.

[AllaN01Bear]

4. bats?

some bats and moths are known pollinators as well.

[Silver Gaia]

5. Was it very windy at night?

If the feeder swings in the wind even the slightest, the nectar will spill out. This happened to my feeders a couple of times earlier this spring. I couldn't figure it out either until I noticed the sticky ground beneath them.

[Backseat Driver]

6. Not particularly, but I'll check that when I take it down to refill. Thanks for that tip.

[GentryDixon]

7. This is the first year I have had finches drinking from my feeder. 🤔

They horde the space, to the detriment of the hummers. They don't come around much since the finch have found the nectar.

Mine is a glass, upside down feeder as well.